Troubleshooting...but fixed...tight chamber or other?

[rxer311]

So I finally got out to the range today with my AR pistol. Wanted to do a function check on it before I send in my form 1 to the ATF.

Put about 5 rounds through it, then about every other round I would get a failure to go into battery. It would cycle fine but was not going fully into battery. It didn't matter if it was a cycled round or if I was charging the first round. After it would not go into battery, it would be extremely difficult to extract manually.

I pulled out the BCG and inspected and cleaned. It started to get better but was still having issues with it.

After about 30 rounds went through it, it seems as though the problem resolved. Rifle was cycling just fine and the BCG was engaging smooth as could be. I put 140 rounds through it with the last 110 rounds being trouble free.

So it seems that everything seemed to work itself out.

I am still trying to figure out what was happening at first, though. I was thinking that maybe the chamber was a bit tight, but I doubt that would have just spontaneously fixed itself after 30 rounds.

Tight extractor? BCG just needed broken in? Just the breaking in process in general?

[Stone]

On new builds I will initially go a little heavy on the lube and cycle the rifle at least 100 times before I ever fire it to allow parts to mate up. There may have been to much initial internal friction slowing the BCG down.

[rxer311]

On new builds I will initially go a little heavy on the lube and cycle the rifle at least 100 times before I ever fire it to allow parts to mate up. There may have been to much initial internal friction slowing the BCG down.

So we are thinking just the initial breaking in process?

I have always heard that it may take a bit for a new build to break in...its just in the probably 15 or so rifles I have built over the years, this is the first issue I have had with a "break in."

Just glad it got to workin. Sending in my Form 1 shortly.

[Stone]

Pop the BCG out and check for excessive Cam Pin drag. There may be some tolerance stacking that should work its self out. Some builds run like race horses out of the gate and some seem to need a little tweaking. What caliber and ammo are you using?

[alamo5000]

I was having similar issues when I first did my SBR. I would highly recommend saving your brass and inspecting it when a problem arises.

My particular problem was happening because my carrier speed was too fast. It would pick up cases from the mag and slam them in, but it did so so violently that it bent the cases. Some were worse than others but they wouldn't go into full battery and were sometimes very hard to extract.

Before it was all said and done the problem was slight overgassing which caused a chain reaction of events. Problems were not on every shot. It depended on a lot of things such as rate of fire etc, but the solution was a heavier buffer. I also put an extra power spring in there and she hasn't missed a beat even once since.

The buffer alone would probably have done it but I put the spring in there as well and it worked great so I left it. Don't know the round count since then but it's very reliable now.

[rxer311]

Brass looks fine.

I think that Stone is probably right and it was a combination of tolerance stacking. I think there may have been some cam pin drag now that I think about how it was running. It just wouldn't go into battery and was hard to eject.

It only took about 30 rounds to start running and now that BCG is as smooth as can be.

[UWone77]

This is not an uncommon thing. Sometimes a new gun/parts need some rounds and a lot of lube to run. A lot of milspec parts especially seem to arrive bone dry.

I always run 3-5 hundred rounds through a gun before throwing it into "it work" pile.

[rxer311]

This is not an uncommon thing. Sometimes a new gun/parts need some rounds and a lot of lube to run. A lot of milspec parts especially seem to arrive bone dry.

I always run 3-5 hundred rounds through a gun before throwing it into "it work" pile.

I will be running a lot more through it. I just wanted an initial function test before sending in my paperwork.

It runs. I may need to do some tweaks, but I know that it won't be more than minor issues that can be worked out.

[rxer311]

I actually think it was a combination of a tight ejector and extractor. It loosened up and is now working.

[UWone77]

I actually think it was a combination of a tight ejector and extractor. It loosened up and is now working.

Not surprising. Just helped out a friend who had a similar problem you had. Once we got 200 rounds through the AR Pistol, it ran just fine. Lots of Lube helped as well. Everything he assembled was bone dry.

[SINNER]

Cam pin wearing into the upper. Just look for the first spot to show wear. It's almost always in the upper.