Casting Session, NOE 310-165-FN (30 XCB)

[Bret4207]

Ian and Fiver have put sooooooooo much into these last few posts. "Fit" covers such a wide variety of parts and pieces. I have now begun to rethink parts of static fit I hadn't considered before and parts of dynamic fit that I'd realized were players, but not in the same way Ian lays it out. If could make a suggestion to Ian, Fiver and whomever else has gone into "No Mans Land" and done well, you have the start of a truly in depth discussion on not just "why" things work, but the "why" of how alternatives work in different set ups. IMO, that is a massive leap ahead regardless of what velocity you are shooting for. I think this part of the thread deserves a place of it's own where it can be hashed out, perhaps as Ian suggests with a pictorial guide, and retained for a long period. Maybe you all did this on the other site, but what I'm reading here has already modified my refusal to consider Bhn as more than an advertising gimic for the most part. I admit that my years of seeking success via the "HARDCAST" route left an extremely bitter taste in my mouth, but now I'm starting to see where reaching a higher Bhn number VIA A SPECIFIC PART OF THE ALLOY can be a help as you increase pressures. I won't say I agree with some of the theory on what happens inside the case, but that may just be a function of the descriptive terms used. Or, I could just be wrong! I think whats laid out above applies to the broad spectrum of getting cast to shoot well and not just to the high end stuff. I'd like to see this get it's own thread or become it's own sub-section and be transferred there. I think it's important enough for that. I'm not tying to give anyone a swelled head, but this reminds me of some of Felix's dissertations where he'd give a logical answer to why something we "knew for a fact" was so much horse puckey.

Respectfully Submitted, Yours Truly.


Ian- 45 2.1, haven't thought of Bobby in a long time. I had a long drawn out PM session with he and Starmedal Joe on the 6.5 Swede. I eventually figured out what they were doing but it was like pulling teeth from a fully conscious Bengal Tiger with a hangover.

 

[CWLONGSHOT]

We have all read for years and years from various authorities that 1800 was the threshold for accuracy with cast in most Rifle calibers.
Some experiment with coatings and alloys and have been able to achieve better velocity.
But at the same of aggravation, there is little I need to shoot with a cast that requires more than 1800 FPS. IF I had to have more power just take the black powder theology and use a bigger bore/ heavier projectile at same 1800 FPS. Only other I can think of is get game Closer.

Last choice IF more is still needed, I’ll load a jacketed bullet.

At least that’s this mans opinion.

 

[Ian]

Whatever makes you happy, CW.

Bret, I'm working on it, actually BEEN working on it. This time I want to put together Basement Article #9, and have it peer reviewed and polished, put up for discussion, edited some more, and stuck in the read-only section for posterity. Here's the challenge, though: Dynamic Fit is actually at least a semester of graduate studies. I'm not kidding. If I put it in lecture form with all the chalkboard drawings and notes, the content would literally be like a full course in, say, binary phase graphs. Fiver could explain it in a few sentences, but only those who had already taken the course would fully understand what he meant, and those who are new to the concept wouldn't have a clue what he meant.

Alloy and BHN. Yes, well, you have to consider both. You need a certain toughness (BHN) to do certain things, but then you get into dynamics again and different alloy compositions having the same BHN (static) number will behave differently in motion. Water-dropped 50/50 alloy is hard, like 18-20 bhn after aging, but work-softens instantly when squeezed. Think of expanding spray foam, it's very rigid when cured, until you squish it and break down the internal bubble structure. It may spring back to its cast form when you let go, but it will be squishy throughout and not rigid anymore because you crushed the microstructure. The crystal lattice structure of lead (modified and refined through the addition of antimony, tin, copper, arsenic, etc) can be manipulated to do different things for....or against you. That subject alone is a six-week course, but is a super-critical part of the dynamic fit equation and choosing an alloy that will work best with a certain bullet nose shape and throat shape combination. The various behavior characteristics of similar-BHN alloys under stress and flow is why we can say use the MP 30 Silhouette in the .308 Winchester SAAMI throat with water-quenched 60/40 alloy and give it 20 thousandths distance off the lands, OR use the NOE 30 XCB bullet (different nose shape, doesn't self-align as well with jump) and seat it to touch the ball seat of the throat, but use an alloy that doesn't crush and break down as much under pressure (something near #2 alloy). The 30 Silhouette can be cast of a weaker alloy that draws better, sized really large to take up all that slack in the chamber neck to help guidance (IOW bigger than throat entrance), but still fold up like an umbrella (due to its shape and alloy composition) and draw down through the throat without creating excessive resistance that would cause powder pressure to bump too high and rivet the base before it gets into the throat.

You discover these things by trial and error, mostly. Like Fiver telling me to bump the tin for my .223 bullets and back off the lands a little as I increase the powder charge. Why did he say that? Well, if I hadn't backed off the lands at higher pressure, the bullet was getting hit too hard under too much resistance as I increased pressure/velocity and was starting to rivet and distort, ergo groups went to hell. Toughening the alloy and making it more resistant to breaking down by increasing tin to work with the existing level of antimony actually made the problem WORSE, but backing off the lands and letting the bullet have a head-start on the throat mitigated that. But when you back the bullet away from the lands/throat to give it that running start, the alignment is going to suffer because we don't live in a perfect world and something without full guidance is going to go wherever it wants to, so creating a tougher alloy (balanced tin and antimony, in this case, or it could be half a percent copper, or just powder coating what I had to toughen the skin) counteracted the tendency toward slight misalignment with the head-start/jump and allowed the bullet to handle banging into the ball seat in probably not a perfect, dead-straight alignment, correct itself, and get perfectly straight as it went into the bore. So I had to change two things at once to maintain the same group dispersion as I increased the powder charge. See how complex and inter-related this stuff is? How do I capture the essence of dynamic fit clearly in 1,000 words or less?

I learned a lot about alloy dynamics and fit from 44Man (James Miner). He wrote a lot about having a little wiggle to the cylinder at lockup, using water-quenched straight wheelweight alloy, and using a WFN or at least RFN bullet that did NOT have an abrupt diameter change between the base of the nose and the front driving band. He hated the "Keith" style SWC because all of the alignment force was put on that weak, abrupt leading edge and it would collapse rather than guide the bullet straight in the forcing cone. He needed a tough yet flexible alloy and a lot of surface area on the nose to take the stress of bumping the cylinder (and back half of the bullet) into perfect alignment as the bullet was transitioning into the barrel. If the bullet was slightly crooked and got smeared a little more on one side than the other, the base wasn't going to exit the muzzle perfectly squarely and the bullet would wobble in flight like a poorly thrown football (my analogy). This same concept applies to rifles, particularly autoloaders where we do not have the luxury of a hard jammed, fully-supported, no-tolerance static fit.

 

[Rick]

44man hated the concept of inline bored throats on a revolver, spent years putting down Freedom Arms in no small part to their revolvers being inline bored. However that is the best method of locating and boring revolver throats if done on quality machinery by a skilled machinist.

Colt and S&W and to a lessor degree Ruger have a good deal of "wiggle room" built in because the throats aren't as accurately aligned with the centerline of the bore, a cheaper easier way to achieve the same thing.

 

[Bret4207]

CW- I understand what you're saying, and honestly I may never get past 18-1900 fps myself. But the theory applies on down into stuff like the 38S+W popping a 200gr bullet out at 600 fps. That's what I want to look at- the WHY of all this and the ways people get a hunk of lead to fly right.

Ian- I'm actually following the line you're talking. I don't understand all of it, but I'm getting the idea. More pressure requires tweaking in directions I've never thought about before and there's more than one direction to take the tweak. That's the fascinating part for me.

The idea of the self aligning bullet goes back a long ways. I suppose what should amaze us is the way in many guns a Keith SWC will shoot so good. 100 little variables all coming together!

 

[Ian]

Bret, think of it like this: Job one to achieving cast bullet accuracy at any speed is getting that bullet started into the barrel absolutely straight. Because of the limitations of fixed ammunition, tolerance is necessary. Tolerance gives the bullet room to get crooked as it starts into the throat. So we have to find ways to "herd" that bullet along and mitigate everything that's fighting it going straight as the bullet slams through the throat.

Rick, I can have a 6mm BR rifle put together with a slow-twist barrel and no neck clearance for about $5,000 and ream a bump die with the same reamer used for the throat and not have to worry about factory slop in the chamber or alignment issues. It would shoot boring, tiny groups all day, but it would cost three times what my standard, 10"-twist LR-308 did and would suck for hunting pigs. I can hunt pigs with wheel weight alloy at jacketed speeds with sub-MOA accuracy and reload for pennies with military brass having nothing more done to it than a trim to length, flash hole deburr, and primer pocket uniform. Cheap and effective.

Point being, there are diametrically opposed methods of achieving the same ends. Some cost more than others. If I want to make the most out of my Model 29, I use James's or Elmer's way of fitting (both work for me). If I were to compete, I'd probably have join the equipment race.

 

[fiver]

now I read some more responses and kind of lost the train of thought I had chugging along.
so I;m gonna summarize for now and then we can work on it some as we go along.

here is how I'm looking at things at the moment.
at one point I had figured out 2 different ways of do this and this and you'll get there.
now I'm closing in on 4.
when I generally talk about one way or the other [of the 2 ways] I reference 2 different bullets.
one of them gets there similarly to how Ian generally describes things, except,,, he is getting there with a similar alloy and bullet design.
when I say similar it has certain attributes that are similar, only with more pressure relief areas on the bullets drive band area.
okay.
think about close and similar and think about similar and opposite pressure spectrums.
not in high and low pressure but in opposite amounts of different speeds of pressure.[application of where in time]
when I talk about where a bullet is in time I'm talking about application of distance and pressure.
the whole discussion about neck tension and lack of tension all fall into line with this discussion.
in the other thread where most everyone chose a jammed bullet and fast powder speeds.
except for one person that followed my XCB thread then went out and also put some lead down range at 24-2500 fps.
[why did most everyone choose a faster powder speed? was it for one and only one reason?]

there is a couple of lessons here, manipulation of time/distance are important, especially when your trying to trick a glob of putty into a pipe and out the other side again.
it isn't as simple as push here and push there or try to get the powder to respond into a state of 100% burn.
I seen DR. Mann referenced earlier, he done a lot of work back in his time and reached some conclusions that made perfect sense.
none of it applies here,, none of it.
except [rright always that except thing] it lays a groundwork for how important getting a bullet into the barrel straight really is.

 

[Ian]

Explaining this is a bitch, ain't it? I think I understand enough to begin to explain it, but not in a super-succinct manner. Maybe pictures and drawings will help.

I'm one that said jam it in theory but actually am doing things like loading PC'd, soft bullets at 2400+ fps or 2550 with I-4320 .050" off the lands because I have to so's they fit the magazine. Some things just work out and I don't ask too many questions.

Don't forget Buffer....that's yet another modifier for the launch when you got too much base-band chowdering going on and need to absolutely blockade the hot gas behind the gas check.

 

[Bret4207]

There are other variables in play outside what you 2 are talking about. For instance, define "jam it in". This is like defining "hardcast". My version of "jamming" is just a smidge of a feel of the bullet contacting the leade as the bolt closes. I can easily withdraw a loaded round and on inspection will see just a hint of where the lead and steel contacted. For someone else, it might mean JAMMING the frickin' thing in there where withdrawing a loaded round is an iffy proposition. Variables!

I like the idea of time/distance/pressure and adding it to dynamic fit issues. I thought about this many years back when I was assigned to explain why short barreled guns had more flash with some loads than others at our Academy. It's stuck with me for 30 some years, trying to picture the flow of things as they progress.

 

[fiver]

to get a hard jam you need to also manipulate the neck tension, or 'over fill' the case with powder.
it has to hold the bullet in place and create enough friction to overcome the engraving forces.

a jam against the rifling is different.
if it's done in conjunction with a low enough neck tension there isn't any sort of engraving done your just touching one [or two] point of the bullet against the steel of the barrel.
if you have a tapered interference fit between the shape of both the bullet and the throat you can get almost 100% of the bullet touching steel.

if you notice so far nothing has been said about bullet diameter.
that is another piece of the puzzle, and really only comes into play as far as initial fit if it is capable of touching metal in one point or another before moving forward.
when the bullet does move forward that is when the engraving and metal movement really begins.
you can have a bullet touching steel and room for it to move forward [jump] before the funneling into the tube really begins.

the key is where does that metal go when it does start moving.
in one case it presses inward then gets a break then starts again [rifling] the nose of the bullet right before the full diameter [drive band area] takes a pounding and shape and diameter right there is the critical portion.
in another shape the throat starts pushing all of the shape rearward when the bullet hits the end of the funnel.
it actually starts slightly changing the shape of the bullet not just stressing the sides.
it holds the bullet in alignment because there is nowhere else for it to go no rattling around so much as it were.
that is the point where you start to maybe go hmm my alloy might want to either take up that bashing, or it might wanna be able to flow a little easier to avoid being chunked up when it's trying to funnel itself into it's new shape.

now.

 

[Ian]

With respect to dynamic fit, I have been using the term "Jam" to mean anything from just the lightest contact to rammed up the throat so hard it sets the bullet back in the case neck. There is some, but very little difference to the starting resistance that I can measure on paper or with a chronograph between hard/soft jam versus say .020" away from the first point of throat or rifling contact. The more closely the bullet nose matches the throat shape, the less the amount of jam pressure matters.

 

[Ian]

aaannnd a double. knew that was gonna happen a lot on this thread.

 

[Ian]

Here's my original article from years ago, it needs updating but some of these concepts are there. It barely scratches the surface and doesn't speak nearly enough about metal moving and pressure rising on a play-by-play basis. The article #1 did more of that IIRC.

Article #4: Cast bullet fit and design

Disclaimer: The following information is the product of my own meandering experience and includes a few original ideas and concepts of my own and some that others have been kind to share with me, and is always subject to change as I learn more. It is in no way intended to be the last word, or...

www.artfulbullet.com

 

[358156 hp]

Fascinating. The facts behind the advice we've all given and received over the years. Things that we know work, but at least I didn't realize until seeing it spelled out like this, the way things work, and how. Ians sig line has much more meaning to me now. And I haven't shot cast in rifles for ages. None of this is strictly rifle info either.

 

[Bill]

I haven't needed 2500 fps for any shooting I have done, most are 14 to 1500 fps, lots of them (empty gc boxes everywhere), but I don't care if you shoot 1000 fps or squirt blobs at 3000 fps this thread is golden, we can all learn a ton from this, thanks guys

Bill

 

[Ian]

My great aunt's father-in-law coined that play on words to describe the nuance of technique, usually as he was demonstrating a difficult task in a way that made it look easy. He was also fond of observing when appropriate that someone has "got the Touch", meaning rare, natural talent or hard-earned mastery.

 

[fiver]

I'm gonna reference my post #90
with this addition.

the first Jam fit I refer to is how I treat my 30-30 lever gun, my K-31, and one of my 308's.
neck tension and a roll crimp is useful here.

the second method against the rifling just touching and kind of floating with low to medium neck tension is how I do my XCB rifle, my 30-30 bolt gun and my AR-30 with the XCB bullet.

the third [yes there is a third] and another one that I use is the use of the body and the nose to line the bullet up in the leade and the rifling.
this is the one I use with the 165-A in the AR-30, the wifes 0-6 with the same rcbs bullet I use in the 30-30 lever action, and in my 03A3 when I want to go fast with it.

plus one more where I just use the forward section of the bullet to help snug things into the leade and the nose of the bullet doesn't touch anything until it hits the other side of the throat.
this is basically how I do my 223 AR rifle, and oddly enough my 358 win, these both use a high end jacketed load right out of the book just substituted with a cast bullet.
[but not the same alloy]

remember all of these [except the K-31 and the first 308] are going 2350 or more FPS.
the point is I don't just concentrate on trying to shoot jacketed speeds.
I make my own jacketed bullets with about the same amount of work as casting lubing sizing and checking takes.
I don't need to shoot everything fast, and speed without accuracy means dick to me.

anyway those are some examples of the workarounds and where I apply them.

 

[Intheshop]

Velocity helps a LOT in varmint hunting when you don't have the luxury of "ranging",and you want explosive terminal ballistics.

Mention "hunting" and cast however,and it automatically means deer.... least that's my impression. Where it's a HUGE target compared to say a crow. And having a slower,larger bullet makes good sense. Two completely different applications,that can't be painted with a 4" brush.

Velocity at the bench means less time for wind to play it's number.

 

[Intheshop]

I define a hard jam as..... you ain't extracting a loaded round without using a stick( poking a cleaning rod from the muzzle).

A hard jam is but one,though it comes with a cpl other effects.... way to keeping the case "quiet" during the critical phase of the launch.

 

[Intheshop]

"Speed is fine,accuracy is final"

Wyatt Earp.

Saw this the other day googleizing 1911 ballyhoo.... it's a reference to action shooting,but sort of fits in with cast rifles as well?