AR malfunctioning

[masshole42]

Hello. I am new to this forum and am not sure if there is another post regarding a similar issue so my apologies if its redundant. Anyways I have a Bushmaster XM-15 that is having issues with fte and ftf. I never had problems before. Anyways I bought some Federal XM855 and M193 to shoot. I went through 4 mags(only 40 rounds since I live in MA) with no issues. Each round went bang and the bolt locked back on last round. My brother then loaded the rifle, fired the first round, then said it jammed. It was a fte. I proceeded to clear the malfunction and fire the next round. Another fte. Cleared that malfunction and then after that it was nothing but trouble. The malfunctions consisted of fte where the case would not fully eject and the bolt would jam halfway closed. The other malfunction was ftf where the case would eject but the bolt would close on an empty chamber. I tried cleaning and lubing the BCG and bolt with no effect. I am stumped. I'm familiar with the basics on my rifle, but in no way I am expert. The only modification I've done is a BCM extractor spring upgrade. Other than that everything I put on is purely cosmetic. It's a 16 in. barrel with carbine gas system. Stock buffer spring with a rifle buffer(came with rifle buffer, but I did purchase a carbine buffer). Any help would be greatly appreciated. Thanks.

[5pins]

It sounds like its short stroking. The first thing I would check would be the gas key and make sure its not loose.

[masshole42]

I did check the gas key and it was tight.This is the first time shooting 5.56 through my rifle, and I read that sometimes even though a rifle says it is chambered for 5.56 the measurements can be off. I'm hoping this isn't the case, and I don't believe it is since I was able to shoot a few mags reliably before the failures started to occur. My theory is that the bolt is moving too fast and the extractor is slipping off of the case causing it to not fully eject, and then in turn when the bolt attempts to close the spent case becomes jammed. I am no expert so that is just my theory. Would a heavier buffer or stiffer buffer spring slow down the BCG?

[landshark]

Few questions first:

1.) Is this a new rifle? As in these first 40 rounds through are the first rounds put down range?

2.) If question one is true, I would have to ask why throw in the BCM extractor spring?

3.) When you say FTE are you saying Failure to Eject (Brass does not fully leave weapon) or Failure to Extract (Brass is half/still stuck in the chamber)?

[AR-10]

Yes a heavier buffer will slow down the cycle, but that doesn't seem to be the problem.

How many rounds total have you put through this rifle?

If you are sure the gas key has a good seal on the carrier, I'd be looking at the gas rings on the bolt.

Something either wore out or came loose in the middle of your session, I doubt it's a buffer weight issue.

[AR-10]

I just realized you said you replaced your rifle buffer with a carbine buffer - you need to expand on that.

First of all, what buttstock do you have?

[Stickman]

if nothing was changed between it working, and handing it to him and it not working, check the carrier key for obstruction. I've seen primers pop out and get caught in there. They are a pain, and can be hard to see.

While its apart, check the rings and carrier key to make sure it is tight and hasn't come loose.

[Eric]

The only modification I've done is a BCM extractor spring upgrade. Other than that everything I put on is purely cosmetic. It's a 16 in. barrel with carbine gas system. Stock buffer spring with a rifle buffer(came with rifle buffer, but I did purchase a carbine buffer).

Did the malfunctions begin after you changed something? If you have the o-ring in place with the BCM extractor spring, try removing the o-ring.

Keep in mind that if you have a rifle size receiver extension (buffer tube) which typically has a fixed stock (A2, A1) you must use the rifle buffer. Rifle and carbine buffers are specific to their respective receiver extension. If you're looking at converting to a carbine setup, you need to change out the receiver extension, buffer and stock (and a few other small parts). Bushmasters are typically over-gassed. If run with the carbine stock, an H or possibly an H2 buffer is recommended.

Do you have a fixed front sight assembly or a gas block?

[landshark]

I just realized you said you replaced your rifle buffer with a carbine buffer - you need to expand on that.

First of all, what buttstock do you have?

+1
Its odd to me that Bushmaster would send out a weapon with a rifle buffer with a carbine buffer tube on the gun. If you XM-15 is the ones that I am seeing pics of with my google-fu, then unless you got it used it is unlikely that it had a rifle buffer in it. Not to insult your intelligence, but for reference:



Which do you have and then what type of buttstock like AR-10 said?

[masshole42]

I'll try to answer all of your questions: I bought the rifle used. Not sure how many rounds were put through it before I bought it but it looked as though not a whole lot. I have the standard adjustable butt stock that came with the rifle brand new(as far as I know). As for round count, I don't know exact numbers but I probably put close to 1000 rds or a little over through it. I bought the carbine buffer and BCM spring upgrade after doing some research because I wanted to shoot Tulammo(steel cased, dirty, underpowered, yada yada I know, but with those two changes my rifle cycled it flawlessly) I did not have the o-ring insert on the extractor spring when I had the malfunctions. As for fte, I'm not entirely sure. There were times when the case ejected properly, then other times it seemed like the case would extract from the chamber but not eject since the bolt would jam the case part way back into the chamber so that I am not 100%, sorry. It has the standard A2 front sight post. I did not change anything before the malfunctions occurred. I did check the gas rings. I extended the bolt all the way forward and stood it upright flat on the bolt face and the bolt did not recede back into the carrier so I'm assuming the rings are fine. If there is a better way to check the rings then I will try that.

[masshole42]

No offense taken. Believe me, I had to do research myself to figure it out haha. But yes I did buy it used and it was a rifle buffer that was in it.

[masshole42]

To clarify further, its a standard M4 style butt stock

[Stickman]

So you didn't pull the BCG apart and check the carrier key?

[AR-10]

It has an M4 stock but it came with a rifle buffer?

Pull out your action spring and buffer and take a pic, please.

[nub]

I had a bushmaster with a similar problem, turned out that the GB was leaking.. I figured it out when I noticed carbon on the GB.