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Discussion Starter · #1 ·
I got some LC 7.62 cases to reload that were prepped when I purchased them. Out of 100-120 rounds that I fired 35 had partial head separations . The initial length was 1.627 The fired length was as long as 1.650 on these cases . They will not rechamber in my rifle. I also fired some of my LC match and some OFV factory loads. These averaged 1.638 to 1.641. These also will not rechamber in my rifle, they will if I push down on the bolt lug with my thumb. How could the cases be so much larger than my chamber is? These were in all likely hood MG fired brass. Is it possible that they went back to the size they were when fired in the MG ? My HS is on the long side at 1.636 but passes the field test gauge.
 

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Need additional info like the cases in question were not prepped by you ? how many reloads were on these cases ?, your chamber is slightly large but I have seen worst, my suggestion would be is to take some ammo of known quality (not reloads) and fire 5-10 with the gas system off and then use a HS gage (Hornady is one) and measure the cases to get an average.

Also what type of load did you use ? what was the OAL/OGL, what type of bullet etc....

In reference to the fired cases, a M14/M1A is one that is not kind on brass, the cases are actually extracted pretty hard so brass life is not long especially if loaded hot like in 3-4 max reloads.
 

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It is typical that a fired case will not chamber until it has been resized. Regardless of whether it was a new case, or a reload.

Your LC72 cases were probably stretched quite a bit on earlier firing, and that weakened the metal - giving your head separation troubles.

I suggest only using 'fired cases' when you really know their complete history.

Jay Kosta
Endwell NY USA
 

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You shouldn’t be getting a case head separation on LC surplus sold through known vendors our sources. If you were using a fairly standard load; within service rifle specs and not trying to push the velocity boundaries, that failure rate on cases would prompt me to throw out the entire batch.

I have never seen that kind of failure rate on cases, even on cheap 50’s era surplus ammo. Whether they were overloaded, bad brass, bad prep, whatever, the surviving cases probably went through the same or close to the same history and you’re probably sitting on even more potential case head separations at the next firing.
 

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Discussion Starter · #5 ·
Load was 168gr Matchkings varget 41grs or 42 in some brass was not prepped by me except the match brass and I had no problems with it. The loads were 3-4 grs below max. The LC that failed was on first reload The match was on its 3 rd or 4th loading.
 

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Probably not your issue.
Last year I had a barrel done by someone who should know better.
It will just barely close on a no-go. Cases come out .016" longer than a no-go gauge. WTF? Turns out that in addition to being too long in the headspace the gas port was oversized and the rifle was way over gassed. It was jerking cases out way early in the pressure curve. Hence the extremely long dimensions.
In this condition brass was only good for one reload.
Replaced with a Krieger hvy and all is well.
 

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This is confusing.

1. The cases are being ripped apart, like the headspace was too large.

2. The cases will not allow the bolt to close, like the headspace was too small.

Can MG cases fired in open bolts, then refurbished and sized to fit in closed small chambers, suddenly spring back to their stretched condition when fired again in small chambers? .... NO!
 

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Discussion Starter · #8 ·
Cases are cracking 1/2 inch up from base at the end of the web just like the pics posted here on the "Incipient case head separation"post. Bolt closed fine on the loaded brass.I dont understand how the brass could be so much larger than the chamber.
 

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The tell-tale bright ring, 1/2 inch up from the head face, is usually the incipient case separation line.

Original case forming operation typically causes that section to be the hardest (least malleable) and the thinnest of any part of the case. If the case is exercised in firing, stretching, and reforming in that area to a significant amount, the material hardness reaches the point where there is a very high stress level in the material causing a brittle fracture all around or case separation.

Often, case seal-to-chamber is not broken and no plasma jets out onto the bolt face. The first sign is only part of the case is ejected and / or the next round telescopes into the remaining body of the separated case.

There are several factors that can cause that area to be highly strained and stressed.
1. A large diameter, or slick or oiled diameter of the chamber, or a residual lubed case.
2. A large residual axial space between the case head surface and closed bolt face.
3. A prepped case with a lost history of being severely stressed or strained in that area.
4. Unlock of bolt before decay of chamber pressure.
5. Multiple cycles of firing and reforming.
6. A combination of the above factors and possibly others not mentioned here.
 

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Without physically inspecting your fired cases it's all a guess. Fired brass not wanting to load back into your gas gun's chamber is the least of your problems. My guess - and that's all - is you got hold of some overworked brass near or due for retirement. You just never know.
 

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It's normal that your fired cases won't chamber without a fight.

It sounds like you've got mixed headstamps, so some is going to grow more than others because some are more work hardened, thicker, etc--just a mixed bag of mechanical properties.
 
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