0.03" growth after first fire (264WM WW Brass)

[entoptics]

Fired the first test loads yesterday for my 264WM build (X-caliber bbl). I measured the first case at the shoulder, compared it to an unfired piece of brass, and nearly had a heart attack! Unfired at 2.102", first firing at 2.132"...

Was ready to fire off a raging email to X-caliber (had another issue with this barrel's tenon threads, so I was primed). I took a breath though, and did some trouble shooting...

1) Measured some fire-formed 7mm Rem Mag (multiple firings) from another X-Caliber barrel = 2.132. Identical to the new 264WM within my calipers capability...

2) SAAMI lists the shoulder datum at 2.116. with a 0.42" datum, so my 0.41 Hornady comparator would be a bit longer. Doing the geometry, a 41 should put that closer to 2.127", so my 2.132" is just about right, and on the short end of normal I'd say (Savage barrel nut, so I set it at Go-Gauge plus scotch tape).

3) Remeasured quite a few virgin brass. All at 2.102"

Soooo...My virgin WW brass is just about 0.025" shorter than SAAMI?!?!?

This is some ancient stuff, purchased at an auction by my mom's boyfriend 20 years ago (who knows when it was manufactured before that), so not necessarily a current problem with Winchester. Anyone have any virgin brass they could measure?

I checked for an incipient separation with my RCBS case master, and there's just the barest hint of thinning, so it appears I'm actually OK. I check my 7RM and 300WM brass pretty regularly, and wouldn't think twice if they were showing this tiny level of thinning.

Still kinda amazing. Taking that "Belted Mag Reliability" and lots of headspace thing to the extreme IMO. Somebody around here posted pictures of brass from on old rimmed battle rifle (303 Enfield maybe), and that's kinda how I'm feeling right now...

Almost makes me think I should be getting some Cream of Wheat, then run them through my 277 mandrel, then resize with a false shoulder...

 

[lancetkenyon]

I find new production virgin 7RM & .300WM are consistently. 018"-.023" short on headspace too.
My 7RM, with .420 Comparator, are virgin 2.104", fired 2.124", bump to 2.122".

 

[XSIVSPD]

I've had it happen with my 7mag and 375h&h since they headspace off the belt. I just bump the shoulder for the reloads.

264wm would be the same I would think

 

[Mram10us]

You guys are seeing .020"+ difference and no case head separations?

 

[XSIVSPD]

I don't remember off hand what the measurements were, but it is easily visible when looking at them after firing

 

[entoptics]

I'm used to about 0.010" on most things, and I've seen near 0.020" here and there. Just thought 30 thousandths on a somewhat short chamber was astonishing for virgin brass. Apparently not all that bad? OAL grew by 0.010".

Thanks for the data points.

I of course will minimally size the once fired going forward, so as long as there's no 1st firing incipient separations, I won't get too worked up. That's easy enough to monitor, and I'm used to the chore with my 7 and 300.

I learned the hard way on my first 300WM bbl. Got a bunch of once fired Federal mil surp to start out. Some military load that was so hot, about 1 in 20 had loose pockets. Then I fed them an extremely salty diet of H1000/Retumbo and 208 AMAX. Then I followed the die instructions (Tight plus an 1/8th sorta thing).

Then they started coming out of the chamber in two pieces....

 

[XSIVSPD]

@entoptics some of the military sniper rifles had a special chamber and were loaded way over saami spec. Sounds like you got some of those lol.

On my 375 and 7 it not only moves the shoulder forward, but blows it out to a larger diameter too

 

[nmbarta]

It's because they headspace off the belt, belted mags grow a lot at the shoulder in the first couple firings.
once they are fully fire formed, you can headspace your reloaded rounds off the shoulder just like anything else.
You don't get case head separation because the round is still properly head spaced, so you don't get the typical stretch at the web that you get if you actually have excessive head space. This would be a real issue on a non belted round. It was all done on purpose.

 

[Tiny Tim]

I've never seen that much, but years ago, a lot of my 7 RM brass would show what looked like a ring right above the head after the first firing. This was with factory ammo from multiple manufacturers. Cut a few open because the reloading manuals suggested this was a dangerous condition. Found no issues and after reloading multiple times, it never got worse and eventually disappeared from cleaning. Its always worth investigating.

 

[Mram10us]

It's because they headspace off the belt, belted mags grow a lot at the shoulder in the first couple firings.
once they are fully fire formed, you can headspace your reloaded rounds off the shoulder just like anything else.
You don't get case head separation because the round is still properly head spaced, so you don't get the typical stretch at the web that you get if you actually have excessive head space. This would be a real issue on a non belted round. It was all done on purpose.

I had a second 30 stw built by someone 15 years ago that had case head separations all the time. What do you think caused it?

 

[Dosh]

Manufacturers produce brass to generically fit almost any chamber.

 

[RT2506]

Yes what DOSH just said.
I once had a Rem. 700 in 7 Rem. mag that with new cases no matter the powder or bullet it shot all over the place while head spacing off the belt. With a previously fired case just part sizing it in a FL die, bump the shoulder and size the neck, it would shoot bug holes. You could just about fill the case with Accurate 3100 and cram a 160 gr down to a 120 gr bullet on top and it shot like a bench rest rifle.

I have a custom built 264 Win mag and the chamber is TIGHT. You basically are just neck sizing and bumping the shoulder while full length sizing. It takes less powder to get the same velocity as most data says is max loads even taking into count the difference between 24 or 26" barrels when mine has a 27 3/4" barrel. I just subtract 25 fps off my barrel length down to theirs. 130 gr Accubonds at 3350 fps is like a laser beam shooting across a bean field at deer. You almost hear the bullet pop before you realize the gun went off. LOL

 

[J E Custom]

Belted Magnums are designed to have excessive head space for chambering in any chamber conditions. they were also designed for safety (Not the reloader) when pressures were not as high as they are today. If you reload new brass I recommend loading a standard or starting load to fire form the new cases. You can still hunt with them but at the same time get a good fire form that doesn't over work the new brass.

Some brands of brass are harder than others so it is normally best to use starting loads for this reason. Once they are fired it is best to size only enough to chamber because if you full length size a belted case you will experience the same problem because you returned it to SAMMI spec.

If you do a minimum sizing on a belted case it will no longer head space on the belt and rely on the shoulder for than critical dimension. The shoulder will control the case stretch to a minimum if this is done. you can do a neck size only an reduce it more, but some like the minimum sizing method and it can be used the same way for the same reason.

J E CUSTOM

 

[nmbarta]

I had a second 30 stw built by someone 15 years ago that had case head separations all the time. What do you think caused it?

It's hard to say for sure, but from what I've seen, when someone is having case head separation with belted mags and reloaded ammo, they are usually over sizing the brass. Over sizing any brass can cause early case head separation, but in the case of belted mags, this problem is much worse. JE explains this pretty well, though I would argue that they don't really have "excessive head space" as they are head spaced off the belt, this is just a terminology thing. They have excessive "slop" in the chamber. Belted mags can still be improperly head spaced. Excessive head space would imply that the reamer was run into the chamber to deep causing the head space off the belt to be incorrect.