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Posted: 11/4/2011 6:43:48 PM EDT
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***** Ok.. 95% of the problems stopped after switching to a standard carbine buffer.********
Only problem now is the bold does not lock back after the last round is fired. I was using a PMAG. I have heard of people have trouble with their bolt not locking back while using the BAD lever. Question is... what are the chances of this being the problem? Next time i shoot i will try with and without. Using Remington .223 55 grain, in a midlenth system with a carbine buffer, could it still be short stroking? Bolt catch appears normal, and still haven't tried 5.56 ammo yet. Any suggestions to look for would be highly appreciated. Thanks. Specifications: BCM BFH 14.5" Mid Length Upper Receiver Group w/ LaRue 12" Handguard (1:7 Twist) BCM Bolt Carrier Group (MPI) – Auto Spike’s Tactical Lower Receiver Spike’s Tactical enhanced lower parts kit Geissele Super Dynamic 3 Gun trigger Spike’s Tactical Carbine Buffer Assembly kit including ST-T2 buffer Pinned battlecomp 1.5 All parts are BRAND NEW That should be all pertinent information. Ammunition: Remington UMC .223, 55-Grain MC L223R3 American Eagle Tactical AE223 .223 Rem. 55-Grain FMJ. AE223J Finished a build about a month ago and shot it today for the first time and experienced some problems. Did not notice any problems the first 50 rounds. After that I noticed the bolt would not lock back after last round in magazine was fired using a PMAG. Bolt would lock back on a regular steel magazine sometimes; however, would not lock back like it is suppose to. (See picture) 
Gun would eject every spent casing, but sometimes the next round would get stuck on the feed ramps and dent the casing. (See picture) Kind of like a double feed Without a round in the chamber. This only happened with a pmag. 
Also, bolt would not always strip a new round out of the magazine using both PMAG and steel magazine. Would strip a round out of the magazine always using charging handle. (Gunfighter mod 4) Gun ejects at approximately 4 o’clock position. Thoughts: The gun is a midlength gas system and I was using .223 so I’m thinking its short stroking. I will try some 5.56 next week and have an extra S&W buffer and spring i will try. 
Any suggestions and or thoughts would be greatly appreciated. Help!!!!!! |
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Short recoil from the looks of it.
The Remmington ammo is not known for being that powerful. And, you have a heavy buffer, and a mid-gas system which does not have the overgas problem of many carbine gas systems. And, your gun is new, and in need of more rounds for break-in. If you are going to stick with the Remmington ammo, I'd try switching the buffer to a standard buffer. You can also try switching to some XM855 ammo to see if you can improve the action with the existing buffer, and shoot another 300-500 rounds to see if break-in improves operation. |
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You're shooting very low powered ammo in a minimally gassed and timed upper, along with a heavy "buffer".
And (IME) PMags have just a little more drag on the BCG than do standard metal mags, so if you're right on the fringe of short stroking, the PMags will show the symptoms first. The Spikes T2 is not a standard buffer setup, it doesn't use the sequence of moving weights so the buffering effect is minimal. IMO this contributes to short stroking issues as it fails to provide the correct delay in the return cycle of the BCG. I haven't used a BCM 14.5 mid, but other 14.5 mids I have shot work well with H buffers, or just a CAR buffer with lower power ammo. Might end up having to stick with metal mags with lower power ammo as well. I have the suspicion that shooting higher pressure ammo would solve the problem as well. Just from reading the reports and comments on the board in the past, it appears that the BCM 14.5 mids have a gas port on the minimal side, and seem to work much better with 5.56 power ammo. |
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I don't plan on shooting Remington ammunition. I only shot it today because that's what was available. I plan on ordering IMIM855C 1200 Round Case IMI 62gr M855 Ammunition. This ammo should be powerful enough to run the ST-T2 buffer right?
Ill order 5.56 ammo this week as well as .223 to try with the carbine buffer. What about the ST-T1 buffer? That would lighten it up too correct? If you guys care ill repost to advise you with results. Thank you all for responses. I appreciate it. |
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Quoted:
This ammo should be powerful enough to run the ST-T2 buffer right? .... What about the ST-T1 buffer? That would lighten it up too correct? Why not just use a standard part, like an H buffer? Anecdotally there have been tons of folks having troubles running the T2, which isn't terribly surprising since it's a reduced buffering "buffer", defeating the purpose of a buffer. Someone a while back had some video showing bolt bounce and IIRC the T2 buffered less than a simple CAR buffer. |
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Better idea, unless you are shooting 69gr plus ammo, which used slower burning powder and creates higher gas system pressure since the burn dwell high point is closer to the barrel gas port, just run the standard weight buffer that the carbine was designed to use.
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The gas system works off of buffer spring tension, the mass/weight of the buffer and B/C, and the amount that the gas port sees in pressure to unlock the bolt and cycle the action correctly.
When using standard ammo (55 to 62gr), the mass of the standard carbine buffer is all that is needed, and installing a heaver buffer slows down the cycle too much, and can cause short stroking (what you are getting now). In causes where you are using the 69gr ammo plus, it uses a slower burning gun powder than normal to get the bullet up to speed, which causes a longer burn with the pike of the burn dwell time closer to the gas port on the barrel, which in turn cause the gas system to see higher than normal pressures, causing the bolt to unlock too soon, and you need a heaver buffer to slow back down the unlock of the bolt to normal. Take a look at this link with the chart showing standard burn rate for the rifle powder of H335. If slower burning powder is being used, then the dwell burn pike is more the the right of the charts, creating more pressure back to the gas system. http://www.ar15.com/forums/t_3_66/266108_How_it_Works__The_AR_gas_operation_and_how_everything_works_in_harmony_.html In regards to your photo's of the dented cases, the bolt never made it back behind the rim of the mag loaded round, but instead stripped the round out of the mag via the center of the rim, and why you end up with the tip of the bullet into the chamber, with the bolt resting on the top middle of the case (not behind the rim). Simply, between the rough surfaces of the rifle breaking in, and the heaver than needed buffer for the ammo being used, the rifle was short stroking. Cleaning and lubing the upper bearing surfaces correctly with CLP will help the problem, and running the correct buffer for that ammo being used will solve the problem. |
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