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Is It Time For a New Barrel Extension?

PostPosted: Wed, 25 Nov 2015 21:32:23
by MarcSpaz
So, I am going to call SIG on Monday to see if I can schedule sending my 516 in for a new barrel and a Gen 2 gas system. Does anyone know if they will automatically replace the barrel extension or must I specify I want it replaced?

The reason I ask, I think it needs to be replaced because of an ammo feed problem. But, I almost think it may possibly be an over pressure problem with the gas system as well. I just don't know how to tell.

So, when I am shooting... at least twice a mag, I get a jam and the bullet comes out looking like this...


I tried new mags, old mags, PMags, and CP GI mags. Doesn't matter what mag, the same problem occurs. Also, I tried both 55 and 62 grain rounds with the same results.

Part of me things it an over pressure problem because it only happens with 5.56mm NATO rounds, not lower pressure .223 Rem rounds.

Then, another part of me says its a wear problem, possibly with the barrel extension, because it has never happen before this past weekend and I have roughly 20,000+ rounds through it.

Any ideas?

Re: Is It Time For a New Barrel Extension?

PostPosted: Fri, 27 Nov 2015 07:50:29
by grumpyMSG
You need to let the folks who work on the rifles do the diagnosing. Send them photos of the rounds. Give them the symptoms. You think the rifle is suffering from an "over pressure" problem. You are incorrect and here is why: Your rifle's gas system only moves the piston and bolt system to the rear and it stops. The buffer spring and the mass of the buffer and the bolt carrier is what returns the bolt forward, strips the next round out of the magazine, feeds it into the chamber and causes the bolt to collapse into the carrier and rotate into the locked position. Those rounds are damaged when they are being shoved forward. If you have been playing with a heavier weight buffer and a stronger buffer spring, you have done the equivalent of swinging a heavier hammer faster while driving nails and it takes 3 strokes to drive a nail instead of 6. If you have done any such modifications to your rifle you need to let the folks working on it know exactly what you have done, to include letting them know whether you are running it with a suppressor and what setting you have been using on the gas regulator.

Without seeing your rifle, I am going to speculate your issue is not the barrel extension at all. I would guess the feed ramps on your upper receiver are worn out. The rounds hit them before they hit the steel of the barrel extension. aluminum being the softer metal, will wear faster than steel. On military rifles it is more easily spotted with blanks because the star shaped crimp catches on the "lip" ,that is exposed as the upper is worn, far easier than a standard ball round.

If you have honestly gotten 20,000 rounds out of a barrel you are a lucky man, it should have been shot out somewhere around the 8-10 K mark. I know I couldn't tell you how many rounds I have through my various rifles' barrels. I would just guess it is a couple of grand through the A1 and A2 barrels and probably around 1000 on my M4gery.

Re: Is It Time For a New Barrel Extension?

PostPosted: Fri, 27 Nov 2015 09:24:01
by MarcSpaz
Thanks for the feedback. The rifle has one mod... the trigger.

I always thought the feed ramps were part of the barrel extension, which is why I mentioned replacing it.

Re: Is It Time For a New Barrel Extension?

PostPosted: Fri, 27 Nov 2015 13:54:00
by Jeff82
Some are, some aren't. If you have "M4 feed ramps" you'll see ramps cut on the upper receiver matching the cuts on the barrel extension.

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