CAR-15 Problems
 

I'm an SF Weapons man, but need a second opinion before I proceed further...

I built a CAR-15 from an NFA lower. M-4 flattop, quad rail, 11.5" barrel, pneumatic buffer.

The weapon function flawlessly in semi-auto, but when I flip it to full-auto, I get 3-4 rounds then a light primer strike resulting in a failure to fire. This only happens on full auto. Never encountered this type of problem before...

I'm thinking weak hammer spring or firing pin. Any other ideas?

226

If that doesn't fix the problem,,

1)swap out the buffer
2)check alignment of upper & lower & buffer
3)lap the bolt/carrier/upper for a couple hundred rounds

Also if the gas port position or barrel length was altered, the gas port size may need to be altered to account for the timing pulse..

ref:

http://www.armalite.no/downloads/Tec...,%20030824.pdf

Good Luck..
Jim

Sounds like the weapon is out of time.

Before I did anything else, I would pop in a 2xH or 3xH buffer and see if that fixed it.

Then consider the other dynamics of the timing.

Best of luck!

TR

Roger that fellas. When I return from Germany, I'll go through your suggestions step-by-step. Thanks!

226

Without being able to see the rifle first hand, or knowing the manufacturer(s) of each part, It could be the gas tube, or like you stated, the firing pin. Is the hammer spring seated correctly? Brownell's sells a pigtail tube that may correct the deficiency. Here is the site with a description of what it does.
http://www.brownells.com/aspx/NS/sto...GTAIL+GAS+TUBE Hope it provides an option for you.

Could it be weak Sear and/or Disconnect Spring(s) allowing the hammer to follow the bolt occasionally??

Final consensous...H-2 or H-3 Buffer?

Buffers are cheap. NFA lowers are not.

I would get both buffers, and start with the H2, though I suspect that it will run better with the H3.

Best of luck.

TR

We had buffer problems with ours in SVN, but it has been so damn long I cannot remember how the wpns folks resolved the problem. Seems to me that they boosted the spring strength somehow, but I cannot be sure. But then I am not sure what I had, or even if I had, for breakfast this morning:D

The H2 will be by far cheaper and easier to come by. Start with that. Also, when was the last time you changed the action/buffer spring?

Good times,
Blake

You have a timing issue. TR's suggestion for the 2xH buffer is a good place to start. You can also check out bolt carrier weights. There are a number of other drop-in aftermarket solutions, all of them intended to add weight/inertia to the reciprocating parts and delay unlocking. Gas system tweaks are more involved. I've used the pigtail; they work but will interfere with some handguards. My personal solution is a mid-length gas system (which doesn't help you with an SBR :p). Get the Brownells AR specialty catalog for a convenient reference. HTH

Toying with Gas systems/buffer weight/action spring strengths can quickly lead down the path to madness.

I would highly recommend going to an H2 Buffer and a good standard weight buffer spring first, and going from there.

My .02

Good times,
Blake

I'll start with the H2 and let you guys know the results. Thanks!

ODA 226
I am not a LEO or a MIL, and have very limited experience with automatic weapons. So take this information for what it is worth.
I purchased a NFA Bushmaster lower more than 20 years ago. It ran for a time, and then developed the identical problem you describe – 3 or 4 rounds fired full auto and then a light primer strike on the 4th or 5th round. I tried everything, and was never able to fix it. I finally just put the rifle away. It’s now the oldest safe queen I own.
I went shooting with Team Sergeant last year. While shooting, I asked TS if he had any suggestions to the problem. He gave me a standard buffer and spring from a rifle he changed to a collapsible stock, suggested I clean the rifle, lubricate it well and shoot it. He stressed that cleaning and lubricating are important.
His ideas worked. I ran 3 mags through the rifle the first time, and about 10 more since. Ammunition is too expensive to shoot more, and tell the truth, shooting it semi is more enjoyable. When I was single, it did have its appeal though.
I don’t think changing the standard buffer or spring had much to do with the remedy, as I’d changed them before. I do think the cleaning and lubricating the heck out of the it had everything to do with it. I really used a lot of Slip 2000.

If all else fails you can contact Ken or Tina Elmore at Specialized Armament Warehouse specializedarmament.com/ (add the www.)

ken@specializedarmament.com

or

(480) 940-7397

Ken and Tina are extremely knowledgeable and very .Mil friendly.