Fit is King - A Practical Journey

[Ian]

how crooked are we talking here
look at the alloy that flowed into the various grooves.
pretty easy to see the 'top' and 'bottom'.

That's a good question. I don't think the alloy flowed into the grooves, but was drawn down by the lands. This bullet was fired through Jackie's rifle (the Savage 1899 that I rebuilt) and has a brand-new .300x.308 barrel chambered with a brand-new Manson reamer and the headspace is just about minimum. IIRC these were seated for a "snick the lever closed" light jam fit, but the bullets came sized, lubed, and gas checked at .310" so there was some neck slop in the chamber. I'll go tap a bullet in and out of it in a minute and we can compare the origin of the land marks on the ogive and see whether the bullet flowed forward or drew lengthwise as it engraved. What I'm saying is I just don't see how it could have enough room to lie parallel on the bottom of the chamber and make the nose that much off center. I think it started crooked, VERY crooked.

 

[Ian]

Here ya go. Can't put much of a rod into the back end of an 1899 but I managed to put a little pressure on it with a short dowel rod and get some faint marks in the nose from the origin of the lands. Pretty much all draw and no bump there, and nowhere to go up or down but plenty of room to go crooked. I tried to line up the noses with each other straight and let the rest fall where it may...looks like the angle between the bullets is about how much crooked the bullet got before it ever moved forward.

 

[fiver]

yep.
you can see the struggle there by looking at how the impressions have pushed back into the different grooves.
almost none in the top groove facing us, and then you get a good side view of it pushing into the one next to it.

i'm only bringing up the alloy movement because of a post i made to Bret in another thread.
you can clearly see how going bigger can create more, and how different wall angles can suck it up better.

of course it most likely doesn't mean anything at 1500 fps. or 50 yds.
but at 24-2500 it's enough movement and unbalancing to cause some issues at 2-300 yds.

 

[Ian]

I was looking really close a the bullet and just shaking my head at how one side of the ogive plowed into the grooves and on the other it didn't touch the bottom of the grooves until past halfway back to the first lube groove.

This is the best physical example of poor dynamic fit that I've ever seen. I've described "the bullet base going sideways at launch" what must be hundreds of times, but a picture is worth more than all of those words.

 

[fiver]

it's too bad those 150's i sent you didn't slip in the barrel, those would be a real good comparison.

 

[Ian]

Oh, and to Bret: a tighter loaded neck-to-chamber fit would have minimized how far crooked the above bullet could go and might have helped accuracy some, but it would just be a band-aid to the real problem which is lack of proper dynamic self-aligning properties of this bullet and this rifle throat designs when combined, plus major contributing factors of way too damned much engraving resistance and no head start (jump to lands).

Think about trying to stand up a full can of soda in a funnel. It will balance upright if you're careful, but any effort to push the can further into the funnel just makes it kick sideways against a flat side of the funnel. The path of least resistance is going to be any which way but straight. Now, think of what kind of funnel shape and what kind of object shape would combine so that force trying to push the object through the funnel would make straight through the path of least resistance. Come up with that, and you have the essence of GOOD dynamic fit.

 

[Ian]

it's too bad those 150's i sent you didn't slip in the barrel, those would be a real good comparison.

Yeah, I know. They shot great in some other rifles I have, though.

 

[Bret4207]

yep.
you can see the struggle there by looking at how the impressions have pushed back into the different grooves.
almost none in the top groove facing us, and then you get a good side view of it pushing into the one next to it.

i'm only bringing up the alloy movement because of a post i made to Bret in another thread.
you can clearly see how going bigger can create more, and how different wall angles can suck it up better.

of course it most likely doesn't mean anything at 1500 fps. or 50 yds.
but at 24-2500 it's enough movement and unbalancing to cause some issues at 2-300 yds.

I think it's interesting in and of itself as it's not something I've really ever seen discussed, much less photographed before. I'm sure it's out there, just not in such specific terms. Makes me think about some issues I've had where over all runout was at a minimum, but I still had problems that seemed to be related to the "runout" I'd supposedly fixed! Lightbulbs man! Love it!

 

[Bret4207]

Oh, and to Bret: a tighter loaded neck-to-chamber fit would have minimized how far crooked the above bullet could go and might have helped accuracy some, but it would just be a band-aid to the real problem which is lack of proper dynamic self-aligning properties of this bullet and this rifle throat designs when combined, plus major contributing factors of way too damned much engraving resistance and no head start (jump to lands).

Think about trying to stand up a full can of soda in a funnel. It will balance upright if you're careful, but any effort to push the can further into the funnel just makes it kick sideways against a flat side of the funnel. The path of least resistance is going to be any which way but straight. Now, think of what kind of funnel shape and what kind of object shape would combine so that force trying to push the object through the funnel would make straight through the path of least resistance. Come up with that, and you have the essence of GOOD dynamic fit.

And again this brings new thoughts into the equation- I know for a fact that not all rifles have perfectly concentric (?) starts to the throat/lands interface. And some erosion from gases can be unequal. I would think all that can play into an imperfect start. Also takes me back to Pope and the false muzzle. He was fighting the same problems.

Kinda makes me wonder how we get as good results as we do sometimes. The possibilities for problems is staggering, and I would think the harder we push things, the more the add up.

 

[L Ross]

While I love the discussion and am finding it enlightening, I have strawberries to pick and process, a range to mow, weeds to spray, a sprayer to unclog and install, targets to paint, branches to trim, wind felled trees to clean up, a drive way to repair, oil to change, a shooting match to oversee, fire wood to split, maple syrup cooking wood to cut and stack, fish to catch, etc.

What amazes me is that I know from this forum how busy fiver, Ian, and Bret are. They make my meager efforts seem inconsequential, and yet not only do they have time to ponder the imponderable but also come up with solutions and implement them.

I am just glad I stumbled upon a couple of combinations that work well enough that I can enjoy shooting when I take the time to do so. Probably why I like .22 rimfire and off hand shooting so much.

 

[todd]

best wishes Mrs Dimner!!!!

 

[Dimner]

Thank you greatly. She is doing great today. She has a spine stimulator do-dad type thing implanted. Comes with a remote control, an app for her phone, and a wireless charger puck. I need to figure out how I can rig it to power her down in uhh... certain situations.

 

[Dimner]

when i talk about the 'system' i'm including alloy and powder speed.
alloy and design also go together.
design/alloy, powder speed, and jump go together.
that's a system.

god i wish i could pull up that damn 3 post post i put up over to Jay's place.
it walked through alloy and design choices and why they worked together under the same circumstances.
i'd also love to have that buckshot shot shell workup data i posted throughout the process of working a load over with different alloys and speed changes.
that took me over 2 months to put together.

Fiver,

Two quick questions.

1) When you say 'jump' I'm assuming you mean the standard reloading definition of the distance the bullet is seated from the lands? Or is there different cast bullet definition that applies here?

2) 3 post post i put up over to Jay's place.
Has anyone ever tried to find this via the way back machine? I'm not sure what Jay's place is, but if someone PMs me the details with dates, I can try to find it via the way back machine if no one has tried.

 

[Dimner]

Ok Dimner, let's update your posts again.


Dynamic fit is the moving relationship between the contacting surfaces of the bullet and the inside of the barrel. It ceases to matter once the bullet has departed the muzzle.


Try this:

"Broadly, fit is the relationship of measurements between the bullet itself and anything that touches or will touch it inside of the gun, with the emphasis being on tolerance reduction and exact replication. Regardless of the many methods by which the bullet can be fit to the gun, the end goal of any specific mechanical fit technique is starting the bullet absolutely straight into the barrel so that it flies true when it comes out of the muzzle. Bullet fit can be broken down into two categories: Static Fit which is how the bullet shape relates to the firearm at the moment it is about to be fired, and Dynamic Fit which is the moving relationship between the contacting surfaces of the bullet and the inside of the barrel, from chamber to muzzle."

Some questions, so I can make this clear for the simple folk such as myself.

tolerance reduction and exact replication
For this term, do we mean the exact replication (repeatability) of our desired fit each time a round is loaded? I just wanted to be sure I understood. .... oh, I just read your later reply to fiver. I'm going to add a bit of simple man language in there.

...tolerance reduction and exact replication. Exact replication being the repeatability of our desired fit each time a round is loaded.​

Static Fit which is how the bullet shape relates to the firearm at the moment it is about to be fired,
Doesn't case prep also impact static fit? Or is it minimal enough that we do not really need to include it in this basic definition?

Or just use what you have on hand and make a robust, dimensionally accurate pound cast.

I'm unsure, how to poundcast a semi auto. An AR, I guess I can remove the barrel from the upper. But for a garand, I'm not sure how I would have to leave the barrel on. I'll do some google work on semi auto pound casts. Perhaps, I just pound too hard

Here's another way to make a Marlin with the cathedral throat work and it will blow most people's minds: forget the nose and steer the bullet from the back end, that's what that long neck and small chamber neck clearance is for.

Back end steering and cathedral throat, I'll add those to the list to expand on. Is this the backseat driver fitting method? ;-)

3⁰ included angle, straight taper nose

I need to start gathering these terms and adding them to the bullet profile section. also, to add a list of bad happenings to look for (flame cut reminded me. Alloy flowing into lube grooves, is this bad or good or situation dependent?

I know for a fact that not all rifles have perfectly concentric (?) starts to the throat/lands interface.

Amen to that. It took alot of cussing and frustration for me to learn that the first time. Simple to assume everything in that chamber and throat is exactly what you see in those chamber drawing diagrams. My very first pound cast, I can say with certainty, included some very frustrated pounding. Once I saw the result, it seemed like the most trivial fact that I had missed.

 

[Bret4207]

As far as case prep and static fit, yes, the case is part of it.

 

[Ian]

Yeah, the case is a BIG part of it, really big. So is headspace, ejector plunger pressure, gravity, etc. Concentric neck, neck tension, neck wall thickness, chamber neck clearance, state of neck anneal, leftover bell or crimp, case trim length, all matter. We'll get to that part later. Maybe this for the definition?

Static Fit which is how the bullet shape relates to the firearm system at the moment it is about to be fired

You got it about "replication". Doing it the same every time. Edit as you see fit for clarification.

Pound casting an AR is the same as any other rifle. Easier if you take the upper off if you need to tap the extra-long-seated pure lead bullet into the chamber, just use a non-marring punch to lock it up. After upsetting the slug in the throat, unlock the bolt by pulling back the charging handle until it fully rotates, then put your slugging rod back into the barrel and "pogo" the rod on a block of wood while holding pressure back on the charging handle. It should pop loose. Don't forget to fully anneal at least the top half of the cartridge case and fill it about halfway up the neck with a firm alloy like wheelweight metal. The neck and shoulder needs to be fully annealed so it will take the form of the chamber in the front end, there are useful measurements to be had there. Also, put a very light film of grease in the chamber and throat before upsetting the casting or it will be a bear to get out again. Don't forget to clean the grease out thoroughly before shooting it again!

 

[popper]

how I can rig it to power her down in uhh... certain situations.
Let me know if you figure it out. Her sister has some real health problems. After they talk I get to try to wind her down.
Note that the 'tails' of the lands also go forward.
Also note that the lube grooves are not perpendicular to the bullet axis any more.
I don't know what load Ian used but I have wondered how fill effects ignition. In respect to pressure on the base. we expect base pressure to be the same across the base but is it? If powder lies in the case and burns on top, is pressure higher at one part? Definitely would cause a crooked base and bad start. If the base is not entirely in the neck, bent bullets?
I have a RD style mould I modified from the original. I did find that if it has a step like the 041 it is much more accurate as the nose gets centered in the bore without jamming the lands.
ejector plunger pressure definitely should create an off center problem.

 

[462]

ejector plunger pressure

ejector plunger pressure definitely should create an off center problem.

As a matter of discussion, and disregarding the myriad factors that relate to cast bullet accuracy, or inaccuracy, would, then, a Mauser-type action have a discernible edge?

 

[RicinYakima]

As a matter of discussion, and disregarding the myriad factors that relate to cast bullet accuracy, or inaccuracy, would, then, a Mauser-type action have a discernible edge?

Yes, I set my match Springfields up so that the rim of the '06 case floats in the hook of the extractor. Not a problem as long as the chamber is smooth and you keep pressures down to less than 40,000 CUP.

 

[Ian]

Hey Dimner, where ya gonna draw the line? LOL.

I already explained most of what you want to put in your fit article in the Basement Articles. It took nine articles to cover the whole SYSTEM and they are fairly brief, as in 2-3 pages each. They need to be edited and expanded considerably but I don't have the editing capability or, frankly, the time or inclination right now to do it. The gist is there.

My recommendation is to give a nod to the system (neck tension, mechanical concentricity of the case and chamber, and that sort of thing) but focus on the bullet. The simplest thing to do is define static fit and the terminology and then put a drawing and brief description of each fitment technique with notes about certain critical particulars.

Then, start this whole thing over and let's get into DYNAMIC fit as a separate topic because it literally involves everything. Put in short, dynamic fit is all about creating a good relationship between powder, alloy, and bullet design and mostly applies to fixed ammunition. Breech-seating (or muzzle seating, for that matter) takes almost all the dynamics out of the equation, which is why those methods can be so so effective to making small groups.

As I have time I can make drawings like this one for each method. Some will require two or more frames to make sense.