View Full Version : Bolt Not Fully Seating Round Into Chamber (Out Of Battery)
Scorpaznatica
10-03-11, 13:15
I searched around and I am having trouble finding a definitive cause or solution to the issue I am experiencing. If I missed something, then I apologize for creating a superfluous thread. Feel free to link me to existing threads if they apply.
The issue:
I built the rifle a couple of months ago and have since put about 500 rounds through it. The first 400 or so went through flawlessly. More recently, the bolt seems to cycle, eject the casing, grab a new round, and then get stuck about a half of an inch short of closed. It started doing it once or twice in each 20-rd mag that I put through, but now it's doing it on almost every round. If manually pull the charging handle back a bit (not so far as cause a double-feed) and then sling-shot it, it chambers the round the rest of the way and goes all the way into battery just fine.
If I lock the bolt back and manually place a round into the chamber, it gets very stiff and difficult to push in for the last 3/8" or so. It's almost as if the casing is just too large, or the chamber bore is just too small. It didn't seem to have any issue with this in first few hundred rounds through it.
The rifle has been cleaned after every hundred rounds or so, and re-oiled before its next use. Any advice or suggestions on what could be causing this, or how to fix it?
The rifle:
Lower:
PSA Stripped Lower Receiver
PSA Magpul Lower Parts Kit
Upper:
BCM 16" Carbine-Length Upper Receiver Assembly
BCM Gunfighter Mod 4 Charging Handle
BCM Bolt Carrier Group
saddlerocker
10-03-11, 13:41
Im no expert at all, but did you try other mags?
You said they were 20 rounders? What brand?
Did you change brands or types of ammo? Did you really scrub the chamber or just swab it and oil? I've seen this happen on other rifles and it's always been something in the chamber.
Yes... which ammo and mags??
If I lock the bolt back and manually place a round into the chamber, it gets very stiff and difficult to push in for the last 3/8" or so.
"push in" with what?
Belmont31R
10-03-11, 23:33
If you lock the bolt back to the rear, insert a loaded mag, and then press the bolt catch (to release the bolt) what happens?
It almost sounds like it is short-stroking but to be honest I am having a difficult time following your post.
1. What kind of ammo are you shooting?
2. What kind of magazines are you using?
3. When you say "build" did you simply drop a lower onto an upper and install the remaining parts or did you do more?
Scorpaznatica
10-04-11, 07:55
Im no expert at all, but did you try other mags?
You said they were 20 rounders? What brand?
20-rd PMAGs with 10 rounds loaded in each, so I don't think it's a magazine issue. As I said, the bolt is grabbing a new round and carrying it into the chamber just fine. The problem is that it can't seem to get it the last half-inch or so.
Did you change brands or types of ammo? Did you really scrub the chamber or just swab it and oil? I've seen this happen on other rifles and it's always been something in the chamber.
I have been using mostly cheap range ammo, such as Brown Bear and PMC X-Tac, but I've also tried it with mid-range stuff such as Winchester 5.56 and Federal AE XM193. This is my first AR, so it's possible that I am doing something wrong with the cleaning, but I'm not new to rifles in general. The 3 times I have cleaned it, I have sprayed the chamber/barrel with aerosol CLP, then wire-brushed, then run patches through with solvent, then cleaner, then a final lube. I also spray and brush the BCG. Should I be doing more during a simple post-range cleaning?
Yes... which ammo and mags??
See above.
"push in" with what?
In an effort to diagnose the issue, I attempted to seat a round into the chamber by hand. (Meaning place the nose in the chamber, and push from the rear with my finger.) The first half of the round went in fine, but when it got to the last half-inch or so, it got noticeably stiffer. Again, this is my first AR, so I still have a lot to learn. Perhaps this tight fit is normal, but it seems to be what is causing the problem.
If you lock the bolt back to the rear, insert a loaded mag, and then press the bolt catch (to release the bolt) what happens?
The bolt releases forward, grabs a round on the way, begins to chamber it, the round goes in straight, and then the bolt gets stuck about a half-inch shy of closed.
It almost sounds like it is short-stroking but to be honest I am having a difficult time following your post.
1. What kind of ammo are you shooting?
2. What kind of magazines are you using?
3. When you say "build" did you simply drop a lower onto an upper and install the remaining parts or did you do more?
If I understand short-stroking correctly, isn't that when the bolt doesn't travel far enough to the rear and is unable to catch the next round? This is not the problem. The bolt grabs the next round just fine, it just isn't able to drive it all the way into the chamber.
1. See above. Perhaps it's an issue with the cheap ammo, but as I said before, I had no problems with any of it in the beginning. It ran just fine for the first 300-400 rounds on the cheap stuff. Also, please correct me if I am wrong, but is it not safe to assume that a BCM rifle with all mil-spec components should be able to chew through just about any ammo without problem?
2. As mentioned above, I am using 20-rd PMAGs which are typically loaded with 10 rounds each.
3. Yes, by "build" I mean that I bought a stripped lower, installed all the components, then bought a completely assembled BCM upper and mated the two together. I also bought an assembled bolt carrier group from BCM and dropped that into the upper as well.
Change to some known good ammo and a new 30rd mag (USGI if possible).
C4
Measure your buffer spring to make sure it is within tollerance. Then check the installation of the botl catch to see if it is binding or not.
Then I would check for burrs in the chamber. Do you have a forward assist? Are you hitting it with your palm to get the bullet seated? If you do, can you extract the unfired round? If yes, then are there any gouges on the case or bullet itself? With the upper and lower seperated, how much force would it take to close the bolt and bolt carrier fully on a round?
As far as cleaning goes, shit can accumulate under the extractor and cause problems. If you can, remove the extractor and look for brass/steel shavings and other buildup that may be preventing the extractor from popping over the new case rim.
Clean your chamber good. Steel casings leave powder residual in the chamber due to it not expanding. This is definitely not a short stroke since it is pushing a new round in.
Thought of the buffer spring also comes into mind. It may not be strong enough to overcome the friction.
Quick question, did you have weight on the magazine as you were shooting?
Scorpaznatica
10-04-11, 11:08
Change to some known good ammo and a new 30rd mag (USGI if possible).
I'd like to stick to PMAGs just to keep things consistent, but if all else fails, I'll certainly explore this suggestion. Thank you.
Measure your buffer spring to make sure it is within tollerance. Then check the installation of the botl catch to see if it is binding or not.
Then I would check for burrs in the chamber. Do you have a forward assist? Are you hitting it with your palm to get the bullet seated? If you do, can you extract the unfired round? If yes, then are there any gouges on the case or bullet itself? With the upper and lower seperated, how much force would it take to close the bolt and bolt carrier fully on a round?
I will look into all of these things when I get home from work today.
As far as cleaning goes, shit can accumulate under the extractor and cause problems. If you can, remove the extractor and look for brass/steel shavings and other buildup that may be preventing the extractor from popping over the new case rim.
As with the above, I'll look into this when I get home.
Clean your chamber good. Steel casings leave powder residual in the chamber due to it not expanding. This is definitely not a short stroke since it is pushing a new round in.
Thought of the buffer spring also comes into mind. It may not be strong enough to overcome the friction.
Quick question, did you have weight on the magazine as you were shooting?
90% of the ammo I have put through this has been brass casing, so I don't THINK that's the issue. Other people have mentioned the spring as well, but I have a hard time believing that a brand new spring would be causing this. Although, defects do occur. I'll measure the spring and check tolerances and contact Palmetto State if that turns out to be incorrect.
As to the "weight on the mags"... I spent an hour or so on Saturday shooting from the standing position with the mags un-touched. The only "weight" on the mags were the Ranger Plates on the bottom, but that's obviously not anything to speak of.
You did say you couldn't push the round all the way into the chamber with your finger right?
Does the bolt close all the way (lock) without a round in the gun? If so, I'm with those who say clean the chamber. If not, look at the bolt (lugs) , can pin and the gas key and tube for battering.
I would not force it using the fwd assist and if you can't push a round in by hand, I don't see how the action sprinig can be the culprit.
Scorpaznatica
10-04-11, 12:18
You did say you couldn't push the round all the way into the chamber with your finger right?
Does the bolt close all the way (lock) without a round in the gun? If so, I'm with those who say clean the chamber. If not, look at the bolt (lugs) , can pin and the gas key and tube for battering.
I would not force it using the fwd assist and if you can't push a round in by hand, I don't see how the action sprinig can be the culprit.
Ok. So far, your post seems to be most in line with what I would have assumed was the issue. The bolt closes and operates normally without a round. As I said, there is a large amount of friction preventing the round from going all the way into the chamber. I cleaned it pretty well, though, and it doesn't seem to help. It's like the chamber is too small by a microscopic amount (which I doubt, given BCM's reputation for quality) or the casings are a hair too large. I supposed this is possible, but I have never heard of this happening. Anyone care to shed any light?
Look at the problem from cheapest to replace to most expensive. Right now, you are looking at the buffer spring, possibly the mag catch (doubtyful but worth a look), and then possibly a burr in the chamber. That is what I would look at, and in that order for this type of problem.
From:
TECHNICAL MANUAL
ARMY NO. 9-1005-319-23&P
AIR FORCE TO 11W3-5-5-42
RIFLE: 11 3/4 Inches (29 85 cm)
minimum to 13 1./2 inches (34 29 cm)
maximum
CARBINE: 10 1/16 inches (25.56 cm)
minimum to 11 1/4 inches (28.58 cm)
maximum.
Make sure the chamber is clean with your choice of gun solvent and a good chamber brush. After a good scrubbing see if the round can be placed in by hand. If it's getting further in or any easier then scrub it again. I'm guessing the ammo type might be dirtying up the gun.
http://media.midwayusa.com/productimages/large/423/423606.jpg
...The bolt releases forward, grabs a round on the way, begins to chamber it, the round goes in straight, and then the bolt gets stuck about a half-inch shy of closed...
Your symptoms are consistent with debris in the chamber. Even with a weak action spring, a clean chamber would allow the round to be seated with a light tap from the forward assist.
The other place to check for debris is the inside the barrel extension.
Another possibility is that some dimension with this lot of ammo is too large. Or the chamber is on the tight side and the previous lot was small. But it's more likely there is debris clogging up the works someplace
OP,
At this point I suggest that you contact BCM if you feel that the upper is the issue and let them resolve it.
For shits and giggles if you have access to another complete lower receiver I would swap it over and see if the same thing happens.
the round from going all the way into the chamber.
you do know that the rear of the cartridge should stick out of the chamber (but not out of the extension) right?
I am having the exact same problem on an AR pistol that I was shaking down for a friend. Will function fine for the first 6-8 shots and then fail to fully seat the next round. It has a Spikes Tactical pistol buffer kit, brand new. Using 30rd PMAGs. All premium, Federal brand .556 ammo. I too am going to try scrubbing the heck out of the chamber with some solvent and see if it helps. With the dirty operation of AR pistols it wouldn't surprise me if it was a dirty chamber. Some of the stuck rounds really needed some force to be extracted.
I don't think so and here's why. My 11.5" SBR with can mounted is also very dirty. I keep it lubed and clean it occassionally and I haven't had any issues and neither have those that shoot similar configurations with me.
Who makes your barrel?
I am having the exact same problem on an AR pistol that I was shaking down for a friend. Will function fine for the first 6-8 shots and then fail to fully seat the next round. It has a Spikes Tactical pistol buffer kit, brand new. Using 30rd PMAGs. All premium, Federal brand .556 ammo. I too am going to try scrubbing the heck out of the chamber with some solvent and see if it helps. With the dirty operation of AR pistols it wouldn't surprise me if it was a dirty chamber. Some of the stuck rounds really needed some force to be extracted.
I am not entirely certain who made the barrel. It is a 7.5" barrel with a pistol length gas tube. It was not built by me, only brought to me when my buddy bought it and it would only fire one round without failing. It formerly had a GSE recoil kit on it that totally worked like crap. The hammer would never reset after the first shot and would only fire when cocked manually. I replaced the recoil kit with the Spikes pistol buffer kit, replaced a beat up FCG with all new Colt parts. The gun worked great for about 90 shots and then the issue which is the subject of this thread started popping up. I am more than open to suggestions on how to solve it.
First, the 7.5" pistols are known to be some of the hardest to make run reliably. The reason I asked about the barrel is even though it may be marked 5.56 xxx whatever, some companies in fact use .223 chambers. So that could explain your failure to extract issue. Although I have to wonder because of what you're saying.
I'll be quite honest to say that I hate attempting to diagnose this stuff when you can't take everything into account.
I am not entirely certain who made the barrel. It is a 7.5" barrel with a pistol length gas tube. It was not built by me, only brought to me when my buddy bought it and it would only fire one round without failing. It formerly had a GSE recoil kit on it that totally worked like crap. The hammer would never reset after the first shot and would only fire when cocked manually. I replaced the recoil kit with the Spikes pistol buffer kit, replaced a beat up FCG with all new Colt parts. The gun worked great for about 90 shots and then the issue which is the subject of this thread started popping up. I am more than open to suggestions on how to solve it.
Question.
When you pull the charging handle to the rear and lock it, then insert a magazine with a round in it and release it, what happens?
I searched around and I am having trouble finding a definitive cause or solution to the issue I am experiencing. If I missed something, then I apologize for creating a superfluous thread. Feel free to link me to existing threads if they apply.
The issue:
I built the rifle a couple of months ago and have since put about 500 rounds through it. The first 400 or so went through flawlessly. More recently, the bolt seems to cycle, eject the casing, grab a new round, and then get stuck about a half of an inch short of closed. It started doing it once or twice in each 20-rd mag that I put through, but now it's doing it on almost every round. If manually pull the charging handle back a bit (not so far as cause a double-feed) and then sling-shot it, it chambers the round the rest of the way and goes all the way into battery just fine.
If I lock the bolt back and manually place a round into the chamber, it gets very stiff and difficult to push in for the last 3/8" or so. It's almost as if the casing is just too large, or the chamber bore is just too small. It didn't seem to have any issue with this in first few hundred rounds through it.
The rifle has been cleaned after every hundred rounds or so, and re-oiled before its next use. Any advice or suggestions on what could be causing this, or how to fix it?
The rifle:
Lower:
PSA Stripped Lower Receiver
PSA Magpul Lower Parts Kit
Upper:
BCM 16" Carbine-Length Upper Receiver Assembly
BCM Gunfighter Mod 4 Charging Handle
BCM Bolt Carrier Group
Scorpaznatica
10-05-11, 12:49
Question.
When you pull the charging handle to the rear and lock it, then insert a magazine with a round in it and release it, what happens?
I have had it do both. Just the other day I was shooting and I had both results take take place back to back.
The first result is that it slams the bolt home correctly, grabbing a fresh round on the way and seating it fully.
The other result is that it grabs a round, begins to chamber, and then gets stuck just shy of battery. When this happens, I am able to pull the charging handle back about an inch, then slingshot it, and it closes all the way.
Belmont31R
10-05-11, 12:51
It sounds like some geometry or angle is off somewhere, and you're not getting consistent/correct feed angles.
interesting......
you may be short stroking a bit, even though it gets behind the cartridge there is a fine line and if it just barely gets back then it is just not cutting it,
Your main spring is shot, or you're hitting the gas tube with the magazine pushing the carrier up a bit when loaded. if so bend it down a bit and make sure key is good and tight.
So, it's gotta be something like chamber getting dirty or main spring weak, if it was like a sharp edge it would have been worse in the beginning, but you never know.
*I always replace main springs after a few run-ins I have had. One day when I was done shooting I left the gun on the bolt catch for a week or two and that bastard was about an inch shorter later and it was the first time I had used it. It was from a mil supplier but springs are funny.
Like I mentioned previously. I would send the upper in and have it looked it. There are too many variables and too much guesswork happening.
Sorry to bring back an old thread.... but I seem to have sorted out the problem. The gun really liked lube and hated 30 round PMAGs. With a GENEROUSLY lubed BCG and a 20 round USGI mag it functioned flawlessly.
Change to some known good ammo and a new 30rd mag (USGI if possible).
C4
AFTER you scrub out the chamber...
the problem with steel case ammo is it doesn't expand as much as brass so there is leakage back into the chamber. this builds up and reduces chamber diameter.
not saying this is your problem but is symptomatic of the ammo you are using...
As for brass after steel case, M193 fired after a lot of Barnaul here.
http://i13.photobucket.com/albums/a264/artweaker/Troubleshooting/laquerbrasscomp.jpg
Scorpaznatica
03-28-12, 08:32
UPDATE:
I know this thread is a bit out-of-date, but I wanted to update it just in case anyone else is/was having the same issue.
I ended up sending my BCG back to Palmetto State Armory, accompanied by a letter explaining the issue that I was having. The service guy who received my package did some testing with my bolt and determined that it was indeed a faulty piece. They sent me a brand new one a week later free of charge.
The tech guy sent me a return letter saying that while rare, defects can occur during manufacturing. With that in mind, I'd suggest that anyone who has this problem contact the manufacturer of their bolt and see if it might still be covered under warranty.
I can say first-hand that PSA was very accommodating to work with and were very responsive in getting my problem fixed quickly.
Thank you to all of those who contributed to this thread the first time around. Your input was greatly appreciated!
Thank for coming back and updating us.
Ok, the OP and IQ posted while I was writing my post, and after I posted is when I realized this was an old thread, so I’m removing my post as it is useless. :( Wish I could just delete it.
https://www.m4carbine.net/attachment.php?attachmentid=16244&d=1365281740
I'm having a similar issue with a new rifle. Round is free to move but BCG is stuck until I slam the buttstock to get it to release. I'm getting ahold of the manufacturer next week.
I had this problem also, but it was not the gun. I had just reloaded 200 lake city brass and I had backed my sizing die out before starting. I had noticed that the sizing die was coming in contact with the shell plate on my LNL AP press so I backed it out about a 1/2 turn to clear the shell plate. I took those rounds out and one in 10 or so would not go into battery, hanging the BCG group a 1/2 from closing. I would have to work very hard on the charging handle to get it out.
I retrieved another AR from the house thinking I had a dirty chamber with the first one. And my second AR did the same thing. So I knew it had to be my reloads. I went back to my reloading shed and that's when I remember what I did with the sizing die.
Lesson to learn from this: do not go messing with something that is working fine just because you think it does not look right. I am just glad I had not reloaded a large number before finding this.
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