View Full Version : 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
CAR-15 from an NFA lower. M-4 flattop, quad rail, 11.5" barrel, pneumatic buffer.
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/Tech%20Notes%20New/Tech%20Note%2048,%20Barrel%20Design,%20Heat,%20and %20Reliability,%20030824.pdf
Good Luck..
Jim
The Reaper
04-21-2008, 14:13
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
I'm thinking weak hammer spring or firing pin. Any other ideas?
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/store/ProductDetail.aspx?p=1591&title=AR-15%2FM16+PIGTAIL+GAS+TUBE Hope it provides an option for you.
Ambush Master
04-22-2008, 16:14
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?
The Reaper
10-22-2008, 11:31
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
Jack Moroney (RIP)
10-22-2008, 13:23
Final consensous...H-2 or H-3 Buffer?
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
Peregrino
10-22-2008, 13:33
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!
WRMETTLER
10-23-2008, 11:32
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.
Smokin Joe
10-23-2008, 16:31
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.
To add on what WRMETTLER stated, check the bolt carrier key to make sure it's not too plugged up with carbon or other debris. I've done some research the past few days on this, and build-up seems to be a primary cause from what I gather. Also, check the key/tube alignment by field stripping the bolt carrier group, then inserting it into the rifle, hold at a 45 degree angle, move the carrier flush to the rear of the upper receiver, and let it drop (charging handle latched of course). It should be a smooth operation. If binding occurs after cleaning, it could be barrel nut alignment, bent gas tube, or bent carrier key. Just another possibilty. Back in my lane. Out.
Every time it fails to fire, remove optic's and take 5 lb hammer and beat the upper till it complies with your demands, then re-oil bolt and re-chamber ammo, fire more rounds. If problem continues beat the lower into submission. sooner or later it wont jam anymore, or wont work at all, in the case of later return to manufacture and demand your money back.:lifter
82ndtrooper
10-23-2008, 20:18
Every time it fails to fire, remove optic's and take 5 lb hammer and beat the upper till it complies with your demands, then re-oil bolt and re-chamber ammo, fire more rounds. If problem continues beat the lower into submission. sooner or later it wont jam anymore, or wont work at all, in the case of later return to manufacture and demand your money back.:lifter
I did that with a Bushmaster, it seemed to work fine after the beating. :cool:
This weapon is "IG Inspection" clean. No carbon build-up anywhere.
I ordered an H2 buffer and a new buffer spring resterday. If that doesn't fix the problem, I'll look at other possible timing issues.
Thanks!
Justinmd
10-24-2008, 18:03
Your problem is bolt bounce. What you need is a buffer with a sliding countermass. A harder spring will not help (hammer spring or action spring).
We ran into the same problem on the first Masada, that's why the carrier has a sliding mass.
Basically as your bolt carrier slams home and trips your sear (which releases the hammer), the carrier then bounces back off the face of the barrel extension and pulls the gun slightly out of battery, and also doesn't allow full firing pin travel (thankfully). The hammer hits it at this inopportune time.
Grab a buffer and shake it back and forth, if you feel something sliding in there (usually a tungsten weight), then you should be good to go.
Let me know if you have any questions,
Justin
Your problem is bolt bounce. What you need is a buffer with a sliding countermass. A harder spring will not help (hammer spring or action spring).
We ran into the same problem on the first Masada, that's why the carrier has a sliding mass.
Basically as your bolt carrier slams home and trips your sear (which releases the hammer), the carrier then bounces back off the face of the barrel extension and pulls the gun slightly out of battery, and also doesn't allow full firing pin travel (thankfully). The hammer hits it at this inopportune time.
Grab a buffer and shake it back and forth, if you feel something sliding in there (usually a tungsten weight), then you should be good to go.
Let me know if you have any questions,
Justin
This one. Most full autos have some sort of anti bounce wieght in the bolt so it stays shut in full auto. Change the buffer to one with a sliding weight and it should fix your problem. Also if the gun isnt an original shortie or even if the barrel manf. didnt get the port size correct, it could cause excessive bolt velocity which could be causing the problems youre experiencing. If this gun is ran suppressed that may only aggrivate the problem. Its either port size and its getting overgassed or the buffer needs to be changed. Alost of this has been said but without knowing your manf. its hard to know gas port sizes and such. Theres only a couple companies that actually have the port size right for shorties. LMT, Noveske, Colt, are the few I know are correct. Barrels from bushmaster, RRA, and YHM, just to name a few arent correct and can result in beating the crap out of your gun along with the problems youve described. Hope this helps.
The H-2 buffer installation did the trick! My baby runs like a dream now! Thanks all!
The Reaper
12-15-2008, 12:18
The H-2 buffer installation did the trick! My baby runs like a dream now! Thanks all!
I thought so.
Happy blasting!
TR