AR Sponsor
Posted: 10/16/2009 5:17:21 PM EDT
|
My rifle is short stroking.
BCM Upper BCM A2 FSB BCM H-Buffer, Carbine Spring, Receiver Extension Daniel Defense 16.1" Mid-Length Barrel Young Mfg Chrome M16 BCG LaRue 9.0" Rail I will fire a round, the case is extracted and ejected without issue. The BCG will then either lock on an empty chamber, or have a failure to feed. That is to say that the bolt does not travel rearward enough to chamber a round. The rifle has approximately 500 rounds through it, this has been an issue for the entire time. Originally, I had an extra power carbine action spring. With that in, the bolt would not unlock after firing. I replaced it with a standard carbine action spring. I have tried putting the upper on a known good lower that has a carbine spring and standard buffer I have tried replacing the BCG with one that is known good I have tried various kinds of ammo, all brass, all good quality I have tried several known good magazines I have made sure the gas tube is not interfering with carrier operation I have run the rifle dripping wet, only lubed where needed, and everywhere in between The FSB was pinned to the barrel by Adco. The FSB is sitting almost perfectly straight, so cant is not an issue. There are only two things I can think of that could be an issue. 1) Defective gas tube This would be pretty crazy. It's pretty hard for a tube to be defective. The one currently in the rifle is from Denny at GTS. I will swap it with an extra RRA tube I have to eliminate this. 2) Gas leak at FSB After running about 120 rounds through it at the range, having the manually charge the weapon each time, the rifle began operating properly. I fired about another 150 rounds through it without problem. The barrel and FSB were coated with carbon. There is probably quite a bit of gas leaking at the FSB. The holes drilled for the FSB are higher on the barrel than I've ever seen. The holes are closer to the bore than what I've seen. The Adco pins may be smaller than average, so this might not be the problem, but if the FSB is being pushed up instead of being pulled down, it's probably leaking. If you guys really want me to, I'll beat the pins out and take pics of the holes. If the problem is with how the FSB is pinned, I could potentially be out another $300 for the barrel and another $100 for the pinning. What else am I missing? What should I try to fix it? If my worst fears are true, what options do I have? Here's a pic of the rifle, because no topic is complete without gun porn. 
|
|
Quoted:
2) Gas leak at FSB After running about 120 rounds through it at the range, having the manually charge the weapon each time, the rifle began operating properly. I fired about another 150 rounds through it without problem. The barrel and FSB were coated with carbon. Are you saying that the leak is plugged and now it cycles OK? Sometimes, this is exactly the way it happens. |
|
Given every "fix" you have listed.
My GUESS is #2. Call who you bought the barrel from and see what they say, over sized gas ports happen. Or you can contact ADCO, IF the intalation is bad (things happen) I'm sure ADCO will make it right. Sorry man, sounds like a nice build. Keep us posted. |
|
I thought it was fixed and it was just something that needed to be broken in, but it started short stroking again when I took it to the range again.
I'd like to nail down what the problem is before sending it to Adco. I'll probably end up sending it to them whether or not their FSB install caused it. I'd hate tearing the upper apart because I assembled myself, but I guess what needs to be done needs to be done. |
|
Quoted:
I thought it was fixed and it was just something that needed to be broken in, but it started short stroking again when I took it to the range again. I'd like to nail down what the problem is before sending it to Adco. I'll probably end up sending it to them whether or not their FSB install caused it. I'd hate tearing the upper apart because I assembled myself, but I guess what needs to be done needs to be done. I doubt you'll be able to get it figured out with out taking it apart. And waisting more ammo (dollars) shooting it isn't going to help you at this point, you have tried almost every thing. Call Adco, see what they say. They may want the whole thing to help sort out whats up. |
|
Sounds like you've gone a long way towards ruling out the usual suspects...
First things first, let's verify that the issue is truly "short stroking"... You describe the bolt as locking back on an empty chamber - assuming you mean that this occurs with a loaded mag in battery? If so, is the bolt "locking back" at the bolt catch (as it would with an empty mag), or simply ceasing momentum at some point before going back into battery with a fresh round? Is the bolt even beginning to strip a fresh round from the mag, or is it sitting atop the top round? Load a mag with one round, then fire it and see if it extracts/ejects and then locks back on the now empty mag.... If so, then the bolt is achieving sufficient rearward motion. If not, then you are accurate in saying that it is short stroking... If the weapon does lock back (consistently) on an empty mag, then you may have an issue other than lack of gas - such as drag on the bolt while in motion, which is slowing forward momentum... Any evidence of unusual wear or gouges/marks on the BCG or inside the upper receiver? You eliminated an out of spec BCG and Lower by swapping with known good units, so in this case the drag would likely be the fault of the upper. I've seen uppers compressed inwards / tweaked by vices or improper use of blocks, but not likely with the work being done by ADCO. Even though the equipment is top of the line (BCM) sometimes specs get outta whack, so take a look inside for evidence. Also do some hand cycling while paying attention to unusual points of resistance... If it is a gas issue, there are other possibilities besides leakage around the gas block (very unlikely, unless the gas block itself was far out of spec - regardless of the location of the pins, .750 is.750, pins aren't going to push a FSB away from a barrel that has a near friction fit...). I've had several rifles over the years with significant gas leakage around the FSB (enough to feel with a hand while firing) which caused no issues in cycling. You could have been bitten by an out of spec gas port on the rifle or the FSB, or a possible minor misalignment between the two (front/back since you said cant is not an issue). You should also proceed to swap the gas tube as it's a cheap/easy experiment that may save you further heartache... A couple of questions: How long (in terms of time - days and weeks, etc) has this been going on? How long ago did ADCO do the work? You stated "good quality brass ammo"... 5.56 milspec, commercial SAAMI, or mixed? Confirm that it is indeed short-stroking as detailed above versus some other issue then give ADCO a call. Assuming it's not been some ludicrous amount of time since the work was done, I'm sure they'll take care of this issue. One option you could consider (assuming a bad pin job that you can't get fixed) is going with a clamp on gas block (PRI, VLTOR, YHM, etc...) which would negate the effects of any out of spec pinning. I'd definitely look at swapping the $13 gas tube before you go that route, stranger things have happened and it's a simple experiment that will leave you with a spare if it doesn't work out... |
|
The work was done mid-July this year.
5.56, commercial, all of the above. I've shot American Eagle, Federal, mil-surp, Remington, probably a few others. No difference between them. When I say the bolt locks back, I mean it gets stuck at some point during chambering. The bolt will either not go rearward enough to begin stripping a new round (but remember it does go far enough back to eject) and will lock on an empty chamber, or the bolt will just barely catch the round but not have enough force to move it very far. I can't see any sort of abnormal wear on the carrier. When the magazine is empty, it occasionally may lock back, but it usually doesn't. Just like with firing, it may occasionally chamber a round, but it usually doesn't. I don't want to go with anything other than a pinned gas block. Even if it means spending $400 on a new barrel. |
|
Quoted:
The work was done mid-July this year. 5.56, commercial, all of the above. I've shot American Eagle, Federal, mil-surp, Remington, probably a few others. No difference between them. When I say the bolt locks back, I mean it gets stuck at some point during chambering. The bolt will either not go rearward enough to begin stripping a new round (but remember it does go far enough back to eject) and will lock on an empty chamber, or the bolt will just barely catch the round but not have enough force to move it very far. I can't see any sort of abnormal wear on the carrier. When the magazine is empty, it occasionally may lock back, but it usually doesn't. Just like with firing, it may occasionally chamber a round, but it usually doesn't. I don't want to go with anything other than a pinned gas block. Even if it means spending $400 on a new barrel. Sounds like you've got it pretty well nailed down to short stroking... Go ahead with the gas tube swap (unlikely, but like I said - cheap experiment). Then give ADCO a call - maybe point them to thread with a PM to bigbore here on the boards so he can see your details... If it's their pinning, I'm certain they'll take care of you. If it's not, you can guarantee they'll nail it down to a cause and let you know your options... ETA: Good Luck! I know it can be frustrating to pour time and money into good equipment with bad results - but you did the smart thing and went with good companies, so you can bet on a good outcome... |
| That tid bit about the extra power spring not unlocking and now you're short stroking with a standard spring means you're not passing enough gas. I've always been skeptical of gas leakage but if it's as bad as you say it is you might be on to something. Fortunately you went wit ha reputable company who will square you away. |
| please test gas tube with compressed air blow it in from blot carrier side feel air of barrel? . 2] do gas ring test / get new gas rings 3] paint white paint at gas key[white out -let dry] and shoot it next look bace for leaking ....for some bad news of my shorted too today the front bolt on the gas key opoped off -it is a Y/M bolt carrier too |
|
Quoted:
Quoted:
The work was done mid-July this year. 5.56, commercial, all of the above. I've shot American Eagle, Federal, mil-surp, Remington, probably a few others. No difference between them. When I say the bolt locks back, I mean it gets stuck at some point during chambering. The bolt will either not go rearward enough to begin stripping a new round (but remember it does go far enough back to eject) and will lock on an empty chamber, or the bolt will just barely catch the round but not have enough force to move it very far. I can't see any sort of abnormal wear on the carrier. When the magazine is empty, it occasionally may lock back, but it usually doesn't. Just like with firing, it may occasionally chamber a round, but it usually doesn't. I don't want to go with anything other than a pinned gas block. Even if it means spending $400 on a new barrel. Sounds like you've got it pretty well nailed down to short stroking... Go ahead with the gas tube swap (unlikely, but like I said - cheap experiment). Then give ADCO a call - maybe point them to thread with a PM to bigbore here on the boards so he can see your details... If it's their pinning, I'm certain they'll take care of you. If it's not, you can guarantee they'll nail it down to a cause and let you know your options... ETA: Good Luck! I know it can be frustrating to pour time and money into good equipment with bad results - but you did the smart thing and went with good companies, so you can bet on a good outcome... I've been looking closely at the FSB, and it doesn't look like gas could be escaping in large enough quantities to cause the sort of problem I'm having. Steve's expertise is reaffirming this. Good news is the barrel should still be good and fixable, because the FSB pinning shouldn't be an issue. Bad news is I mistakingly questioned Adco. Sorry Steve 
Something else is troubling me now. At the range last time, there was one time when I had the bolt locked back and inserted a full magazine. When I hit the bolt catch, the bolt pushed the round to the feed ramp and stopped. Tonight I was trying to test that. I locked the bolt back and loaded magazines. Every time I pushed the catch, the round would chamber normally. Every time I pulled the charging handle back and released, the round would stop partway up the feed ramps. When the rifle short strokes, about half of the time the bolt will strip the round, but the bullet will stop on the feed ramps. The other half of the time, the carrier would not travel far enough rearward to begin stripping the next round and would close on an empty chamber. Of course I just tried again manually charging the rifle a few times and it worked without problem. Now I think the rifle is just fucking with me. |
|
Quoted:
I've been looking closely at the FSB, and it doesn't look like gas could be escaping in large enough quantities to cause the sort of problem I'm having. Steve's expertise is reaffirming this. Good news is the barrel should still be good and fixable, because the FSB pinning shouldn't be an issue. Bad news is I mistakingly questioned Adco. Sorry Steve
There is nothing wrong with questioning anything, I just wanted to make sure you know your barrel is not ruined. |
|
Quoted:
Quoted:
Quoted:
The work was done mid-July this year. 5.56, commercial, all of the above. I've shot American Eagle, Federal, mil-surp, Remington, probably a few others. No difference between them. When I say the bolt locks back, I mean it gets stuck at some point during chambering. The bolt will either not go rearward enough to begin stripping a new round (but remember it does go far enough back to eject) and will lock on an empty chamber, or the bolt will just barely catch the round but not have enough force to move it very far. I can't see any sort of abnormal wear on the carrier. When the magazine is empty, it occasionally may lock back, but it usually doesn't. Just like with firing, it may occasionally chamber a round, but it usually doesn't. I don't want to go with anything other than a pinned gas block. Even if it means spending $400 on a new barrel. Sounds like you've got it pretty well nailed down to short stroking... Go ahead with the gas tube swap (unlikely, but like I said - cheap experiment). Then give ADCO a call - maybe point them to thread with a PM to bigbore here on the boards so he can see your details... If it's their pinning, I'm certain they'll take care of you. If it's not, you can guarantee they'll nail it down to a cause and let you know your options... ETA: Good Luck! I know it can be frustrating to pour time and money into good equipment with bad results - but you did the smart thing and went with good companies, so you can bet on a good outcome... I've been looking closely at the FSB, and it doesn't look like gas could be escaping in large enough quantities to cause the sort of problem I'm having. Steve's expertise is reaffirming this. Good news is the barrel should still be good and fixable, because the FSB pinning shouldn't be an issue. Bad news is I mistakingly questioned Adco. Sorry Steve
Something else is troubling me now. At the range last time, there was one time when I had the bolt locked back and inserted a full magazine. When I hit the bolt catch, the bolt pushed the round to the feed ramp and stopped. Tonight I was trying to test that. I locked the bolt back and loaded magazines. Every time I pushed the catch, the round would chamber normally. Every time I pulled the charging handle back and released, the round would stop partway up the feed ramps. When the rifle short strokes, about half of the time the bolt will strip the round, but the bullet will stop on the feed ramps. The other half of the time, the carrier would not travel far enough rearward to begin stripping the next round and would close on an empty chamber. Of course I just tried again manually charging the rifle a few times and it worked without problem. Now I think the rifle is just fucking with me. Friend of mine had a similar problems on a build he did (short stroking and FTF). He brought it over one night and I started going over the rifle. Started with the easy stuff just like you. Finally removed the upper and pulled the BCG and noticed his M4 barrel extension ramps were not lined up with his upper m4 ramps it was off just hair ... hhhmmmmm ... so I put the BCG back and pushed it forward slowly ... and it stopped at the barrel extension lugs and wouldn't go any farther unless i really pushed on it then it snapped into the lugs. Pulled back on it and it again was kind of stuck on the lugs .. had to really pull to get it to disengage the lugs on the extension. So the barrel had somehow slightly rotated while he was installing it into the upper. I took it apart the next day and aligned the extension with the upper ramps and reinstalled the barrel nut and hand guards. Works fine now .. no more cycling problems or FTF. Good luck OP hope this helps and you figure it out. |
AR Sponsor