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

[cajun]

I dont think you can get accurate actual headspace measurements with a comparator. It's just a reference to compare one to the other. As other's have said it's common to have a lot of movement on the first firing with belted mags. I normally see 10-15 so thirty is an awful lot. If your confident in your chamber the brass may well be under spec. The key is only bump the shoulder minimally from here forward. I had a set of lee dies in 350 Rem mag that would bumb the shoulder .014 if you followed the die instructions. Needless to say that is a recipe for a case head separation and why I started using a headspace comparator.

 

[Mram10us]

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!

I am slow so not seeing where the .0258 and .0091 are coming from. I'll study up more. Just when i thought i understood saami prints.....

 

[Mram10us]

@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.

Math looks good for .041 datum and appreciate you posting all this. I had no idea they sold brass that short, especially when outside of saami spec. I measure my brass(to datum) now but never did when I was starting out.

 

[Travler]

thank you all for the reloading info and the start to my education on brass and the specs , any one have a good recipe for the 264 WM 100 grain bullet light on recoil

 

[ThrdKllr]

I form my 7mmRM brass from 300 WM to prevent there being any stretching and then only push the shoulder back.002-3 to headspace off of the shoulder. It takes a good bit of work to do but I end up with good long lasting brass without the chance of a head separation. Have to turn the necks after they are formed.
Just got a new 300 and have the new Peterson long brass ordered to see how that works.
Don't know how that's going to work though by not resizing all the way down to the belt to keep from pushing the shoulder back too far. May have to cut a f/l die off below the shoulder to size the case further in front of the belt?

 

[rsnell]

You must remember the Hornady case comparator is only a comparator and can not be compared to SAAMI specs or anyone else's measurement. Refer to the J E Custom reply to understand what is going on and how to deal with it.

 

[Mike Matteson]

I differ a little on case base separation does occur in belted magnums. (If I read the above correctly) I fire form all my cases. I shot a 308 Norma Magnum in Mauser 98 action, 26" barrel. Purchasing cases is almost impossible or very expenses to get. It is correct that headspacing is off the belt. Being my case is shorter at the shoulder than a 300 WM. The neck is longer on my 308NM than the 300WM. I use a 300 W.Mag neck sizing die after completing fire forming my case. That only sizes the neck about have way. Leaving the balance of the neck at chamber size. I found by mistake in the early 2000 that is help my grouping. I use 165gr Nosler AccuBond or ballistic tip in that rifle. My velocity is 3300+fps with H4350, Fed 210 primer, and Winchester brass, from that rifle. I do weigh the brass, and turn my necks after fire forming my brass.

 

[ThrdKllr]

You must remember the Hornady case comparator is only a comparator and can not be compared to SAAMI specs or anyone else's measurement. Refer to the J E Custom reply to understand what is going on and how to deal with it.

Exactly. And that's why I didn't list any specific numbers. I use it to compare fired brass to new unfired brass. I'm not going off of any chamber or reamer print.
I also have to turn the necks on the brass reformed from longer brass since the shoulder becomes part of the neck.

 

[Far North Hunter]

I appreciate the comment about setting a false shoulder for fireforming. Has anyone upsized 7mm virgin brass to .30 then neck sizing down with 7mm to create the false shoulder..lots of work and annealing. Not advising, just curious.

 

[ThrdKllr]

Not necessary because case headspaces on the belt and not the shoulder.

 

[Send it 284]

And this thread illustrates why belted cases suck.
I got rid of all mine after dealing with case head separation in 3 firings

 

[entoptics]

Not necessary because case headspaces on the belt and not the shoulder.

That's not quite correct, If you're referring to "false shoulder, jamming, etc" fire forming methods, mentioned by @Far North Hunter, and perhaps others.

As @bigngreen mentioned I believe, that belt has headspace tolerances. In a tight rifle it's probably ≤0.004" between the bolt face and chamber face, but there's up to 0.008 less allowed on the brass specs, so let's call it 0.01" total.

Jamming or a false neck will mitigate a good chunk of that rearward travel, which would be taken up by thinning of the case head, just in front of the belt. Is it worth the trouble to fire form at all (juss shewt em!)? I'm modeling and measuring that currently. I'll report my findings as they come in.

 

[West Calamus]

Maybe a little off topic. Don't have a comparator or fancy die set-ups. What is the best way to set belted case resizing die? Here is what I do so tell me if I shouldn't be doing this. Hornaday custom grade dies - case once fired and annealed, run shell holder up until it contacts die at top of stroke then back die off 1/4 turn and size case. Cycle in rifle, if bolt will not lock then slightly screw down die until bolt locks with slight resistance on bottom third of of lock stroke. Sig brass with about 7 firings with a few hot loads during testing and not aware of any signs of case separation.

 

[Stammster]

You must remember the Hornady case comparator is only a comparator and can not be compared to SAAMI specs or anyone else's measurement. Refer to the J E Custom reply to understand what is going on and how to deal with it.

True. But if you have any gauges (go, no-go, etc.), you can measure them with your Hornady comparitor and determine the offset.

When you measure your fired brass, apply the offset. Voila - now you can properly compare to SAAMI.