Excessive case neck expansion on firing.

[morcey2]

This has to do with the rifle mentioned in this thread:

http://www.thehighroad.org/showthread.php?t=730315

It's a Dominican Republic mauser with the original 7x57 21" barrel. It seems that it has a very tight chamber headspace-wise, but has a very oversized throat/neck clearance. All of the cases in question were from factory Remington 140 grain Core Lokt loads, not reloads of any kind. I fired all 20 of them yesterday and was resizing them today. The first thing I noticed was how difficult the resizing was. So, I mic'd the outside of the necks on the 17 that I hadn't resized yet and they all measured at 0.329" to 0.330" outside diameter. I measured a couple that had been fired in my other 7x57, a 1910 Mexican, and hadn't been resized. They measured 0.324"-ish. After I resized the ones fired yesterday, they measured 0.318", but would probably expand slightly with a seated bullet.

Also, I had 3 necks split on resizing, something I've never seen happen on once-fired brass in anything else.

Note: I tried searching to find something on this, but everything keeps coming up with expander dies or neck-turning stuff.

So, is there a spec or rule-of-thumb on when case neck expansion is excessive? The split necks are telling me that I've probably hit that limit on this rifle so it'll probably be rebarrelled, which is what I was planning on when I bought it anyway.

Thought?

Matt

 

[243winxb]

http://www.saami.org/PubResources/CC_Drawings/Rifle/7mm%20Mauser.pdf Looks like .327" is normal for the chamber"s neck. I would worry more about the FL die sizing the necks down more than needed. This is common. Over working the neck may make them split. Then it may be a brass quality problem.

 

[morcey2]

243winxb, I'm assuming you're getting the 0.327" value from the 0.3253" measurement at the neck/shoulder intersection in the chamber drawing, + 0.002" tolerance listed for diameters. If that's the case, I was measuring right behind the case mouth where it should be closer to 0.323" max. (I don't have that doc open, but I've been comparing measurements to the 7x57 in the big-ole-honkin' SAAMI rifle doc. 206.pdf.)

I understand the concern with FL resizing, but I just neck-sized the first case with a Lee collet die and it wouldn't chamber, even thought the case was about 0.001" _shorter_ after firing than it was before as measured with a hornady case length gauge. It's almost like this has a slightly oddball chamber. Maybe I'll just have it reamed out to 280 AI. Ok, not with a 21" barrel.

Matt

 

[243winxb]

The sized .318" neck diameter from the Collet die when compared to the fired .330" plus maybe .002" spring back is about .014" Thats more working of the brass than i would like to see. Hows the accuracy? I loaded an 8mm with a large neck. Light IMR 4895 loads would not expand the neck. Accuracy was ok. Hotter loads that expanded the necks fully, were not accurate. New barrels are nice.

 

[morcey2]

The sized .318" neck diameter from the Collet die when compared to the fired .330" plus maybe .002" spring back is about .014" Thats more working of the brass than i would like to see. Hows the accuracy? I loaded an 8mm with a large neck. Light IMR 4895 loads would not expand the neck. Accuracy was ok. Hotter loads that expanded the necks fully, were not accurate. New barrels are nice.

Here's the best group I got out of it yesterday:

Average groups are somewhat larger than that, but still really good. The 2 holes on the right are from poor fundamentals on my part and were the first two shots.
It'll stay 7x57, but get a couple more inches on the barrel and a new stock. The quandary I'm having is that I haven't had good luck with light or near-minimum loads on anything and I don't want to feed it factory ammo since that's too expensive and very limiting in terms of options.

Matt

 

[fguffey]

Morcey2, thinking about reaming the 7mm57 to 280 Remington? I have friends that did that, seems they did not put enough planning into the ideal, The 280 Remington reamer will not clean up the 7mm57 chamber, the neck on the 7mm57 chamber is larger in diameter than the neck of the 280 Remington. After reaming the neck will have two diameters.

More planning, set the barrel back or tighten the neck on the 7mm57 cases.

F. Guffey