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Posted: 12/16/2012 4:39:30 PM EDT
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Hey guys..... I get to be the lucky guy whose new BCM upper isn't working. I'm sure it has nothing to do with the upper. Build quality is excellent and their service was top notch. Here's what I've got:
Gun doesn't appear to be short cycling. Bolt always locks back on an empty mag. Extraction is the issue. It is feeding a new round onto the semi extracted case. The empty case jams up into the upper, the new round gets jammed into the feed ramps and dented. It can be as bad as every second round. PMC seemed to be worse, but it was happening with AE 5.56 rounds also. The gun is a 14.5 carbine upper by BCM. It has a DD semi-auto chrome BCG. Buffer is a Spikes T2. I brought it back to my house to clean and inspect. I found nothing out of sorts. I pulled the BCG apart and found nothing unusual. I had some BCM bolt upgrade kits around, so I swapped the spring for the upgraded one. The old one had the spring insert, but the spring was much smaller/weaker than the upgraded part. I tried it with the O-ring, but I think it was too much. The extractor was chomping gouges into the cartridge rim. What do you guys think? Will the extractor upgrade solve my problem? I'm suprised to be having issues with a DD BCG. I didn't figure them to be a company that would provide a BCG with a weak extractor. Any chance it could be the T2? I have some standard H buffers that I could try, but I just can't see that. It always ran finne with my PSA M4 carbine upper, though it was a 16" |
| With the BCM spring, you do not need the o-ring. It's basically there for shits and grins. Start from the beginning so to speak. Put the BCM extractor spring in without the o-ring and put in the H buffer. I'm assuming you also have a stock buffer spring in there. See how that runs. |
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FTE with adequate gas could be???
Failure of extractor, extractor spring, or insert Dirty chamber Weak or short action spring (affecting the timing of the unlocking and extraction...) FTE could also happen with too much gas, and you'd either see marks from the extractor skipping over the rim or ripping the rim off. |
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Will do! I expected this gun to be a runner. I was a bit surprised to have an issue. I suspect the extractor spring will resolve it, but I'll bring a standard and H buffer with me next weekend.
FWIW: The chamber was cleaned before it was shot and there were no irregularities. |
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Quoted:
Hey guys..... I get to be the lucky guy whose new BCM upper isn't working. I'm sure it has nothing to do with the upper. Build quality is excellent and their service was top notch. Here's what I've got: Gun doesn't appear to be short cycling. Bolt always locks back on an empty mag. Extraction is the issue. It is feeding a new round onto the semi extracted case. The empty case jams up into the upper, the new round gets jammed into the feed ramps and dented. It can be as bad as every second round. PMC seemed to be worse, but it was happening with AE 5.56 rounds also. The gun is a 14.5 carbine upper by BCM. It has a DD semi-auto chrome BCG. Buffer is a Spikes T2. I brought it back to my house to clean and inspect. I found nothing out of sorts. I pulled the BCG apart and found nothing unusual. I had some BCM bolt upgrade kits around, so I swapped the spring for the upgraded one. The old one had the spring insert, but the spring was much smaller/weaker than the upgraded part. I tried it with the O-ring, but I think it was too much. The extractor was chomping gouges into the cartridge rim. What do you guys think? Will the extractor upgrade solve my problem? I'm suprised to be having issues with a DD BCG. I didn't figure them to be a company that would provide a BCG with a weak extractor. Any chance it could be the T2? I have some standard H buffers that I could try, but I just can't see that. It always ran finne with my PSA M4 carbine upper, though it was a 16" Sounds like your bolt is either kicking out the round before it completes extraction, getting under function of the ejector, or releasing the round too late in the cycle. Lube the ejector with a very liberal application of CLP and work it by pressing/depressing. |
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Quoted:
As I read this again it sounds like too much gas or weak/short action spring. The bolt is trying to extract too soon and gouging the cartridge rim. You may have to pull the front sight block and inspect the gas port in the barrel. It should be around 0.070" diameter. Anything much bigger can gtive you an over-gas situation that will begin the extraction before the cartridge relaxes and releases it's grip on the chamber wall. I had to fix one of my carbines with that problem. |
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