AR bolt sticking inside carrier?

[ynososiduts 0]

I took my newly built AR to the range for the first time and have a weird problem. I'll get a light primer strike, pull back the charging handle and manually cycle a few rounds that'll all be lightly struck. After manually cycling 4 or 5 rounds that FTF I'll eventually get a round that'll fail to eject. When I go to separate the upper from the lower I noticed the bcg was pushed back into the buffer tube a bit past where the upper receiver ends, necessitating pushing out both takedown pins. After getting it apart I can manually push the carrier forward, put it back together and it'll fire a few more rounds before not firing the next. Any ideas? The bolt seems to be getting stuck in the extended position causing the firing pin to not push into the primer far enough.

[NYMetsFan86 9]

First, when the carrier gets pushed back is the BCG jammed and hard to eject the round using the Charging handle? If so could be round not seating in the chamber. If your BCG will move forward inside the upper with the gas tube removed, than check and make sure there is no burring on the portion of the gas tube that sits inside the gas key. Also check to make sure your gas tube aligns properly with the gas key.

 

You can use process of elimination if you want. Does the BCG slide freely and seat with no gas tube? Does a round seat in the chamber if you drop it in manually? Did you examine the bolt face?

 

I'm sure you will have a billion suggestions on this thread. GL!

[jackandjill 683]

I would check the buffer tube for any hard play.  Push it in manually and see if it comes back to position properly. Check to see if its installed properly and all the way in. Also check for any dents or scratches inside the tube.

[ynososiduts 0]

First, when the carrier gets pushed back is the BCG jammed and hard to eject the round using the Charging handle? If so could be round not seating in the chamber. If your BCG will move forward inside the upper with the gas tube removed, than check and make sure there is no burring on the portion of the gas tube that sits inside the gas key. Also check to make sure your gas tube aligns properly with the gas key.

 

You can use process of elimination if you want. Does the BCG slide freely and seat with no gas tube? Does a round seat in the chamber if you drop it in manually? Did you examine the bolt face?

 

I'm sure you will have a billion suggestions on this thread. GL!

The whole BCG moves freely in the upper/buffer tube, and the bolt face looks like any picture I've seen in the internet.

[ynososiduts 0]

I would check the buffer tube for any hard play. Push it in manually and see if it comes back to position properly. Check to see if its installed properly and all the way in. Also check for any dents or scratches inside the tube.

I did notice the stock was a touch loose at the range.

[jackandjill 683]

I did notice the stock was a touch loose at the range.

Take the upper off. And manually push the bcg into the buffer tube and see if it comes out fully on its own (make sure you do it safely). Basically, you are checking to see if there is anything preventing the buffer spring operating properly and/or there is resistance elsewhere preventing bcg / buffer to work together. 

 

Also try a different upper /bcg (if you have one) with this lower. 

[SJG 253]

Maybe a gas tube problem. Check to make sure the gas tube assembly is good to go. Also make sure the bolt is lubed up.

[DanMarvel 9]

Post pics? Maybe others can spot the problem visually.

[Vlad G 345]

Also, your thread title says bolt sticking inside carrier? Do you mean that, or did you mis-describe the problem?

[ynososiduts 0]

Post pics? Maybe others can spot the problem visually.

 

I would but I'm awful at taking pictures and it looks pretty much exactly like any AR15 BCG I see.

Also, your thread title says bolt sticking inside carrier? Do you mean that, or did you mis-describe the problem?

Maybe...? I'm new to the AR15 game. The locking lugs seem to line up when I hand cycle the BCG in the upper when it's not on the lower. I can push the carrier in all the way without the bolt so the gas key is seemingly lined up. When it's firing it just seems like the bolt isn't turning and pressing into the bolt all the way. 

[Vlad G 345]

The bolt's movement is limited by the cam pin. I don't know what you mean by the bolt turning all the way or pressing all the way into carrier, it shouldn't. The bolt rotates about 25 degrees and moves back only as much as the cam pin moves back. If it moved "all the way" the bolt lugs would hit the carrier and that would be bad for them.

 

What ammo are you using? Does the ammo plunk freely into the chamber (if you take out the carrier) and does it fall out freely if you tip the barrel muzzle up? With the carrier out of the gun, does the bolt pivot freely inside the carrier (or as freely as the cam pin allows)? It shouldn't take a lot of hand pressure to make it move.

 

Take some pictures of the carrier group outside the gun and on your ammo, both new rounds and maybe some fired brass and post them.

[High Exposure 5,664]

Also, the firing pin is floating in the AR platform. You will get a tiny dimple on the primer just by charging the rifle - it is not a light primer hit.

[ynososiduts 0]

The bolt's movement is limited by the cam pin. I don't know what you mean by the bolt turning all the way or pressing all the way into carrier, it shouldn't. The bolt rotates about 25 degrees and moves back only as much as the cam pin moves back. If it moved "all the way" the bolt lugs would hit the carrier and that would be bad for them.

 

What ammo are you using? Does the ammo plunk freely into the chamber (if you take out the carrier) and does it fall out freely if you tip the barrel muzzle up? With the carrier out of the gun, does the bolt pivot freely inside the carrier (or as freely as the cam pin allows)? It shouldn't take a lot of hand pressure to make it move.

 

Take some pictures of the carrier group outside the gun and on your ammo, both new rounds and maybe some fired brass and post them.

 I'll try to take pictures when I get home. The carrier moves all the way up without the bolt. Ammo was a mix of federal and Tul, both go into the chamber and fall out without any sort of force. By all the way I mean as far as the cam pin allows. It did feel a little tight when I took it apart last night. I had to pull on the fire pin to get it out too which seemed odd.  

[Vlad G 345]

Of course you have to pull the firing pin. It passes through the cam pin so you can't get the cam pin out with the firing pin in it, which means you can't get the bolt out. While you are taking pictures, take a pictures of the bolt removed from the carrier as well. 

[ynososiduts 0]

Pictures! http://imgur.com/a/QwX1P That brass fouling on the bolt face doesn't look nearly as bad in person as it does in the picture. 

[JohnnyB 4,325]

All those FTFs sound like the hammer spring is installed backwards. Worth a check before we blame the upper.

[Vlad G 345]

Pictures! http://imgur.com/a/QwX1P That brass fouling on the bolt face doesn't look nearly as bad in person as it does in the picture. 

 

I'm a bit concerned about the wear on the bearing surfaces of the carrier. I have carriers with 25k+ rounds with less wear then that.

[JohnnyB 4,325]

I'm a bit concerned about the wear on the bearing surfaces of the carrier. I have carriers with 25k+ rounds with less wear then that.

I noticed that as well in the third pic down!

[ynososiduts 0]

All those FTFs sound like the hammer spring is installed backwards. Worth a check before we blame the upper.

 

I kind of feel like an ass, but the spring was indeed backwards. That explains the FTFs. 

[JohnnyB 4,325]

You will find that was all that was wrong! I know since I did the same thing! I had all the symptoms you had and that spring was the problem!

[ynososiduts 0]

I'm a bit concerned about the wear on the bearing surfaces of the carrier. I have carriers with 25k+ rounds with less wear then that.

 

 

I noticed that as well in the third pic down!

 

 

The pattern is the same on both sides and on the top by the gas key. It looks the same as the wear on the rails on the slides of my pistols after a few hundred rounds too. Could running it too dry be the cause? Or just the cheap PSA finish?

[ynososiduts 0]

You will find that was all that was wrong! I know since I did the same thing! I had all the symptoms you had and that spring was the problem!

 

You would think if it fired one round it would fire all rounds. 

[JohnnyB 4,325]

You would think if it fired one round it would fire all rounds. 

Nope, It would fire 1 out of 3 or so all with light primer strikes!

[JohnnyB 4,325]

The pattern is the same on both sides and on the top by the gas key. It looks the same as the wear on the rails on the slides of my pistols after a few hundred rounds too. Could running it too dry be the cause? Or just the cheap PSA finish?

Combination of the two. Not to worry, the BCG is fine. Just keep the lubed! The spring was the cause and a lesson learned!

[ynososiduts 0]

Combination of the two. Not to worry, the BCG is fine. Just keep the lubed! The spring was the cause and a lesson learned!

Yup! Thank you, and everyone else. I'll update y'all if it turns out that wasn't the problem.

[tattooo 220]

Sounds good

[raz-0 1,259]

I'm a bit concerned about the wear on the bearing surfaces of the carrier. I have carriers with 25k+ rounds with less wear then that.

Yeah look at the finish on the gas key too.

 

Makes me ask if the right buffer is being used, or if it is trying to jam the carrier too far into the buffer tube and that's what's causing those three areas of wear.

[Vlad G 345]

That's a good point, some of that wear is really jittery. What kind of buffer tube are you using (rifle or carbine), what buffer, and what recoil spring?

[ynososiduts 0]

That's a good point, some of that wear is really jittery. What kind of buffer tube are you using (rifle or carbine), what buffer, and what recoil spring?

I just bought an AR-Stoner 6 position milspec carbine buffer tube kit off midway. I've been handling the bolt and pulling back on the charging handle like crazy. I think its just a cheap finish. I also don't think it was lubed enough for the first 70 rounds I put through it.

[JohnnyB 4,325]

As long as your upper is also a carbine length you are fine! Trust me, the spring was the whole issue. You are also correct on the cheap finish and lube issue. My mind went every which way

after my day at the range with that rifle. I actually bought it as a complete rifle in a F2F sale. I was not told by the seller that he bought it as a kit! I figured that one out after I tore it down and found

the hammer spring backwards. I have had that rifle at the range many times since with ZERO FTFs or FTEs.