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

[bigngreen]

This is normal unless custom spec'ing a reamer then the need for custom dies as well, the shoulder to base is not headspace in a belted mag UNTIL the shoulder blows out farther than the headspace on the belt then the reloader either headspaces of the shoulder or the belt based on the sizing. I typically fire my first round on belted mags with a bullet jambed so the brass is taken from the shoulder when blowing it out not the base then you're good to go with shoulder head spacing.

 

[Mram10us]

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.

I understand that. The point i am getting at is, if you get a case head separation due to oversizing the brass (pushing the shoulder back to far), you should get it when firing brass that is .030" short. The only remedy is false shoulder or jamming a bullet like BG referenced. I have not seen any belted mag cases even .020" short of saami, but maybe I'm lucky. That is why I questioned his headspace.

 

[XSIVSPD]

One thing to keep in mind is that most cartridges headspace off a datum point somewhat centered on the angled portion of the shoulder. If the virgin brass has a shallower angle it may still headspace properly (even at the shoulder since we're talking about cartridges that headspace off the belt), but it will be moving the shoulder forward.

At that point its doing basically the same thing that an AI chamber would do, just less extreme. Many people measure for headspace issues by measuring to the start of the shoulder since the datum point is hard to measure to without specialized gear. If that's what the OP is doing then it could easily show 0.030" worth of movement with changing the actual headspace much at all

 

[bigngreen]

I understand that. The point i am getting at is, if you get a case head separation due to oversizing the brass (pushing the shoulder back to far), you should get it when firing brass that is .030" short. The only remedy is false shoulder or jamming a bullet like BG referenced. I have not seen any belted mag cases even .020" short of saami, but maybe I'm lucky. That is why I questioned his headspace.

Most if not all of the case head separations I've seen have been a cumulative effect of the brass being pulled at the base when blown forward the pushed up into the neck when resized. How fast that separation happens depends on how much it moves each time and the thickness and harness of the case. It's also more pronounced with non belted cases because they push all the way forward case expands and grabs the walls then blows back so ALL of it comes out of the back with a belted mag being held back by the belt there is stretch across more of the case since it's all blowing forward.

 

[Bob Wright]

My 7RM brass grew .019 after a second reload/anneal. It's normal and part of the parent case design so many years ago. It was a dangerous game load, and "guaranteed" to chamber as that elephant was stomping on you, lol.

 

[Mram10us]

This problem is driving me crazy. Why is brass being sold that is .010"+ less than even saami mins? Saami already gives .009"-.010" for the belted mags I looked up. Frustrating that so many are seeing huge gaps from virgin brass to chamber mins.

 

[eschafer]

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.

This here above, explains it perfectly... I only wish I heard it explained this way when I started to reload.... The arguments online about Belted Magnums and Headspace can be confusing and incomplete.....

Because the case is headspaced on the belt for the first firing, there isn't much space for the case to stretch backward toward the bolt... The bolt stops excessive stretch. (This assumes your chamber is head-spaced correctly).... Rather, the case gets FORMED forward in the chamber shoulder area with minimal stretch... The stretch is minimal because the case is free to FORM with little to stop it.... You'll see a little loss of neck length lost to the FORMING action.....

I have two 50 piece bags of virgin Belted Mag (.338 Win Mag) brass yet to be reloaded... Winchester and Hornady... 0.022"and 0.016" short from base to shoulder compared to my chamber, respectively.... For the longest time I was reluctant to reload them for fear of case head separation... I've since realized that these virgin cases are no different than the brass from factory rounds that I've been reloading to date, and presently at 5 reloads... Soon I'll take the plunge without anymore fear and reload the Winchester and or Hornady cases... I'll just continue to set my sizing die to only bump the shoulder 0.001"- 0.002"" short of my fired cases.....

 

[bigngreen]

This problem is driving me crazy. Why is brass being sold that is .010"+ less than even saami mins? Saami already gives .009"-.010" for the belted mags I looked up. Frustrating that so many are seeing huge gaps from virgin brass to chamber mins.

Look at the saami specs for the chamber then the brass and you'll find your answer, your right on the head spacing which is the belt but the tolerances for the shoulder are very wide.

 

[ATH]

Doesn't help for your rifle, but at least one brass maker has addressed this issue. I believe it's Peterson that sells "300WM Long" brass which comes ready to headspace off the shoulder.

 

[Mram10us]

Look at the saami specs for the chamber then the brass and you'll find your answer, your right on the head spacing which is the belt but the tolerances for the shoulder are very wide.

I looked them up which is why I dont understand why they are that far off. OPs brass was .015"+ less than saami mins. I highlighted the values.

 

[Bob Wright]

This here above, explains it perfectly... I only wish I heard it explained this way when I started to reload.... The arguments online about Belted Magnums and Headspace can be confusing and incomplete.....

Because the case is headspaced on the belt for the first firing, there isn't much space for the case to stretch backward toward the bolt... The bolt stops excessive stretch. (This assumes your chamber is head-spaced correctly).... Rather, the case gets FORMED forward in the chamber shoulder area with minimal stretch... The stretch is minimal because the case is free to FORM with little to stop it.... You'll see a little loss of neck length lost to the FORMING action.....

I have two 50 piece bags of virgin Belted Mag (.338 Win Mag) brass yet to be reloaded... Winchester and Hornady... 0.022"and 0.016" short from base to shoulder compared to my chamber, respectively.... For the longest time I was reluctant to reload them for fear of case head separation... I've since realized that these virgin cases are no different than the brass from factory rounds that I've been reloading to date, and presently at 5 reloads... Soon I'll take the plunge without anymore fear and reload the Winchester and or Hornady cases... I'll just continue to set my sizing die to only bump the shoulder 0.001"- 0.002"" short of my fired cases.....

You got it. It's standard to have that shoulder gap significantly different than a non belted cartridge. My new 280AI brass was only. 002 shorter than my chamber when brand new. Apples and oranges...
Glad for your understanding. I did get uniform shoulders on the mag belted case after an anneal and second firing. At that point they still varied up to .004 but annealing was the trick. Now I just bump .002 and will accept .003 if needed, but rare.

 

[bigngreen]

I looked them up which is why I dont understand why they are that far off. OPs brass was .015"+ less than saami mins. I highlighted the values.
View attachment 232041

Ok, hopefully I get this right as I'm switching screens on my phone.
If your take your specs and figure min brass and max chamber you should be at .0258 max clearance to .0091 min clearance for the shoulder datum spec. and belted mags tend to be on the longer side of spec traditionally for clearance there. The OP 2.132 number is .003 inside max spec.
If I haven't jumbled a number!

 

[bigngreen]

With a belted mag you can then complicate it farther by looking at Max belt headspace vs Min belt on the brass which gives you a possibility of .015 to .000 of belt head space clearance WHILE remaining in spec which will move the shoulder spec as well. LOTS of play in a belted mag!!!

 

[entoptics]

@bigngreen and @Mram10us Just to assist and clarify with the math that's being done above...

I'm measuring the virgin brass at 2.102 to shoulder. That's 0.014" below datum (2.1162), and 0.007" below minimum tolerance. AND THAT'S WITH A 0.41 BUSHING IN MY COMPARATOR! On a 25° shoulder, that extra 0.01 means my measurement should be ~0.01" longer than the SAAMI diagram would say.

So these bad boys are short. Like 0.017" short of shortest allowed...

Also, this is a Savage pre-fit. I set headspace at Go-Gauge plus a smidgen. Painter's tape (≤ 0.004") on Go-Gauge was a HARD (as in not a chance), No-Go. Measuring fired brass, I'm getting 2.132". Subtract the 0.01 for the 41 bushing, and that's 2.122", which is actually a smidge BELOW minimum SAAMI spec.

Add that all up, and my WAY below SAAMI spec brass are growing 0.03" on first firing in a below SAAMI minimum chamber. In a max SAAMI chamber, that would be 0.04" growth.

@Mram10us I'm not alone in your surprise. Hence the thread.

That said, I have the tools to monitor incipient separation, and at least the first round of test-load brass, appears to be just fine.

I think I'm going to do an experiment next on 12 each of virgin, neck turned virgin, and once fired.

1) Pin tumble
2) Measure case volume and dimensions
3) Run two powders and two bullets, 3 shots per recipe.

It's 3X the supplies, and I hate to waste bullets (primers?) during these times, but I'd rather figure out the consequences of my actions and new equipment, sooner rather than later.