Gunsmithing Question about proper head spacing....

[BigtimeAub]

I have a REM700 BDL rechambered in .308, up from .270. I've probably shot close to 400 rounds since I picked up the rifle from the gunsmith. I don't know a lot of the technical details that I should probably know but was hoping that someone could help me figure out what is going on. I've been shooting three different loads, only the brass changes while all other components stay the same. The three different types of brass are Lapua, Winchester, and LC (once fired, remanufactured military brass). The load is 175smk, 42.8gr Varget, Federal 210 primers, 2.810" OAL. The problem that I'm experiencing is with the LC brass, I'm having what I think is called "case-head separation." Am I correct on that? I've never had any other problems with other brass, just the LC. Is there a difference in the size of the case head that would cause this, or would it be more likely that there is a discrepancy within the case wall/webbing that would cause this issue, since the Lapua and Winchester brass isn't having any problems. I'm still very knew to all of this so I would greatly appreciate any explanations/advice/thoughts that I could get. TIA

EDIT: These seven cases are out of close to two hundred rounds loaded in LC, as in 7 rounds out of a case of 200.

The two cases on the far left and the one case on the far right are also ruptured, but only slightly. No gas or carbon seems to have come through those casings but there is what seems to be a surface crack on the outside case walls.

 

[42769vette]

Re: Question about proper head spacing....

somone will be along shortly that knows alot more than me. i believe that lc brass is thinker, leaving less combustion space inside the brass, meaning higher pressure.

 

[wnroscoe]

Re: Question about proper head spacing....

How many firnigs per case?

Looks to me like your FL die is pushing the shoulder back too far each time you FL size.

The FL die should only be bumping the shoulder as to only push it back .0015" to .002" max

 

[BigtimeAub]

Re: Question about proper head spacing....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: 42769vette</div><div class="ubbcode-body">somone will be along shortly that knows alot more than me. i believe that lc brass is thinker, leaving less combustion space inside the brass, meaning higher pressure. </div></div>I probably should've mentioned this in my OP, but with the Win/Lapua brass, I've hand loaded those and my loads are at 44.2gr of Varget with absolutely no pressure signs and pressure signs starting show only once I worked up to 45+gr. So, would you think that the LC brass is thicker causing internal volume to be lower than the Win/Lapua brass so much so that the pressure is that much greater than the 44.2gr with only 42.8? Also, there aren't any extraction marks on the case heads, just the separation. (My ADHD is getting the best of me tonight. Probably should've mentioned that last part in the OP as well.) But thanks for the reply.

 

[BigtimeAub]

Re: Question about proper head spacing....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">How many firnigs per case?

Looks to me like your FL die is pushing the shoulder back too far each time you FL size.

The FL die should only be bumping the shoulder as to only push it back .0015" to .002" max </div></div>The LC brass came loaded. I guess you would call it factory ammo, but not really. The brass "should" only have been fired once before.

If it is an issue of the shoulder being bumped back a little too far, how could I measure this properly (considering I don't have the necessary tools/gauges)? TIA

 

[wnroscoe]

Re: Question about proper head spacing....

Is this ammo new to you reloads or factory new ammo?

 

[BigtimeAub]

Re: Question about proper head spacing....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: wnroscoe</div><div class="ubbcode-body">Is this ammo new to you reloads or factory new ammo? </div></div>The brass (LC) is once fired, then reloaded and sold to the public. All other brass (Lapua/Win) was new, never fired.

 

[eddieharren]

Re: Question about proper head spacing....

Who did the re-chamber work? If the gunsmith is local, he could make you a case length gage with the reamer he used for your chamber. I make them for all of my customers who reload. When used with a set of dial calipers it can show you how much you are relocating the shoulder. If it were my choice, I would not shoot anymore of the LC ammo in my rifle.

 

[BigtimeAub]

Re: Question about proper head spacing....

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DocEd</div><div class="ubbcode-body">Who did the re-chamber work? If the gunsmith is local, he could make you a case length gage with the reamer he used for your chamber. I make them for all of my customers who reload. When used with a set of dial calipers it can show you how much you are relocating the shoulder. If it were my choice, I would not shoot anymore of the LC ammo in my rifle. </div></div>
Thanks, Doc. He's sort of local, about 4 hours away. I'll give him a call and see what he can do for me. Worst case, I'll just have him fed-ex a gauge to me.

 

[funk]

Re: Question about proper head spacing....

To do a quick check of how much your resizing your brass is take a 40s&w casing put it on the shoulder and measure your fired brass against the full length sized. That will give you the amount that your resizing.

 

[wnroscoe]

Re: Question about proper head spacing....

Once fired then loaded and shot shouldnt seperate like that. Typically, case head seperation is from repeated firing and over sizing.

If Lake City is the only brass seperating I'd say there's a major problem with it and it's trash. The problem with remanufactured ammo is you never really know the condition of the brass prior to it being reloaded.

Rule #1, never, and I mean never, shoot anyone elses reloads from your rifle.

I'd run new brass in the rifle and just bump the shoulder so it fit back in my chamber.

 

[EXTREMEPREJUDICE]

Re: Question about proper head spacing....

Often LC brass has been fired by full auto weapons such as the M-240 machine gun. The chambers of those weapons are oversized to help in the extraction of spent rounds and subsequently the brass stretches quite a bit more than in a bolt gun. Head case separation during subsequent firings is not that unusual as it has to be worked back quite a bit into spec when resizing. That's ONE of the problems that can occur when using brass obtained post military use. Just a possibility.

 

[sinister]

Re: Question about proper head spacing....

It appears you are having incipient case head separations on the remanufactured ammo using Lake City brass.

7.62 fired in a machinegun with excessive headspace may stretch excessively after the first and second firings (as you're experiencing).

Someone got a good deal on surplus machinegun brass, processed it, loaded it, and you thought you got a good deal.

I doubt there's anything wrong with your rifle.