Problem?

[nmxdaven]

Hey all,

First off is the obligatory picture of my new build.



Running a Satern 24" with the brownells supplied bolt.

I ran some wolf through it to set the gas block and get everything smoothed out. After that I ordered in 600 rounds of hornady 123 to start getting some brass stocked.

Initial impressions were great. A pic of 3 shot groups at 150 yards.





I ran 40 rounds of factory amax through it at first. Brass looked fine.

On my second outing I ran 50 rounds. At first, the brass looked perfectly fine as shown.



But then, after 10-15 rounds, the brass started to develop a bright ring. Almost looks like a case head separation issue.



Can't feel anything with a paper clip. Primer looks perfectly normal. No other signs of strangeness, just the ring with a slight raise to it.

Any ideas?

[Rickc]

This is all factory ammo no reloads correct?

Check headspace with your go/no go gauge

You need to use a Hornady headspace gauge. Check fired and unfIred brass and see how much it expanded when fired. Compare that to sammi specs.

You may have a headspace problem. Could be you set it up long when you installed your barrel or you have a long.chamber.

If all that checks out then you have.a bright ring on your brass. Might be an imperfection in the chamber that causes no real problem.

[nmxdaven]

All factory ammo.

I have a few brass that I failed to toss through the wet tumbler on my first outing that do not show the ring. Again, the first 40-50 rounds look perfectly normal.

"Normal fired case": 1.514
Ringed Brass: 1.517
Ringed Brass: 1.517
Raw Brass: 1.511

I guess my next step is to check head space. I don't have a 6.5 gauge, I used a buddy's when I set up the rifle. Will have to meet up with him again or order one in.

[Rickc]

Question is.why the increase in expansion from .003 to .006.

Still not bad. .005 is very common. I shoot for .003 with my reloads

[nmxdaven]

That's what is bugging me.

Just checked through my brass bin. Those numbers are decently consistent through all of the "good" fired brass vs the "banded" fired brass.

Ammunition is all from the same lot. Rifle wasn't even cleaned in between.

[204 AR]

Maybe dirty chamber? Cases gripping the walls a little better than if it was clean and being stretched that little bit more? Grasping here.

[LRRPF52]

It's normal. A likely cause is that your gas system has fouled in the areas that leak in the first firings for a while, then seal up, making it a more closed and efficient gas circuit.

This increases carrier velocity, which will show up sometimes as cases still trying to de-obturate during extraction.

I just looked at all my cases from yesterday's range session, and they have the same condition.

I'm going to process them like normal, set my shoulders back .003-.005" and walls down as well of course, and not look back.

You can fight it with carrier weight or adjustable gas.

[nmxdaven]

Interesting! I will play with turning the gas block down a bit on my next session and see if that clears up the brass. Thanks for the help.

Also I managed to get the 6.5 go and no go gauges today and everything looks like it checks out.

[LRRPF52]

It's not as pronounced in the picture, but they look very similar to yours. This is Lapua brass, 123gr SST, 31.2gr CFE223, Rem 7 1/2 primer, 2.245" COL.

I just shot them from my 16" AA MLGS Monday.

[nmxdaven]

Very similar. Has it done that for long? No problem with brass life?