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Posted: 8/10/2012 5:34:35 AM EDT
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My rifle is short cycling. It does extract and eject the casing but does not always strip a new round from the magazine, and it does not lock to the rear. Let me explain my parts:
I just built a .300 blackout. It has an 8" Noveske Barrel with a YHM 7.62 suppressor attached. All parts are mil spec with the following exceptions. Upper Receiver, Charging Handle, and Bolt Carrier Group are NiB coated. Also using a standard buffer and Remington 220 grain subs. The bolt carrier group is an M16 style NiB BCG by WMD guns. Now, I know its not a misaligned gas block. The gas tube pin is there. All this is in proper order. I tried a light weight buffer, a standard buffer, and a heavy buffer. Same results on all. Then I switched the BCG out for a standard AR15 type BCG. This fixed the problem. It cycled and locked to the rear. There was a noticeable difference in the smoothness and recoil. I also put the NiB bcg in my 5.56 AR and it cycled flawlessly, but those are a lot more powerful than the .300 blk. So the problem is the bolt carrier group. WHY? Its a brand new BCG. Does the weight difference between a M16 and AR15 bolt make that much of a difference? Is NiB crap? Does the BCG need a break in period? I am interested to see peoples theories on this. |
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Alot of people are reporting short stroking with the blackout
the round just doesnt have the same pressure as .223 as for the BCG it sounds like you swapped the BCGs just remember that both the BCG and upper reciever will wear and a new BCG might hang up a little until the high spots are worn down. try testing the diffrence using the charging handle and see if there is a diffrence in the pull. |
| Have you checked with Noveske? I have a CMMG 16" unsuppressed that WILL NOT cycle subsonics, and they acknowledge that. One suggestion was to drill out the gas port just a little. I didn't do that and settled for shooting supersonics only, but it's an option. I'm really surprised that yours won't cycle with a suppressor. |
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Quoted:
Then I switched the BCG out for a standard AR15 type BCG. This fixed the problem. It cycled and locked to the rear. Put the M-16 bolt in the AR-15 carrier, and the A-15 bolt in the M-16 carrier. Now retest the two and tell us if it's the M-16 carrier or the M-16 bolt that is the problem child. If the bolt, then double check the back bugle section of the bolt just off the tail to see if it was not milled correctly,and binding in the carrier channel for it (just compare it to the know good bolt if you don;t have a clue where to look). If that checks out, the suspect that the front of the bolt was not milled correctly, and it causing head space problems. On the carrier, two areas here if that is the problem. First would be leaking at the gas key to carrier/the gas tube not correctly indexed with the key, or problems with the hammer and the carrier, with the hammer being wedged between the bottom of the carrier and the top of the trigger/disco tails. |
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Ok. I will check the bolts, but if they were a problem, it should not cycle in the 5.56 upper either, and it does. The gas tube is center and has proper alignment with the gas key. I was an armorer in the Marine Corps, so I am not new to ARs or M16s. But this puzzles me. I appreciate everyone's comments. I know I don't know everything, and I am always open to someone else's ideas.
The gas rings are spaced 1/3 apart. The gas key is tight, not moving and properly staked. The gas tube is center of the receiver and meets little or no resistance when inserting the carrier only into the receiver. I measured all dimensions of the bolt that worked and compared them to the bolt that does not work with a dial caliper. All are the same +/- .001. The bolt and carrier look to be of good quality. I also tried the problem bolt with no lube and with generous amount of MPro 7 oil. No difference. Now, I just swapped the bolts in the carriers. They both worked cycled and locked to the rear on an empty mag. So, I reassembled the NiB bolt and fired it again. It showed improvement, cycling the rounds, but did not lock to the rear. This is after I put about 40 rounds of 5.56 down range with this bolt. Also, ejection patterns were abou the same with all combinations of bolts with the spent casings landing approximately 7 feet to the 4 o'clock position from the standing. I think all things are pointing are pointing towards this bolt needing a break in period. If this is true, I need to dump a hundred rounds of 5.56 through it because .300 blk is way too expensive to do that. I believe this is the case, because I was thinking of when I get a new phosphate coated Mil Spec bolt carrier group and rack the action several times, it sounds rough and you can smell the finish rubbing other metal. After several hundred rounds that is gone and the bolt is smooth. I really think this is the problem as this BCG was new out of the box when I put it in my rifle. Any thoughts? Also, whoever is running a NiB bolt carrier group in their rifle. Through your experience, do you still lubricate them? I know they advertise not to, but I just don't believe them. I haven't put enough rounds down range to tell though. |
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Slo, so you are saying that the new Bolt runs fine in the rifle in the semi carrier, and have weeded the problem down to just the new carrier alone (Looks like you are calling the entire B/C the bolt, and confusing me).
If so, then start off by dry fitting the new carrier without the bolt in the upper receiver. Is the key too wide and binding down the upper receiver track? Throw a bolt back into the carrier, and now while holding the bolt in the locked position (back), use compress air to confirm that the key is not leaking between it and the carrier. Even with the key allen bolts correctly tightened to 37inlbs, if the mating surfaces of the key to carrier is not flat and true, it going to leak badly and cause problems. Also, have not see this in a while, but if you do have to pull the key, always good to double check that the key gas passage lines up with the carrier gas passage If you find this the problem (or just the the side of the key is too wide for the upper receiver slot, the its time to pull the key and start lapping it in. ON the side of the key, it too can be lapped to reduce it width, but you are going to lose any plating/finish that it once had. And no, do not use the old key bolts, get new ones and install them instead. Or, just send the entire B/C back to have it replaced. P.S, unlike the Marine Corp where the parts that you used where Q/A checked no less than 4 times before you touched them, your dealing with civilian market parts that you have to be able to Q/A everything yourself (whole different ball game than just changing worn out parts to new parts like before; when you know that everything that you where using was in spec). |
| Sorry for the confusion. The entire NiB bolt carrier assembly does not work properly. I placed the NiB bolt in rhe standard carrier and it functioned. I also placed the standard bolt in the NiB carrier and it functioned. Only when the NiB bolt carrier group parts fail together. Its strange. I will check everything you just said though. You are very knowledgeable. Thank you. |
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This may or not be the problem, but I will put it out there.
Just like barrel bore and chambers, when a part is going to be plated, the plating will build up on the metal,and such metal parts have to be machined correctly for the over all thickness of the adding plating. Ways back, there was some Chrome plated B/C's that hit the market that where nothing more than just standard parts, that where just chrome plated. They caused problems to say the least, since now the bolt OD to B/C bolt channels where way too tight, and even the keys too wide with the plating to correctly fit the upper receiver slots without binding. I'll even take it a step farther, with one of the reasons that I dislike McFarland rings is they are so dam tight in the carrier on the bolt, that it can take up to several hundred rounds of the ring mating to the gas chamber section of the carrier before the bolt can glide correctly so the rifle can cycle right. So on that note, go back through the new B/C, and since you have a working B/C to compare it to, figure out the differences/ problem at hand. Granted that shinny is nice since you can see the fouling better to wipe it off, but if you have the upper bearing areas lubed correctly with CLP, then the fouling is not going to collect to either, being a plated or parkerized B/C. |
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