Help with headspace

[BERGA]

I just installed a Lilja AR1024 barrel on my AR10T in .260
I wanted a threaded muzzle and a gas block journal of .936" as there are not many choices for the .875" Armalite gas block.
Lilja says on his web page that his barrel will headspace with all known bolts Except the KAC bolt.
Iam useing the JP low pro gas block and an Armalite rifle length gas tube, the barrel nut lined up at 50ftlbs so I did'nt go any tighter.
At the range today my brass showed signs of gas leakage with black carbon leaking past the shoulder and down the side of the case. My velocity was jumping all over the place with spreads of 100 fps or more.
This leads me to beleive I have a head space problem.
What should I do next ?
I tried cleaning the chamber real good and then turned the gas
off fired a round and the brass was clean when I ejected it.
Any advice would be appreciated.
KB

 

[country888]

Re: Help with headspace

If case was clean with gas off, it may not be a head space problem. May be cycling to fast, bolt unlocking early. Try a heavier buffer or if you have an adjustable block turn down the gas.

 

[BERGA]

Re: Help with headspace

That is what I thought, that is why I tried it with the gas turned off. Is there any difference in a DPMS barrel extension and the armalite ? I noticed that the bullet tips are deformed from smashing into the barrel shank at too steep of an angle and after chambering a round,even with a crimp, the COL is .020 shorter. Iam thinking that the velocity changes are from seating depth changes. So I might SOL if my AR10T uses the old style mags and the DPMS extension needs a Pmag style.

 

[338Federal]

Re: Help with headspace

I noticed you said you used an Armalite rifle length gas tube with a DPMS format barrel/extension. It has always been my understanding that Armalite made there gas tubes to a slightly longer spec and are only to be used with there barrels.

There is a difference in the extension as well, both use different specs. In other words an Armalite extension will not headspace with a DPMS bolt and vice verse. Its sounds like you put a DPMS barrel in an existing Armalite setup, and this does not work in the large frame AR's.

 

[Bennybone]

Re: Help with headspace

Dude why two threads at once?

Pick a thread, any thread