Has anyone ever have brass not strech in a simi-auto AR-15?

[Blue68f100]

Back ground: I have a 224 Valkyrie that I built about a year ago. Shilen 1:7 twist, 28" SS blank, finished to 24", rifle length gas system. The reamer was a piloted Clymer that I special ordered. Did my own barrel machining and set the chamber up at min spec. Adjustable gas block to fine tune the action.

All the brass is still at min trim length (1.590") after 5 firings. The only ones that have grown are the ones where I pushed them over the edge with hot loads. Pressure bolt markings on base . But those are only 0.003"-0.005" over the trim length.

The brass I'm using is Starline, which came in at trim length. The necks have been turned to even up the wall thickness. But that's all I've done to the brass besides my normal prep work. I have 5 firings on this brass, anneal every cycle. Using Redding Deluxe dies. I've only had a hand full of the brass fail due to loose primer pockets. When I size the brass I'm only moving the shoulder back to min. I can clean up the fired brass up and it sets about 0.002" high in my chamber case gauge, made with the same reamer as the chamber. So I'm not getting a lot of stretching to begin with.

Has anyone ever run into a AR-15 that does not stretch the brass? It's a welcome surprise but not what one expects.

 

[FROGO207]

Sounds like stacking tolerances worked in your favor this time. I never seem to get that. Just be grateful I would say.

 

[243winxb]

Soon or later brass needs trimming. Keep checking.

Your chamber and sizing die diameters must be a close match. Minimal sizing. A good thing.

I found a fired 223 case may get shorter head to datum, plus shorter trim length. The case body expands outward, pulling the shoulder back, along with trim length. Mostly in light to midrange loads.

Measure your fired brass before and after sizing. I see my fired brass gets shorter, sized gets longer?

Hows the accuracy? Any targets to show?

 

[Rule3]

It was my "understanding" that working the brass, as in full length sizing was the reason brass "grew" Not so much the actual firing or dimensions of the chamber etc
Brass that is "neck sized" only does not grow very much. Just adjusting the shoulder doesn't seem to work the bras that much either.

I am sure it is all debatable

 

[Blue68f100]

The accuracy has been kind of hit or miss. I've found some combo that it does not like at all. And some that shoot very well. I built this looking for a cheaper round to fire at 200-300 yrds. What I have found it is it likes the more expensive bullets which defeats the purpose, with a few exceptions. I have come up with a 52 gr, 75 gr and 80 gr that shoot very well in this gun. Below is target I shot yesterday narrowing in on a load for the 80 gr ELD-M bullets and Varget. I found that it also likes the 52gr SMK w/TAC. This is my cheapest combo to load. These rounds are loaded just 0.003" off the lands with only half the neck being used. I single shot these on the concern the bolt slamming home may dislodge the bullet. I've tried about 5 different bullets and 4-5 different powder combos.




My 200 and 300 yrd range is shut down for the moment as I'm having some trees harvested. So in a week or so they should be finished and I can test again at the longer distances.

My dies set is a FL set not a Bushing or Neck sizer.

 

[Rule3]

. When I size the brass I'm only moving the shoulder back to min. I can clean up the fired brass up and it sets about 0.002" high in my chamber case gauge, made with the same reamer as the chamber. So I'm not getting a lot of stretching to begin with.

Has anyone ever run into a AR-15 that does not stretch the brass? It's a welcome surprise but not what one expects.

 

[Swampman]

My guess is that the lack of stretch is probably due to a combination of a tight chamber, 30 degree shoulder and reasonable chamber pressures. Wouldn't surprise me if you're keeping the gas dialed back as well.

 

[jmorris]

If the brass fits the chamber exactly and you don’t move it excessively to resize it. It can stay very close to the same dimensions.

I have some combinations that I can reload and fire the same piece of brass 3 times without sizing it at all. Yes, that includes enough neck tension to hold the bullet in place, without sizing.

 

[Swampman]

If the brass fits the chamber exactly and you don’t move it excessively to resize it. It can stay very close to the same dimensions.

I have some combinations that I can reload and fire the same piece of brass 3 times without sizing it at all. Yes, that includes enough neck tension to hold the bullet in place, without sizing.

In an AR?

 

[jmorris]

In an AR?

Nope but I don’t own any AR’s that won’t run on ammunition loaded to maximum dimensions, that way they can’t choke on factory ammunition manufactured within the allowed tolerance.

Not what the OP has done.

The reamer was a piloted Clymer that I special ordered. Did my own barrel machining and set the chamber up at min spec.

Some of my chambers are going to be “looser” than others. The earlier statement was with chambers, die and brass made for one firearm. Doesn’t mean it couldn’t be done with an AR but I have enough stuff to keep up with than what box of ammo goes with what AR barrel/bolt combination.

Edit: actually I do have one AR that is the only firearm I own in that caliber and my reloading dies are set to that chamber. I am still using the 100 cases I bought in that caliber (actually only 50 of them) despite having fired it more than a thousands times, they were trimmed once to start with. I wouldn’t begin to assume they would function 100% in different firearm chambered in the same caliber though.

 

[ms6852]

If it is brass that has been fired more than once it could be that the brass has gotten hard and you might have tight chambers. Just keep and eye out for cracks when you full size. It it began to split might be time to anneal the brass to make it soft again. I've noticed on my AR that I normally can shoot it a couple of times before I have to anneal it.

 

[Blue68f100]

I anneal every cycle, so the brass is always in the same state. My ammo fits all my (3) AR's with no problem and any of my neighbors/friends too. All sized down to min spec.

 

[ms6852]

I anneal every cycle, so the brass is always in the same state. My ammo fits all my (3) AR's with no problem and any of my neighbors/friends too. All sized down to min spec.

Looking at you shot group , nice by the way you have found your node. I really don't think you have an issue at all , it's like fire forming brass. I would just measure and inspect if for every load all the time. How do you like the Valkryie? My brother is thinking of a new build either 6.5 or the Valkryie and I really have no experience with either. I for one never like to recommend or make decisions based on ballistics alone.

 

[Blue68f100]

I'm finding the Valkryie has a smaller nodes to work in vs the 6.5CM. So it's a lot more work in finding whats the best combo. Also there is no Match quality brass available for the 224V, only choices are Starline and Hornady. I've been using Starline Brass. But have not sorted the brass by volume. I seam to always get at least 1 round the velocity is way off my target velocity, 50-75+ fps. Like I said earlier I was looking for something a little cheaper to shoot vs the 6.5 CM. All depending on what bullet you choose, in a lot of cases the heavier 224V bullets are more expensive. So far these 80 gr ELD-M w/Varget have produced the best consistent groups and the bullets cost around $0.21 each. I've bought the 140 ELD-M for the 6.5 CM at $0.28 ea. But lots of the better bullets for the 224v run in the $0.35 ea range. Which makes it more expensive to shoot.


The 6.5 CM will out shoot the 224V in my book. If I had to choose between the 2, I would go with the 6.5 CM. The 140 gr ELD-M bullets and H4350 are a combo that's hard to beat. Now if you want to hot rod the 22 cal for a varmint load the 224V can push a 52-55 grain near 3500 fps fairly easy. But wind pushes the light bullets around pretty good.

 

[fguffey]

found a fired 223 case may get shorter head to datum, plus shorter trim length. The case body expands outward, pulling the shoulder back, along with trim length.

How is that possible? One day you are going to get tired of kicking the can down the road; and then What? I think you are going to have to start thinking.

F. Guffey

 

[243winxb]

How is that possible? One day you are going to get tired of kicking the can down the road; and then What? I think you are going to have to start thinking.

Mostly in light to midrange loads.

 

[fguffey]

243winxb said: ↑
Mostly in light to midrange loads.

I found a fired 223 case may get shorter head to datum

The case body expands outward, pulling the shoulder back, along with trim length. Mostly in light to midrange loads.

How does a case get shorter from the shoulder to the case head when fired?

"The case body expands outward, pulling the shoulder back"

Again, how is that possible?

F. Guffey

 

[ilbob]

I reloaded a fair amount for my Mini14. i checked the brass after it went through the sizing die with calipers. Rarely did I need to trim one.

 

[Orcon]

I'm finding the Valkryie has a smaller nodes to work in vs the 6.5CM. So it's a lot more work in finding whats the best combo. Also there is no Match quality brass available for the 224V, only choices are Starline and Hornady. I've been using Starline Brass. But have not sorted the brass by volume. I seam to always get at least 1 round the velocity is way off my target velocity, 50-75+ fps.

This has been my experience as well. Additionally, my most accurate loads have been in the low to middling range of the load map.

To answer your original post though, I have a Larue 223 Wylde barrel that produces no discernable case growth. I cannot say why but I think it has something to do with how they chamber the barrels, fired brass has light, helical carbon stripes on the body that makes me think that they are semi-fluted.

 

[Swampman]

How does a case get shorter from the shoulder to the case head when fired?



Again, how is that possible?

F. Guffey

He already explained it in the post you quoted, but I'll try again.

I guarantee that brass gets shorter when forming regular .257 Roberts brass to the 40° shoulder Ackley Improved version.

My guess is that the brass being expanded to fill out the shoulder and area of reduced taper pulls the neck back towards the case, making the overall length shorter.

I have several hundred Winchester +P cases for that rifle, all formed from virgin brass and with some fired at least six times. None have ever been trimmed and the majority are still below SAAMI minimum length.

 

[Varminterror]

How does a case get shorter from the shoulder to the case head when fired?

Again, how is that possible?

Only way it is feasible:

1) Cases are under-diameter for the chamber

2) Max internal pressure is sufficient to blow the case walls outward, but not sufficient to hold the shoulder forward

 

[fguffey]

2) Max internal pressure is sufficient to blow the case walls outward, but not sufficient to hold the shoulder forward

How does a case get shorter from the shoulder to the case head when fired?

Again, how is that possible?

I am the fan of the datum; although there are no tools that are labeled and or identified as a 'datum based tools' most of my tools are datum based.

When I ask how a case gets shorter from the shoulder to the case head when fired I am not confusing the shoulder with the neck. The length of the case is measured from the end of the neck to the case head. The measurement taken from the shoulder/datum to the case head does not determine case length.

"Hold the shoulder forward"? We have members on this form that swear the impact of the firing pin shorten the case .005"+ (from the shoulder/datum to the case head) when it drives the case forward and I ask "why isn't that a bad thing"?

2) Max internal pressure is sufficient to blow the case walls outward, but not sufficient to hold the shoulder forward

You guys are going to have to decide "what it is"; the pressure inside the case locks the case to the chamber wall. When the case is fired and the case is locked to the wall of the chamber the shoulder does not move. The pressure inside of the case blows the case our and forward meaning the old shoulder became part of the case body and the new shoulder is formed from the neck of the case.

What does some of that mean? It means the case body from the datum/shoulder to the case head gets longer and the neck gets shorter.

And then if there was any truth to the firing pin story and if there was any truth to the case locking to the chamber and the shoulder was against the shoulder of the chamber the case would stretch between the case head and case body ‘by how much?’ My rifles start with clearance as in the difference between the length of the chamber from the shoulder to the bolt face and the length of the case from the shoulder to the case head.

If my chamber has .005" clearance and the firing pin shortens the case .005" between the shoulder and case head the stretch between the case body and case head would be .010".

So I asked 243Winxb to explain.

F. Guffey

 

[Varminterror]

My guess is that the brass being expanded to fill out the shoulder and area of reduced taper pulls the neck back towards the case, making the overall length shorter.

That isn’t an answer to the question Guffey has (repeatedly) asked.

It’s well understood how and why cases get shorter - overall length shrinks - as the case expands to fit the chamber.

The proposition here - which Guffey challenged - was that SHOULDERS were moving back from firing.

What @fguffey is (mistakenly) promoting is that case expansion will always create sufficient grip on the chamber wall, preventing shoulders from ever moving backwards, and further, any pressure sufficient to move the case wall is sufficient to move the shoulder - neither of which are universally true. In standard pressure loadings for modern bottleneck cartridges, yes. For low pressure loadings where the case neck might not even seal the chamber, no. When you see soot all the way down the case wall, you know you’re not sufficiently expanding the case to seal against the chamber wall. Pressure is force applied over an area, there’s much greater area of case wall than their is of shoulder, such the net force working to bulge the case wall outward is greater than that working to press the shoulder forward. You’re also talking about a very different mechanical strength - it’s easy to bulge the belly of a (relatively) long cylinder, while it’s hard to push a short shoulder wall forward. Bend a long rod versus a short one - which is harder? Straighten a sharply bent rod and rebend the corner in a new, close location - is that easier than slightly flexing a long rod? When our internal pressure is sufficiently low to NOT overcome all of the yield limits of the different areas of the case, then the mechanical design and the net forces have different responses from different parts of the case.

Doesn’t happen in standard pressure loads. Happens a lot when guys are trying to cook up safe CoW fireforming loads. Bodies move out, cases get shorter, and shoulders don’t move forward when you don’t have enough internal pressure.

I’ve always considered the FP crush fitting thing to be a red herring. Mechanically, it doesn’t suit that a firing pin would deform a large area (shoulder surface) instead of a small area (FP dimple in the primer cup).

 

[fguffey]

2) Max internal pressure is sufficient to blow the case walls outward, but not sufficient to hold the shoulder forward

Maximum internal pressure is not selective in my cases when chambered in my rifles. Pressure in my cases is equal in all directions. It is nothing personal, it is not even a policy; when pressure builds in my cases and the pressure is described as maximum the case body is forced out to fit the chamber.

This should not be an unknow fact but the pressure can not reach maximum until the case fills the chamber; there is no way the shoulder of the case can be moved back while pressure is building. There is no way the shoulder can move forward if the case body is locked to the chamber and then we have incipient case head separation.

If the case is shoved forward with the shoulder of the case against the shoulder of the chamber and the case body is locked to the chamber the case has no choice but to stretch between the case head and case body. Again: If there was any truth to the powder of the firing pin shortening the case between the shoulder and case head there is no way a reloader can prevent case head separation or the beginning of case head separation.

F. Guffey

 

[fguffey]

And I understand: You believe the shoulder moves, when I fire a case the case forms to the chamber. When the case forms to the chamber part of the shoulder becomes part of the case body and part of the neck becomes part of the shoulder. The shoulder I finish with is not the same shoulder I started with.

I understand you are tired of reading this: I have fired 8mm57 ammo in my 8mm06 chambers; most believe that should result in a catamorphic failure because according to most the case will not stretch .127". After firing I eject 8mm06 cases with very short necks and none of the shoulders moved.

F. Guffey