View Full Version : Help, my AR 15 keeps on jamming!!

Ruben Nasser
July 10, 2000, 04:53 PM
I have a Colt AR15 16" pre ban carbine, 1 in 9" barrel with an aftermarket muzzle brake. It jams with military ammo (full power 55 FMJ), Win or Korean good stuff that shoot beautifully in my friend's AR15s. This does not happen with other ammo (heavier bullets or reduced velocity). Seems like the typical stoppages of the early AR15 era accounts, because of too much gas pressure too early. The extractor just slips over the rim of the case or breaks it, leaving a stuck case in the chamber. Chamber is not rough, everything is new, clean, and in (apparently) excellent condition in the rifle, and I have exchanged with my friend's bolt, recoil spring and buffer, and it keeps on jamming. The last part I have to isolate is the gas system, could it be out of spec? How can I check it? Maybe the gas entrance drilled in the barrel is oversize? Can the muzzle brake be a cause? (I'm going to try without it, anyway). Any ideas wellcome!! Thanks!!

[This message has been edited by Ruben Nasser (edited July 10, 2000).]

July 10, 2000, 06:44 PM
Did you exchange with your friend's bolt or bolt carrier?

July 10, 2000, 06:44 PM
Did you exchange with your friend's bolt or bolt carrier?

July 10, 2000, 08:48 PM
Do some checking.If I remember right there is a adjustable gas system for your ar.If I find the ad I will post again.Might check brownells.

Age and deceit will overcome youth and speed.
I'm old and deceitful.

James K
July 10, 2000, 09:15 PM
It sounds like the gas port may be oversize. If the top is Colt, they should be able to supply the spec and you can check it out. I don't know how it could get out of spec (somebody goofed?) unless the rifle is used and a previous owner was playing around, messed up, and unloaded his problem. Another alternative is to take it to a good AR15 gunsmith. You might want to try looking in on www.ar15.com, (http://www.ar15.com,) which has a lot of info on those rifles.


Ruben Nasser
July 10, 2000, 09:28 PM
Thanks for your replys!! I exchanged the bolt and bolt carrier, double checked the recoil spring and buffer to make sure were the right ones (lenght, weight, etc.), and keeped on jamming. I think the gas system is the last remaining variable. Fulton Armory has an adjustable one, but it is frustrating not being able to solve this puzzle. I live in Paraguay, south america, and there are no qualified armorers around, and no way to take it back to Colt, thanks God is an easy rifle to "learn the internals". Is there anything I should look for when dissasembling the gas system? I can't find much info on gas tube and gas port diameters, etc.

4V50 Gary
July 10, 2000, 10:52 PM
Inspect the gas tube for cracks, non-factory holes and signs of crushing. Also check for non-factory bends (there are only two bends on a factory gas tube). Gas tubes are low maintenance items and about the only thing you do to it is replace it.

Since you eliminated the chamber and extraction is the problem, don't forget to inspect the extractor (is it clean, excessive buildup between extractor and bolt), moves freely (with blade of brass punch see if you can push it out). Also check the extractor spring.

Bartholomew Roberts
July 11, 2000, 09:37 AM
Ruben, if you have changed the bolt and bolt carrier, don't forget to check the headspacing again. Swapping bolts and bolt carriers between rifles can cause the headspacing to reach a dangerous state.

Ruben Nasser
July 11, 2000, 10:48 AM
Thanks, Bart, I did check the headspace before changing the bolt and bolt carrier. I've got the specs now for the gas tube and port. What if the port is oversize in my gun? Should I change the barrel?

July 12, 2000, 11:31 PM
There's a little aftermarket polyurethane thing that goes inside the extractor spring; adds more force to the extractor. You may also be able to find a stronger spring (or an inner helper spring). Check Brownells and Bushmaster.

If the gas port is oversize, it can be bushed, but that would take some careful work. Its a lot easier if its undersized. But it seems to me that if the gas port were badly oversized, you'd really have your fillings rattled by the recoil when the buffer impacts the end of the buffer tube. This is why I think you should try messing with the extractor first; easier and cheaper. Also, you might want to remove the extractor and look at it under magnification; make sure the hook part is properly machined, might have too open an angle.

[This message has been edited by Ivanhoe (edited July 13, 2000).]

Ruben Nasser
July 13, 2000, 04:56 PM
I 've checking how to take apart the gas system, and it's not that easy (besides, what if the port is oversize?). Maybe I'll polish the chamber a bit and then try to increase a little spring rate/buffer mass. What do you think?

July 13, 2000, 06:06 PM
The extractor check is good advice. Also, make sure it is a buffer spring for a carbine and NOT for a standard sized AR. That could cause some problems with full house loads.