What muzzle device is on the problem rifle?

I put on a Spike's Barking Spider on one of my AR's. It began to have about 4-5% failures to extract. The Spider was causing an increase of gas back pressure causing the bolt to try and open sooner than normal before chamber pressure could go down enough to allow extraction. Going to a muzzle device that did not increase gas back pressure solved the problem.

Note: The Spider worked fine on other AR's; just this one had the problem.

quote:

Originally posted by MrMcGoo:
PS: On further thought, bottle neck cases are always annealed. However, there can be differences in powders used, annealing techniques and case thicknesses.

Remington 223 has lower pressure limits (~55K psi) while 5.56 has higher pressure limits (60K psi.) Higher pressure cases are frequently built differently to accommodate the higher pressures.

LC 5.56 cases are thicker than commercial .223 brass. Add in the QA\QC variances and it very well could be just that part of that case of ammunition. If the rifle in question was over gassed I would expect it to malfunction with numerous different types of ammunition. I await further information and a possible result.

Some more things to think about. I believe the rifle may be equipped with a Battle Comp compensator which is a more closed design than many others.

quote:

Originally posted by SgtGold:
LC 5.56 cases are thicker than commercial .223 brass. Add in the QA\QC variances and it very well could be just that part of that case of ammunition. If the rifle in question was over gassed I would expect it to malfunction with numerous different types of ammunition. I await further information and a possible result.

Actually, they are not and it's quite well known in competition circles. LC brass is thinner so they can pack more powder. One thing though is that the LC brass receives two strikes on the head to toughen it up more.

I discovered how thin LC brass was compared to Winchester when I inadvertently used Winchester brass for a super-max load I had developed in LC brass. First thing I knew, popped primers. The joys of mixing components at the bleeding edge.

In 7.62, it's the reverse, the MIL brass is a lot thicker than commercial brass.

It may be worth a call or an email to Federal to inform them of the issue and request their opinion. They will need a full description of the ammo including a lot number. They may also want the barrel length and manufacturer, gas port size and location. They will probably want the remaining rounds sent in as well.

Just because a primer wasn't flattened or backed out doesn't mean that there wasn't some over pressure for a milisecond.

I once had a "starter" load per a reloading manual have difficulty extracting with stretched cases. Further research showed that I was just over the powder manufacturer's maximum powder weight for that cartridge and bullet weight. Powders get reformulated from time to time which changes the relevant loading data.

Bill

- ^^ Mr. Magoo is right, notify the manufacturer of the issue.

-Most, if not all barrels are over gassed to run almost any type of ammo. Installing an adjustable gas block and tuning it to the ammo used will resolve the issue.

- the annealing marks left on the case is not an issue...military ammo is not polished after the annealing as it adds another step that equates to time/money in the manufacturing process (most commercial ammo is tumbled once after annealing and then loaded)

-the brake may be causing the issue by increasing the pressure int he weapon when the bolt is trying to rotate and travel rearward....simply swap it out with a standard birdcage flashider/compensator and see if the gun does it again. (cheaper and easier to change the brake than the gas block)

Updated at bottom of first post.

Didn't see it mentioned, but if the rifle had previously been functioning well, my first thought would be to scrub the heck out of the chamber.

Curious if the officer cleaned his rifle between using the "old" ammo which didn't work well, and the "new" ammo that did.

Also, annealed cases would be softer, increasing case expansion and the grip of the case on the chamber. Not certain if this is true, but wouldn't annealed cases be MORE difficult to extract, rather than easier?

I would be very surprised if the factory ammo is out of spec. Has it been tried in another rifle?