HELP! Short stroking?

[chunger]

So I finally got my 2 California rifles together, and got out to the range to sight in and function test/break in.

I find one of the rifles (multicam one) does not lock the bolt back on empty mag. . . well, it does once out of every mabe 30 or so opportunities.

The pink rifle runs very well. Everything about the 2 rifles rear of the barrel is identical except for the color. I swapped out the bolt carrier groups, and the pink rifle still runs like a top, and the multicam one still fails to lock back.

It also induces a bad jam w/ some regularity. Round fails to strip completely and the bolt does not go into battery. Upon forceable removal of the mag, the partially stripped round has a huge dent across the top of the casing. I chuck the round.

I have all of tomorrow to try and sort this rifle out, but I work all Wednesday and go to shooting school w/ the wife on Thursday. . . so I'm freaking out a bit because I don't know how to further diagnose the problem or if there is anyone in the Bay Area I can take this to on such short notice.

Is it the gas system? Should I try a lighter buffer spring? Is it even possible to adjust the gas system at home?

[C.G.]

Sounds like a mag problem. They are not ProMags by any chance?
Without seeing the mags I would check the feedlips, deburr any burrs and "exercise" the mags with a stick a few times.
BTW, what kind of ammo were you using?

[chunger]

New C-products 10 round mags w/ Magpul Gen II followers. Feed lips have been de-burred prior to any firing. Exhibited same problem with PMC 55 grain FMJ and Winchester white box 55 grain FMJ

[C.G.]

New C-products 10 round mags w/ Magpul Gen II followers. Feed lips have been de-burred prior to any firing. Exhibited same problem with PMC 55 grain FMJ and Winchester white box 55 grain FMJ

Eventhough C products are supposed to be good, there were some instances of problems. It still sounds like a mag problem, try different mags.

[ar15barrels]

I forgot to mention on the phone that you should lube these heavily for the first few hundred rounds.
If these are brand new builds, you need to fully break-in the gas rings, carrier and receiver before you can expect perfect function.

If you have a couple hundred rounds through the gun and it was kept really wet, THEN I would recommend opening up the gas port a tad.

Any chance that the INSIDE of the receivers got painted?
That will cause problems too.

The paint on the barrel is going to make FSB removal a problem.
Expect to have to re-paint that after it's put back together.

[chunger]

Thanks for the call Randall,

There's no paint on the inside of those upper receivers. . . except on the back of the dust cover. I completely masked them prior to painting because my understanding is that the factory teflon coating is excellent for internal parts.

There are presently ~120 rounds through the rifle. . . and I've been running it wet with FP-10. I've not seen any improvement yet through the course of break in. Many of the shots have been 1 or 2 rounds loaded to check for slide lock-back.

[RobG]

Not sure what upper you are running but, I have a Stag that did the same thing. Sent it back and they resolved the issue promptly and paid for shipping both ways. They opened the gas port and replaced the bcg and now it is flawless. They apparently had a bad batch that caused the issues.

[m24armorer]

Paint on the barrel is no problem. Just drive the pins out and rotate the sight 180 deg. Now gee, there is a perfect hole right there where the sling swivel was and there is the gas port.

[ar15barrels]

Paint on the barrel is no problem. Just drive the pins out and rotate the sight 180 deg. Now gee, there is a perfect hole right there where the sling swivel was and there is the gas port.

That's what I'm planning to do.
Sometimes it's fun to get the gas tube out with the FSB painted into place though.

[m24armorer]

At least you can't see where the hole gets EDM'd when you rotate it back.

[ar15barrels]

At least you can't see where the hole gets EDM'd when you rotate it back.

Who said anything about EDM'ing it?

You EDM your gas ports?

[m24armorer]

Every dang one.......

[ar15barrels]

Every dang one.......

Nice.

I wish I had an EDM.
That's proably one of those things that I would use all the time if I had it.

I got along for years without a surface grinder.
Now that I have one, I use it all the time.
I can't imagine NOT having a surface grinder now.

[m24armorer]

Kinda funny how we wound up with it. I bought a Sargon DRO for a lathe off Egay. It was a local company so I drove over to pick it up, when I was there I asked if they had anything else that they wanted to get rid of.

In the corner of the shop was a brand new $65K sinker EDM. It was purchased by the former owner and never used.

Cost me a hundred bucks plus trailer rental.

You should be able to find one in SoCal easy. Check Ebay.

[m24armorer]

Cleanest burr free ports you ever saw....