View Full Version : AR FTE

06-21-2010, 2:40 PM
Im have issues with what im thinking is a FTE causing a jam. The round looks like it spins around in the chamber but never exits and then jams on top of the nest round coming up into the chamber. Revently it has been spinning 180 and jamming above the bolt, IE the fired shell would be facing the rear above the bolt. Its a PITA to get the shell out when it does this, im wondering if this is an extractor spring issue or what else it could be. I did upgrade to a BCM extractor a while back and put about 500 rounds on since then.

06-21-2010, 3:17 PM
Try shooting one round at a time without the mag.
The round is extracting but bounces around in the receiver?
Ammo used is...?
What has changed since it shot well?

06-21-2010, 5:59 PM
sorry even when i shoot one round at a time sometimes its ends up sitting on top of the empty mag or halfway out the ejection port.

this is happening with PMC bronze, LC M193, and reloads.

Nothing has changed since this happened, so im wondering if its just a spring getting worn out and if so which is it so i can replace.

06-21-2010, 6:04 PM
Get some full powered 5.56mm in case it is short stroking.
Try different mags.
Did it work before the BCM extractor upgrade? If so, go back to the original.
Check out your ejector.
Oil the h*ll out of your bolt group.
Try cycling a magazine by hand, is it still an issue?
If it isn't short stroking, bolt group is oiled, ejector and extractor check out okay and it continues with other mags you could try a heavier buffer.

06-21-2010, 7:43 PM
would the lake city m193 be considered full powered?
Ill pick up some new mags and check it out.
It worked before and after the BCM upgrade, ill swap it out to eliminate that.
what would i look for in the extractor?
i can cycle it by hand with no issues.

06-21-2010, 7:48 PM
If you can cycle it by hand then I don't think it's the extractor or ejector.

06-21-2010, 8:31 PM
Yes, the point of cycling it by hand is to see if the gas system is related to the failure. If it works fine when it is hand cycled your extractor, ejector and magazine are likely fine. Oil it up a lot and see how it does with 5.56mm only. M193 is 5.56mm, PMC is weak stuff, and unless those reloads are yours we don't know how hot they are. Have you noticed any of these failures with the M193? If so, you could have a gas issue.

What buffer assembly are you using?
What length gas system?
What gas block are you using? If it isn't the pinned on standard pyramid one, eyeball it and see if it may be canted. If your using drop in handguards, it would be easiest to remove those and that way you can see how straight the gas block and the gas tube is.
Check your carrier key for looseness.

06-21-2010, 8:57 PM
thanks for your help josh, as for the questions,
im not sure the buffer assembly, its the one i got with it. Im pretty sure the rifle was a cmmg m4 16" but i got it at a gun shop complete.

I believe its a carbine since the 16" barrel

the gas block is the standard pyramid gas block.

ill fire off a few of the 556 rounds and get back to you on carrier key and if any of those rounds FTE.

06-21-2010, 9:08 PM
Definetly check the carrier key for looseness. If the gas block is the standard one there is lot less chance it was installed incorrectly but still check to see if it might be canted. These are likely aren't the problem but should be checked regardless.

Since you mentioned it is CMMG I am going to go ahead and guess they put in a regular carbine buffer. You can check by separating the upper and lower and looking at the buffer inside the lower. If there is nothing engraved on it than it is likely just a carbine buffer. And since it is a carbine system I am gonna go ahead and guess it is overgassing and the bolt is cycling before the spent round is ejected. Assuming the other stuff checks out I'd suggest picking up a heavier buffer. An H buffer should do it.

Here is a list of the buffer weights, if your rifle is overgassing and the actions are cycling too fast a heavier buffer will slow it down:
Standard CMT carbine buffer - 2.9 oz.
CMT H buffer - 3.8 oz.
CMT H2 buffer - 4.1 oz.
Armalite H3 buffer - 4.7 oz.
RRA 9mm buffer - 5.5 oz.
ST-X SS 9mm buffer - 6.0 oz.
ST-9X SS Extended 9mm buffer - 8.5 oz.
ST-SST - 7.0 oz.

06-22-2010, 12:20 AM
I checked the carrier key and it has about 1mm of play in it, im going to tighten it and re stake it.

The buffer is not marked at all, what i do notice is that the plastic (or whatever its made of) that comes in contact with the back of the rear of the buffer tube is being pushed into the buffer. It looks like its shaving off some of the sides and i can see little shavings in the buffer tube. Is this normal?

Liberty Rules
06-22-2010, 12:50 AM
I had the same problem a few years ago. It turned out that the gas key on the bolt carrier was leaking like a sieve--it was bad out of the box. I had a new key installed and staked and it solved my problem. No issues since then.

06-22-2010, 1:26 AM
Do you mean this piece here (http://www.calguns.net/OLL/OLL35.jpg) is making contact with the buffer and is having plastic shaved off? If so that sound like anything you should be worried about. Truth be told your rifle really doesn't even need that piece, it is called the buffer retainer. All ARs have it, but it is far from necessary for your rifle to operate.

Fix the carrier key definetly. This is an excellent thread on carrier key staking, you definetly want it turn out like the BCM/LMT/Colt photos: http://www.ar15armory.com/forums/AR-carrier-key-staking-p-t19144.html

06-22-2010, 1:08 PM
This is the part of the buffer tube im talking about, thanks for the pics of the stakes, mine looked like the bushmaster stake and i can easily back the screws out right now so ill be taking to that soon.