design and alloy

VZerone

Active Member
#21
I've done a lot with COWW and 50/50 alloy...with no tin added and hadn't nary a problem casting fine bullets. I guess you fellows know I'm not in favor of adding more tin. I know the 50/50 is better for hunting because it doesn't fragment as much as straight COWW do. Air cooled COWW's do a half decent job though depending on caliber and velocity.
 

fiver

Well-Known Member
#22
lets work with the 165-A since the pictures seem to show the flow the best.
and is the one I was trying to explain to Bama in the side bar.

look how it went into the sizers and into the rifle with the ability to take very little damage.
the shape changed but the bullet was not really damaged.
now it didn't start to take the rifling just yet but you can see how it is getting closer to the diameter of the nose.
the area that will take the rifling is also the area that the nose will be trying to slump back into.
there is not all that much room left for any alloy movement there, everything is getting squeezed into a smaller area.
the nose is engraved into the rifling holding everything square to the barrel, so any other movemet is outward and even.
as it does move it engages more and more of the rifling which is taking up more room forcing any slump to fill the barrel fully.
the alloy allows this movement to happen in a controlled consistent manner from shot to shot, and doesn't really fight it happening.

we can do the xcb later and if anyone else wants to give the explanation of it or the silh. bullet a shot have at it.
 

Brad

Administrator
Staff member
#23
The 30 Sil and 165A are designed to let the alloy move. Rather than fight it, control it. As the rifling engraves and the nose bumps into the rifling it is held concentric.

The 30 Sil and 165A also have a large enough grease groove to help with metal movement on the rear end. As the rifling is engraved and pressure rises the alloy wants to flow. A grease groove can help give that metal a place to flow into rather than rivet.
 

Ian

Well-Known Member
#24
This is all well and good with tight throats and the 165A, but what happens if you have a sloppy chamber neck, oversized throat vs. groove, OR the big whammy, a self-loading rifle?

What if you cannot have the bullet touching anything steel when the cartridge is chambered because it might bind the weak camming action of an AR-10?

What do you do when you're loading cast bullets for an M1A/M14 and the brass has to be sized to minimum specs to function, and the chamber is loose, and there's a 200-lb ejector spring cramming the case to one side, and a mighty extractor claw pulling the rim hard against the ejector plunger, forcing the cartridge a full degree or two out of alignment with the bore axis?

That's where the original .30 silhouette by 45 2.1 comes in. It was designed for a bolt action rifle originally, but it turns out the design works well in a lot of things. It has no bore-riding, parallel nose section, so it isn't dependent upon precise static fit in the lands to work. It has two tapers to the nose, making a concave shape like a trumpet bell, just about the shape that most rifle throats tend to wear. If you load it so that it has a little jump to the throat, and don't use a powder that's too fast, and cast it from a ductile alloy, it will squirm around and self-align even if the case is crooked in the chamber. The deep, single lube groove and small "stem" transfer pressure on the base directly to the front section of the bullet, expanding out the nose as the metal from the front shoulder folds back into the lube groove area. As the lube groove is squeezed, lube is pumped out into the gap at the front of the case mouth, making a sort of lube bridge which helps the base funnel straight into the throat, even if the base was a touch crooked in the case neck.

In order for all this to occur and the bullet end up straight in the bore, the alloy must be flexible and be ductile, or able to "draw" easily. Tin inhibits draw, a good thing with some designs, not so good with others. There's a reason regular jacketed bullets don't have tin in their cores, and don't have displacement grooves: They elongate when the lands squish into the sides of the bullet, and the easily drawn core allows the bullet to stretch out easily. Same thing here, we want the bullet to wiggle itself straight, fold up into the throat, bump the nose into the grooves, and wiggle the base into the throat straight right before the pressure and speed of movement gets to great that it just turns to putty and deforms all over the place.

This is a matter of getting the alloy right and timing the pressure via powder selection so the bullet completes its metamorphosis without getting crooked in the bore. Basically, it's like a good baseball hit, timing and force are everything and if it's set up right, it works like it's supposed to every time. Yes, it takes some fiddling, and I did a whole lot of fiddling before I began to get and inkling of how to make this bullet work, but it does work very well, and will work in rifles where a bore-rider is out of the question, and a Loverin can't handle the velocity.

The way I see it there are two schools of fit, which sometimes overlap when you get into pressures which bump metal completely up through the nose to fill the grooves. School one is heavy on the static fit, meaning the 165A, which is perfect for a throat with some parallel freebore and an abrupt ball seat angle. When loaded, good static fit and alignment is achieved with a firm land engrave in the nose and light scuff on the front band from the freebore part of the throat. School two is heavy on the dynamic fit, meaning throw the bullet in there any old way you can, give it some room to find center, and blow it right up the middle with a perfectly-timed pressure front. The overlap involves the nose bump after the gas check is just entering the throat. With low to medium-pressure loads, this isn't a factor, but at high pressure/high velocity, the alloy will yield to some degree and metal displaced by the throat squeeze and lands will favor the nose since the pressure behind is greater than the alloy's plastic strength. F. W. Mann found out over a hundred years ago that bumping a bullet straight into the rifling was even more effective at achieving a balanced, concentric bullet than was a precisely fitted and breech-seated bullet. He tried and tried all sorts of ways to pre-position a bullet perfectly straight in the bore with a perfectly square base, and still found that it slumped crooked due to never being able to control the forces of starting from a standstill evenly. If the bullet is bumped AS it is moving, the metal tends to flow more evenly in the nose area and keep the nose point in the center of the bore.
 
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Ian

Well-Known Member
#25
The NOE XCB bullet I have yet to shoot, but I designed the first one and have some bench time with it. The whole concept is minimizing the amount of free space for lead to go sideways, and matching the throat angle precisely with the nose angle. When working out the XCB reamer design and the AM 31-190X bullet that was to match it, I used the term "Morse Taper Fit", which will be familiar to any machinist. Matching tapers will always align themselves perfectly straight when pressed together. The limiting factor is they have to be pressed together in the static state, for there is very high contact pressure at two small points of it is even slightly crooked, and soft lead deforms very easily. Parking the bullet in the throat for a perfect fit means it takes a lot of pressure to get it moving, which puts a lot of pressure on the bullet base. My bullet had one, deep lube groove and had a nasty tendency to rivet in the neck due to the extremely high engraving pressure. The NOE design has multiple, small lube grooves which makes a stronger core and combats the riveting tendency somewhat. There is also more room between the three grooves for metal to displace as the bullet engraves, and the flow forces are broken up before they get to the core and distort the whole bullet. This is sort of a hybrid between the silhouette-style bullet with throat-matching nose taper and the Loverin bullet with small lube grooves the whole length.

What seems to be working the best with the NOE version of the XCB bullet is a very tough, malleable alloy with a good deal of tin in it to make it resilient and resistant to lengthwise flow. The whole idea being to deform the bullet as little as possible as it engraves, so it cannot slump or bump at all, just start out straight and squeeze straight into the bore without the nose achieving the plastic state, while the displaced metal from the back part of the nose and the driving bands flows into the lube groove areas without disturbing the core material which could cause the bullet to bend or the nose bump up more on one side or the other. Slow powders are the name of the game here, for if the pressure spikes up too fast while the bullet is resisting the throat taper, the base will rivet anyway and it won't do it straight unless the whole neck is filled up with brass and lead....then you have other problems.

When I cast my XCB bullets from too soft of an alloy (air cooled 50-50) and punched them with 13.5 grains of Unique, they left neat little lead rings at the end of the case mouths and shot for diddly. When I used 4350, they shot ok to about 1800 fps and then petered out while beginning to leave lead rings and lead streaks in the bore. When I used straight wheelweights air cooled, they shot great with Unique and didn't leave lead rings, but I was stuck at 1500 fps. When I tried 4350 I got to about 2,000 fps before the lead rings showed up and accuracy again went south. I kept strengthening the alloy and hitting it with different powders but always came up against a point where the base would rivet and the accuracy would fall off. Understanding that riveting was the issue due to starting against a load, I tried seating the bullet deeper to give it some jump. That worked out ok, but still didn't get the groups I wanted at any speed, with any powder, or any alloy I tried. In retrospect, Taracorp Magnum, water-dropped, with about .015" jump to the throat, and no more than one thousandth total neck clearance and with a high-stearate, stiff lube, just might have worked, but instead I decided to take the lessons learned from the bullet and abandon it in favor of an easier tack....which due to the throat shape ended up being the MP .30 silhouette. Due to the tight tolerances of the XCB chamber, I had to size the bullets to .3105" and turn the necks for a close fit, sort of "pre-slumping" the bullet. I also found I had to nose-first size the bullets, then apply checks and base-first size them to crimp and lube or the metal didn't move correctly. At .3125" as-cast the bullets didn't like getting sized that much, nor were they designed to be until fired, but I made them work and with a little jump, a relatively soft, ductile, 50/50 COWW/SOWW alloy with no additional tin performed admirably. Here are some groups I shot back to back at a hundred yards, without perfecting the workup, at just under 2700 fps from a 23" barrel:

30 xcb 30sil HV groups.jpg


Here is a pound cast of the XCB chamber, together with a loaded cartridge and a dummy that had been chambered and removed to show the engraving. I put the pound cast back in for some reason, so that's why it has double engraves on it, but you can see how close the static fit of everything, including the loaded chamber neck, is. BUT.... even then, it was still super-easy to screw it all up and get shotgun-pattern groups if the alloy and powder weren't perfectly selected. I don't seem to have a photo of a loaded MP 30 Silhouette for this cartridge, probably because I shot them all, stuck a fork in it, and moved on to other things.

XCB pound cast.jpg

Here's the AM31-190X first as cast, then tapped into the throat unsized at .311", then sized .3105" for the .3108" throat entrance and tapped into the throat. Looks great, don't it? What could possibly go wrong? Well, as I explained, lots. You STILL must get the static fit, jump, run, and bumping dynamic fit just right via powder burn rate and alloy selection or it will find a way to go south on you in a big hurry. AM30190x.jpg
 

fiver

Well-Known Member
#26
I think I still have that one you sent me in the 0-6 case.

okay now we have seen why we use a different alloy with the different designs, and why the powders speed is important.
in one case starting fast and going slower is more optimal and in the other starting slower and working faster is going to show us what the alloy and what it has to endure is going to give us in each rifle.

the XCB design is similar to some other designs out there, the rcbs 0-55s is in basically the same position and responds the same to the alloy changes.

one of the things we haven't talked about is giving up alloy BHN in order to control the initial fitment.
a BHN made up from a perfect alloy structure is pretty meaningless if we are screwing the whole thing up by shooting the bullet.
a wide funnel shaped throat is going to do a whole lot better with a design that has a nose shape capable of squirting across and taking the edge of that funnel and bouncing it's way into the center without the bullet bending or being bashed up,
that of course means some hardness is required.
but diameter is not always your friend dropping down from a 5/5 type alloy to a 3/3 alloy and losing almost a thousandth in diameter in the process plus the ability to size another one can prove to be more beneficial than the few points of hardness you lose..
 
#27
The 165a is made for a 308 win saami throat. It was cut with a brand new ptg reamer fixed pilot. I had Ross Schuler cut thread and chamber a factory rem 700 barrel that had a crooked chamber. It cleaned up perfect to fit my savage. That shot very well. As run knows he ended up with the first mold.

He was the one that helped set the amount of bearing on the front drive band. We wanted to keep the gas check out of the body of the case. Even with that wide nose it feeds perfect in the savage stagger feed.
 

Will

Well-Known Member
#28
First I want to say I’m learning a lot here and really enjoy this thread.
What I have a hard time understanding is why a bullet like the AM 31-190X will not work. To me it looks almost perfect.
I did notice on the AM 31-188G unlike the AM 31-190X the bullet has a strong taper right at the ball seat area and a little less nose diameter.
Does the nose being smaller and the sharper taper in the ball seat area allow you to use a more ductile alloy that is able to self align? Are you getting any engraving on the 188G other than the foreword most portion of the ball seat area?
 

Brad

Administrator
Staff member
#29
Go back and read what Ian said about the 190X.
With the perfect fit the nose is held tight. Sounds great, in theory.
In actual use what you discover is that a certain amount of force must be applied to the bullet to engrave the rifling. With that much land contact the force required is much higher than in a bullet like the 165A with far smaller land engagement on seating.
Because the nose can't move until a certain force level is applied the bullet doesn't move initially on firing. Sounds good except for the reality of igniting all that powder behind it. If the pressure curve gets ahead of you the bullet base moves too much before the nose engraves and the bullet rivets. Think about it, that soft lead bullet fills in any space it can, like the space at the end of the neck of the chamber. The base is moving forward, the nose is held firm, and the lead has to go somewhere. This all happens very fast.
Like Ian said, with lower pressure loads and the right alloy it works great. Where is fails is where we exceed the strength of the alloy with the pressure curve.
That nose shape also really needs a berry straight feed into the throat. It doesn't self center if it jumps to the rifling from any real angle. If we have a .007 difference between loaded round and chamber neck dimensions the bullet is not fed straight into the throat. That "Morse taper fit" doesn't self align so well and all in for naught.
I really like how the 30 Sil self centers and handles the pressure. Before I got rid of my XCB rifle I was firing a 3% Sb, 1% Sn heat treated bullet at 2700 fps with RE15 into 1.5-2" groups at 100 with a varsity ofmcharge weights. Pressure was approaching 50K PSI and the bullet never failed. No leading, no blown up groups, no issues at all due to design failures. What I did learn was that it wanted a running start. It liked 15-25 thou jump.
 

Will

Well-Known Member
#30
I read it several times Brad it is just hard to understand how such a subtle change makes a such a huge difference. The more I learn about shooting cast bullets at higher velocities the less I know.
 

Brad

Administrator
Staff member
#31
There in lies the real key, that subtle changes do make a big difference.
Going from 4350 to 4831 may make all the difference in the world. Hell, going from A4350 to H4340 or I4350 may be the key.

It is all a matter of how the bullet design and alloy interact with the throats and chamber when kicked in the butt but expanding powder gasses. The launch of the bullet takes enough time for the bullet alloy to move. We can either try to control it via design, tight chamber, turned necks with no gap at end due to sloppy chamber, etc or we can use a bullet design, like the 165a, that determines HOW the lead can move.
If we design a bullet that takes the lead flow into account and therefore use it to an advantage we eliminate a huge source of trouble, don't we?

The 165A and 30 Sil are design that way- look at where the lead will flow and design a bullet to take that into account and make it happen in a repeatable, concentric manner.

Don't forget how alloy comes into play. Adding Sb does make a bullet harder but it doesn't inhibit the flow of lead under a swaging force. Adding tin doesn't add as much hardness but does rapidly change how easily the lead flows under thesame swaging force.

Lead bullet cores, lead pipe, and lead wire often have Sb added not only as a hardener but because it can make the swaging easier. These same products will almost never have tin as it would require far more force to get the same product.

Adding tin can be used to retard flow of the alloy a bit in some cases. Should we find our 164A is flowing too much under pressure a small increase in tin may slow the process and allow us to use a bit more pressure in the load.

In the end it is all about one word- BALANCE.

The right powder curve, charge weight, design, alloy, and throats all interact just right to make happy things happen. Alter anyone too much and it all falls apart.
 

Ian

Well-Known Member
#32
Will, please keep asking questions when something doesn't quite make sense, that's the whole point of the thread. This isn't rocket surgery, I just have a really hard time disseminating the concepts as I understand them down to a few sentences like Fiver can. Brad explained exactly what I was saying about the 190X in different words, maybe a little more clearly.

I wrote about the 190X to make a big point here: Just because you think you followed someone's instructions to the tee and have a perfect static fit situation...don't mean squat once the primer is struck. You MUST get the alloy and the powder pressure to work with the bullet shape or things will go to hell and some people will start to develop wild theories.

If you're shooting 1200 or 1500 fps, you can get away with an overly stiff alloy (like air cooled wheel weights) and a two-diameter bullet where the nose fits the bore and the drive bands fit the throat...like the 165A, or most Lee rifle bullets....but when you start getting above 30K psi and 1800 fps, that fit, alloy, and pressure concept goes out the window, and like Fiver wrote earlier, even your mid-range loads can be improved if you apply the same concepts that are necessary at high velocity.

How well does anyone think Waco's NOE XCB bullets match his .308"'s throat? I'll bet you other than entrance diameter, not worth a damn. BUT, it shoots.....so the question is why?
 
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fiver

Well-Known Member
#33
I know the answer to that one.
he hadn't measured his throat before he started but he did have a clue that it was not cut like the throat Tomme describes [which it seems is how many rifle makers are starting to cut them now]
so option B of the [picking a word for the balanced alloy is tough] bunch was the best choice for that situation.
it needed to make it across the gap and get funneled into place.
this is what Michael was facing when he designed the ranch dog molds too BTW, he relied on the nose to hang on out there in the open take the hit and get everything straightened out before moving along.

so.
what this throat shape thing does is helps us determine which bullet and alloy to use.
and why we should use them to work around the problems we face.

this is why even after I see you guy's having success with the different bullet designs I ask for a pound slug to be done.
the only way we can 'see' what is happening is by knowing the pressure rise, alloy, distance to the hole in the barrel, and the bullet and throat shape relationship.

one more short thought.
if the nose is bouncing about trying to center itself what is happening at the back end?
you know the part that was supposed to be holding everything in line to begin with.
 
#34
keep going down these lines..
I agree that bullet design and alloy are two of the major players in the game but this is also part of the problem, there is no real definitions to follow to say "this is a good design or best design or this is the alloy that is best in this design at x speed. Seem like everything is empirical at best.. I believe I have a reasonable handle on how the bullet goes down the barrel and effect of high rotational speeds from non centrifugal cast materials (still have scar where purchasing agent order standard non centrifugal cast 12 in 316 l tube which later turned to 14K rpm. After that we installed 2" thick blast shields.
The NOE XCB bullet I have yet to shoot, but I designed the first one and have some bench time with it. The whole concept is minimizing the amount of free space for lead to go sideways, and matching the throat angle precisely with the nose angle. When working out the XCB reamer design and the AM 31-190X bullet that was to match it, I used the term "Morse Taper Fit", which will be familiar to any machinist. Matching tapers will always align themselves perfectly straight when pressed together. The limiting factor is they have to be pressed together in the static state, for there is very high contact pressure at two small points of it is even slightly crooked, and soft lead deforms very easily. Parking the bullet in the throat for a perfect fit means it takes a lot of pressure to get it moving, which puts a lot of pressure on the bullet base. My bullet had one, deep lube groove and had a nasty tendency to rivet in the neck due to the extremely high engraving pressure. The NOE design has multiple, small lube grooves which makes a stronger core and combats the riveting tendency somewhat. There is also more room between the three grooves for metal to displace as the bullet engraves, and the flow forces are broken up before they get to the core and distort the whole bullet. This is sort of a hybrid between the silhouette-style bullet with throat-matching nose taper and the Loverin bullet with small lube grooves the whole length.

What seems to be working the best with the NOE version of the XCB bullet is a very tough, malleable alloy with a good deal of tin in it to make it resilient and resistant to lengthwise flow. The whole idea being to deform the bullet as little as possible as it engraves, so it cannot slump or bump at all, just start out straight and squeeze straight into the bore without the nose achieving the plastic state, while the displaced metal from the back part of the nose and the driving bands flows into the lube groove areas without disturbing the core material which could cause the bullet to bend or the nose bump up more on one side or the other. Slow powders are the name of the game here, for if the pressure spikes up too fast while the bullet is resisting the throat taper, the base will rivet anyway and it won't do it straight unless the whole neck is filled up with brass and lead....then you have other problems.

When I cast my XCB bullets from too soft of an alloy (air cooled 50-50) and punched them with 13.5 grains of Unique, they left neat little lead rings at the end of the case mouths and shot for diddly. When I used 4350, they shot ok to about 1800 fps and then petered out while beginning to leave lead rings and lead streaks in the bore. When I used straight wheelweights air cooled, they shot great with Unique and didn't leave lead rings, but I was stuck at 1500 fps. When I tried 4350 I got to about 2,000 fps before the lead rings showed up and accuracy again went south. I kept strengthening the alloy and hitting it with different powders but always came up against a point where the base would rivet and the accuracy would fall off. Understanding that riveting was the issue due to starting against a load, I tried seating the bullet deeper to give it some jump. That worked out ok, but still didn't get the groups I wanted at any speed, with any powder, or any alloy I tried. In retrospect, Taracorp Magnum, water-dropped, with about .015" jump to the throat, and no more than one thousandth total neck clearance and with a high-stearate, stiff lube, just might have worked, but instead I decided to take the lessons learned from the bullet and abandon it in favor of an easier tack....which due to the throat shape ended up being the MP .30 silhouette. Due to the tight tolerances of the XCB chamber, I had to size the bullets to .3105" and turn the necks for a close fit, sort of "pre-slumping" the bullet. I also found I had to nose-first size the bullets, then apply checks and base-first size them to crimp and lube or the metal didn't move correctly. At .3125" as-cast the bullets didn't like getting sized that much, nor were they designed to be until fired, but I made them work and with a little jump, a relatively soft, ductile, 50/50 COWW/SOWW alloy with no additional tin performed admirably. Here are some groups I shot back to back at a hundred yards, without perfecting the workup, at just under 2700 fps from a 23" barrel:

View attachment 5304


Here is a pound cast of the XCB chamber, together with a loaded cartridge and a dummy that had been chambered and removed to show the engraving. I put the pound cast back in for some reason, so that's why it has double engraves on it, but you can see how close the static fit of everything, including the loaded chamber neck, is. BUT.... even then, it was still super-easy to screw it all up and get shotgun-pattern groups if the alloy and powder weren't perfectly selected. I don't seem to have a photo of a loaded MP 30 Silhouette for this cartridge, probably because I shot them all, stuck a fork in it, and moved on to other things.

View attachment 5305

Here's the AM31-190X first as cast, then tapped into the throat unsized at .311", then sized .3105" for the .3108" throat entrance and tapped into the throat. Looks great, don't it? What could possibly go wrong? Well, as I explained, lots. You STILL must get the static fit, jump, run, and bumping dynamic fit just right via powder burn rate and alloy selection or it will find a way to go south on you in a big hurry. View attachment 5306
Ian, have you tried any with pc? In all my playing, the pc completely eliminated any leading and took that issue out of the consideration.
 

fiver

Well-Known Member
#35
correct Bama.
that is why I try to give examples of what has worked for me and try to explain how I got there.
in one rifle I do this, in another I do that.
I start down the trail and follow up on what I thought were the best clues and worked on solving those problems.
once we get more information we start to [just like fishing] develop a pattern and can at some point go ahh let's throw the blue one against the bank and drag It gently through the rocks to the drop off point and they will hit it as it falls along the face or when I lift it off the bottom towards the weed line.
we probably threw our bait in there 100 times or more and kept on putting things together.

tomorrow we show up and we have to start over again but I bet at 10 o'clock we head right back over to that same rock pile and start dragging the blue one in off the shoreline.
after a while we have caught all the 1 & 2 lb fish in that area and start thinking you know it would sure be nice to catch some 4-5 lb ones.
so we have to take what we know and expand on it a bit.
lets move over to the edge of this weed bed and use a blue bait and keep it just down In that area and see what happens, maybe try something a bit blue/green or then green/brown.
eventually we have completely moved away from the blue bait in the rocks and are out 30-40' off shore working a brown/orange bait with an added sliding weight along the edge of a 20' drop off catching some of those 4-5 lb fish.

we are developing another pattern of what works but at another level, the only way to get there is to observe and predict and observe.

so our buddy Bob comes fishing with us one afternoon and we roll up on the drop off and he say's hey man the fish are over there as he is pulling the knot tight on the eyelet of his blue lizard.
and your like well yeah but no let's try this today and you show him your brown/orange bait and explain what your doing.
well he ain't got no brown/orange but he does have a lot of clear silver and orange/black.
well orange is orange so out he goes.
now Bob is having a good ol time hauling in those bass every other cast and your over there doing about as good as normal.
well you just learned something new to add to your baseline of knowledge.
and Bob is just catching fish....
he can't tell you how he got there or why what he is doing is working but he is getting those fish...today.
 

RicinYakima

Well-Known Member
#36
I'm enjoying the thread, guys. While I have no interest in following along, I find it very interesting. Especially as it increases the knowledge of shooting cast bullets.
 

Ian

Well-Known Member
#37
Lets' back up and start with what we DO know for certain, and take a look at what we're trying to accomplish to achieve decent accuracy (consistency, whatever) with cast bullets in rifles....at any speed. This assumes you have a decent rifle to start with, straight chamber, good rifling, good crown, no bulges or restrictions, no outlandish bedding problems, etc.

Rule #1, and there are no exceptions, is the bullet has to exit the muzzle with center of mass being true to the center of form. Whether that actually happens or not is determined by what happens in the first half inch of bullet travel, back at the other end of the barrel, and how good your castings are.

Rule #2 is everything that we can control in making fixed ammunition for a rifle must be evaluated against rule #1.

Rule #3 is you have to get the bullet through the rifle the same way every time. This means consistent bore fouling conditions, and additionally finding and tuning to barrel harmonic nodes, of which there are three movements to consider.

Rule #4 is the bullet has to not only handle launch stress, it has to handle "ascent" stresses too, meaning it must be able to glide on the barrel steel without abrading metal and opening up trailing edge gas leaks. For HV there is land abrasion and torsional stress to consider, and the relax point of the alloy, and bullet lubricants. This is where the alloy and lube matter a bunch.

Rule #5, the bullet base must be square to the crown when it uncorks.


If you make all that happen, the pressure limits of the cartridge is the only ceiling to how fast you can shoot cast bullets accurately in any rifle. "Accuracy" is subjective, but I think we can all assume that one hole is the goal and 1 MOA is a reasonable compromise.

What seems to trip most people up is knowing all the details necessary to comply with Rule #1, most of which is the LAUNCH. This is where alloy, static fit, dynamic fit, and powder all come into play. So let's start there....how to get a bullet into the throat absolutely straight.

First, make a pound cast so you know what your rifle's throat looks like and its critical measurements.
Next, do some thinking and decide what bullet nose profile would best find center. Often, an exact match of the throat with a bullet is NOT the right answer, but something slightly different which can tolerate some static misalignment. Mull over the philosophies outlined previously and ask yourself if you think you can force the bullet to enter the throat straight and keep it straight (like Bama does with his PC bore-riders, or the 165A the way Fiver loads it in a SAAMI .308 throat), or if the entrance is too big and the bullet will have to squeeze too much for that and risk deforming things. Sometimes you need an Eagan MX-30 to fill all the air space and yet have enough displacement areas to go straight up the pipe without crushing the dendrites of the core and allowing it to bend or slump. Sometimes you need a slug of metal to just throw in there and punt out the muzzle and let it take its shape in the barrel (.30 Sil). Think about what's been discussed and see the patterns of alloy requirements for different tasks, i.e. how much skin toughness the bullet must have to self-align vs. smear and crush on one side of the throat, or how much metal will have to move at launch, or how little pressure you can manage to use during the launch to not splatter the bullet completely.
After that, it's all just educated guesses and a lot of observations. There really isn't an instruction manual for picking the right alloy, bullet, and powder for your particular rifle to work at a particular velocity.
 
#38
Ian, this is the best explanation I have seen anywhere in the past! It does point out the vast amount of known unknowns, that this group is working to define and resolve. I hope as we progress that we can maintain an area we’re best practices will be maintained in a clear concise manner so that those who will follow will have a good starting place to build upon.
 

Ian

Well-Known Member
#39
First I want to say I’m learning a lot here and really enjoy this thread.
What I have a hard time understanding is why a bullet like the AM 31-190X will not work. To me it looks almost perfect.
I did notice on the AM 31-188G unlike the AM 31-190X the bullet has a strong taper right at the ball seat area and a little less nose diameter.
Does the nose being smaller and the sharper taper in the ball seat area allow you to use a more ductile alloy that is able to self align? Are you getting any engraving on the 188G other than the foreword most portion of the ball seat area?
The 188G is designed to be seated off the throat and lands slightly, it is not designed to "engrave". In fact, if it IS pushed up until part of it touches the throat, it doesn't shoot as well. The whole concept is that the bullet be loaded with a little slack so it can get moving and self-guide into place in the throat. Self-guiding is something I've found generally to be FAR better at getting the bullet straight than trying to force it to stay on center by reducing tolerances to nil and dancing with safety issues.

This begs another side discussion about bullets which achieve "Rule #1" on the move, or before the trigger is pulled (dynamic vs. static set-ups). A chamber that has a large throat compared to groove dimension (say, .311" vs .308"), will generally shoot best with a bullet sized to throat entrance diameter or a few tenths less (.311" in the case of the typical '06 chamber and many others) because that helps align the back end of the bullet in the chamber neck. .003" is a lot of metal to move without messing things up. The force on the base required to shove a bullet from a stand-still, against a sizing load, plus overcome static inertia and neck tension, is relatively very high, and can be treacherous road regarding Rule #1. So when you're pushing down a lot of metal you need a bullet designed to fold up neatly, an alloy that will allow it with minimal resistance, and a running start.

If you realize that a train can only begin moving one car at a time, due to the tiny but crucial amount of slack in each coupler, the free jump to the throat might make sense in that it removes a lot of the force on the bullet base when it DOES start to squeeze through there. You're applying force to the bullet in stages instead of BAM! all at once and boot it into the bore. This lets you have a bullet that's big enough to fill a big throat and find center on both nose and base, soft enough to engrave easily, yet not be riveted or have it's base shoved to one side or out of square. All you do is match it with a slow powder that gets it moving gently and has a symbiotic relationship with the bullet in the system so the engraving resistance builds pressure to make the powder burn more efficiently and raise pressure AFTER the bullet is already mostly in the throat.

Why not a two-diameter bore-rider for this over-sized throat situation? Well, it will leak gas for one thing, it won't correct itself straight after the jump for another due to lack of angular bearing surface, and it depends on a tough alloy and very close, supported fit to stay straight, and minimal metal displacement to keep its form. Why not the NOE XCB? Well, it's too light for one thing, and it won't pilot right in a straight-taper throat without being poked up against the ball seat, and cannot handle a crooked start. The XCB bullet casts .310" for a reason........a very good reason. The 188G will handle being cast for big throats, fold up easily even with tougher alloy, and the nose profile fits just about any throat there is, easily finding center and bumping to fill up some of the grooves with the nose once it's straight in the bore. It can also handle being powder coated for a variety of bore size variances because the nose can be bumped into a bore-rider in flight rather than beforehand. Just seat it however deep it needs to be to give a little jump, size the bands to fit the throat entrance, cast it from an alloy appropriate for the speed, hit it with a powder that builds and peaks at the right time to get it in the bore straight, and you got it made.
 
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fiver

Well-Known Member
#40
I'm gonna copy and paste an answer to a question brad asked earlier here so we can consider some alloy choices or changes based on what we want to change or why we would change them to get a more desired outcome.

I always thought a 1 part tin to 3 parts [or just under] antimony alloy was just about right.
2 to 1 works well also but nobody is going to make a 6/12 type alloy so a 2% tin and 4% antimony alloy is as far as that ratio needs to be taken.
that one resists shear and twist and bending much better than any other alloy even close to it.
after that a balanced almost 50-50 type blend is best.

then your linotype eutectic blend of the 1 to 3 mix.
that blend just has too much antimony and no grain refiner.
it will take an edge on beating like a champion, but as soon as you try to flex it it just shears away and breaks.

anyway 2/6 casts great as is but the benefits are not there and like
noted the extra antimony has it's own issues.
IMO antimony wash is just the dendrites [hooks] of antimony on the surface of the bullet breaking away then being pressed against the steel.
the wash itself is a good thing, how it gets there isn't.
the abrading is those little hooks scraping and scraping on the steel.
it's why/how lead bullets will clean bits of copper streaking out of the crevices.

the Faux 4/6 type alloy is not an absolute 100% number, but when you look at how the surface is and how tough the alloy really is especially with a bit of arsenic as a grain refiner you can see why I choose it for the throat and nose shape relationships I use it in.
could I cut it in half and use it with the 165?
oh hell yeah, but in what situation would I want to retard that design from moving or flowing?
right.
one where I want to also use a buffer agent and a faster powder to pick up even more speed, but to keep the flow of the alloy in about the same place in the barrel.

to take it a bit further 1/3 alloy and 4/12 alloy are the same basic ratio.
but look at how different they behave.
or do they.
you still have the antimony breaking down inside the lead and allowing things to move and flex.
only one gets 'repaired' as it is breaking down, the small amount of space is taken up by the lead itself sloughing into the crevices.
the other doesn't have that luxury it breaks and breaks and breaks and you then have a fracture line.
so but how does.
so how does the tin stop that?
ahh the magic sbsn chain.
the antimony is still going to try and break.
if you think of antimony as being shaped like this *
and tin shaped like this [ you can see how one of these [ will fit in one of these* with an arm moved.
where did that arm go? well no where really it just got added on to the edge of the [ which was a l before.
but you have a *] tied together now with more *'s .
[*]
*l*
[*]
*l*
that's a balance.
uneven in a 2-1 stacks out differently and the shapes start to change, everything it trying to tie together, so you don't always get a straight chain sometimes it has a half ass circle shape.
*l*l
*.*
or a tin nodule trying to connect more antimony together.
this [would be a 3-1 type] alloy is great for quench cooling because the antimony isn't tied up with the tin it is free to move those star shaped fingers out into the lead further affecting more of it molecularly.

it doesn't really break down it acts more like a support system to the lead so it can act like lead.
it's also why it takes so long for low proportions to show up the final hardness.
everything has to get to it's place more just has more going there so it shows up sooner.
it also explains why the 4/6 alloy doesn't show a lot of gain when it is water dropped, the antimony is locked up and held down by the tin, it has nowhere to go and can't get there anyway.

this is just how I see it working in my head I'm not a metallurgist.