Failure to go into Battery on only first round.

AR/M4 AR Technical Discussion
1

I just got a Colt upper, BCG, and charging handle. The only thing I did after I purchased the upper was replace the extractor spring. The upper looks like it has seen very little use if any at all. After I completed my build and purchased some XM 193 and some Pmags I decided I would go out and finally shoot it after work…this is when I ran into a little situation. On the first round if I load up the Pmag and drop the bolt it won’t fully go into battery and some of the bottom part of the casing seems to protrude from the chamber and barrel. I then drop the mag and pull the charging handle slightly back and it go’s all the way into battery. After that It cycles like a champ. Is this a real big issue or something wrong? Or does it have something to do with it being a very new and not really “worn in”??? :confused:

Weapon Details: Colt BCG and 14.5 upper
On Target Tactical lower with CMMG lower parts kit
Bravo Company buffer tube, spring, and H2 buffer
Xm 193 Ammo and Magpul Gen2 Pmag

Any advice and help would be greatly appreciated!!! Thank you.

2

I would clean it really well including with a good chamber brush/mop. Also, is it lubed up? Make sure you have it lubed well.

3

Did you load the mag to the max? That first round could be in the magazine really tight. kwg

4

Do you have an O-ring on the extractor spring?

5

Just to verify one possibility - are you sending the bolt home with just moving the charging handle? If you’re loading 31 into the magazine and riding the CH slightly it can do something wacky like this.

6

What do you mean by “dropping the bolt”? Are you using the bolt release or the charging handle?

What kind of lube did you use on the BCG and upper?

7

PMAG’s will load 31 rounds into the magazine. A fully loaded PMAG with 30 rounds will result in the first round being the top right position.

8

Alright first off thank you for everyone who replied, now let’s see if I can answer some questions.

  1. I use Froglube and and the BCG is well oiled and the rifle has been cleaned.
  2. With the Pmags I only loaded to twenty and only one mag b/c I was just shooting it a little where I was at, today I’m going to get the chance to shoot much more.
  3. I don’t have a Oring with the extractor spring b/c I was told it would work fine without one.
  4. I use the bolt release (or ping pong paddle) to drop the bolt and that’s when it gets stuck. I then have to pull half way back on the charging handle and it fully seats the round. After that it cycles just fine, it’s just that first round that doesn’t want to co-operate.
9

Is this a Colt barreled upper, or is this a Colt Upper with a different manufacture barrel affixed? The 14.5’s from Colt are about as common as other 14.5" barrels installed into Colt uppers. It seems like the chamber might be on the tight side, or at least that ruling this out might be helpful.

10

It seems like it is has all the markings a Colt barrel would have. Well I think I found the issue. When I went to disassemble the BCG today the little plunger and spring fell out of the bolt when I took it apart. In my rage and fits of profanity I just ordered a new BCG from Bravo Company and said to hell with it.

11

I assume the “Plunger and spring” refers to the ejector and spring on the bolt face, correct ? If so they are retained by a small roll pin that you should also try to locate. I’ve never seen one back out on it’s own before, but there could have been something suspect about the parts to begin with. You can still reuse the old parts provided they aren’t damaged, so long as you replace the roll pin.