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Posted: 4/9/2006 3:40:22 PM EDT
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Mega Lower CMT Upper/Bolt/Bolt Carrier/Charge Handle/LPK Denny's Guns Recon barrel (fitted CMT bolt) el cheapo M4 stock/spring/H buffer Fired about 300 rounds today, nearly all of which was WWB. Some of the spent brass would get stuck between the charge handle and the bolt, some would just not eject (occasionally causing other jams). Bolt wouldn't lock back every time on an empty mag (no rhyme or reason to which mag it did this on). I have inspected my gas block and I don't seem to have any gas leaking out of the front. The gas tube is NEW and shouldn't be leaking out of the rear. The gas key is still properly staked and carb cleaner only comes out of the gas port when I spray it in the key. The bolt has a blue insert. I checked that the gas port on the barrel was clean before installing the barrel. The only thing I can think of that I may have done wrong was to not clean the Bolt and Carrier before use, but they weren't that gunked/lubed up when I installed them. Some sort of malfunction would occur maybe 30% of the time. I originally thought it sounded like a gas leak problem (short stroking, correct?), but I don't see where gas is leaking from and my gas key is still good to go. I now have no idea what the deal is and would REALLY appreciate the help as this is my first AR and the first trip to the range didn't go so hot. Thanks! |
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The bolt looks entirely okay. I have three gas rings and I made sure that they weren't aligned. Everything on the gun is NEW so I can throw out worn parts. I got my stock from TheTic00 in the EE. It's a cheap, no namer. Now that I go look at the buffer, I see three marks from the receiver extension retaining pin (I think that's what it's called). Am I looking at swapping recoil springs/buffers or getting a whole new stock altogether? Thanks for the help...I really want to chase the demons out of this thing because it was a hoot to shoot when it was running right. |
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FIXED! AAR: We removed, cleaned and lubed the bolt and bolt carrier. The bolt was moving freely in the carrier (like it could drop-out without the cam pin in). A one piece gas ring gave us the "normal" amount of tension. While we had the bolt out, the standard extractor spring was exchanged for a HD spring/black insert (never a bad thing). Hooligan's CAR buffer (not an "H" as described above) seemed a little light. Pulled apart, it had the three counter weights, but it still didn't seem "right". It looks as if each one of the weights were just a tiny bit short...making the whole assembly not quite up to snuff. Put everything back together and ran about 75 rounds of WWB/Q3131 through with five known-quality and functioning mags loaded to 1/2 capacity. Zero FTFs/FTEs, and the bolt locked back every time. Replaced the buffer with a standard-weight CAR buffer out of a Magpul M93. Ran about 75 rounds of WWB/Q3131 through again. Zero FTFs/FTEs, and the bolt locked back every time. Replaced the lower with a RRA A2 buttstock and standard rifle buffer. Ran about 75 rounds of WWB/Q3131 through. again Zero FTFs/FTEs, and the bolt locked back every time. Back to the original lower, but this time we put in a 9mm buffer. Ran about 75 rounds of WWB/Q3131 through again. Zero FTFs/FTEs, and the bolt locked back every time. However...watching the carrier cycle through the ejection port, things seemed to be slowing down significantly. I believe Hooligan ran through another two full mags (I wasn't paying attention anymore, as I was getting tired of the raining brass  ) with the original buffer in place at this point, as he said totaled out at 360 rounds. Guess what? Zero FTFs/FTEs, and the bolt locked back every time.Bottom line: While we never got a chance to test with the 3 piece gas rings and a heavier buffer, it looks like the problem was too much gas too early in the cycle. The helical gas ring solved the blow-by. Hooligan will be ordering a heavier buffer (a legitimate "H" buffer) to slow the action down just a bit more, but not so much as the 9mm buffer. While this may seem like a solution in search of a problem; this is the single part of unknown quality in his rifle, and I suspect was contributing to the short-stroking. Hooligan, it was great to meet you FTF, and I'm glad that your first build is now running 100%.  |
FMD, I really appreciate the help you gave me today. I don't think I ever would have guessed that my gas rings were out of spec. We wil have to get together again sometime and burn up some more ammo and so you can share more of your wealth of AR knowledge with me.  Going to go order an H buffer right now... |
 I can be a bit "talkative" sometimes, huh?
The "H" buffer is slightly (less than an ounce) heavier than a standard carbine buffer. Many suppliers carry them, and they are made by several different companies. IIRC, they were developed by Colt to prevent short-stroking and reduce the ROF of full-auto in the M4. ETA: AR-15 Buffer Comparison and FAQ @ BiggerHammer I believe that Adco sells the RRA made H Buffer, and their price is probably the most economical way to go: H Buffer @ Adco |
Nope, it took replacing the brand new three piece gas ring set that was a hair too small with a 1 piece gas ring. Other things, such as dirty components and a weak extractor spring, MAY have contributed to my problems but the gas rings are the likely culprit. |
Fixed things again. Seriously, your rifle was fine as far as being dirty. It could have used some lube, but we did that too. |
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FMD, I cleaned the gun today, and the bolt moves pretty easily in the carrier again. Not as easily as it did before, but easier than it did at the range. Everything looks good though and oddly enough, there aren't any more marks on my buffer... I still haven't ordered an H buffer yet as I'm waiting to get one from somewhere that I can get more gas rings and HD extractor springs from at the same time (I have a couple of friends that I helped get bit by the bug, so I figure they might need those). I'm waiting to hear back from Steve@Adco. |
Email is probably the quickest way... The bolt shouldn't be so tight that you can't move it, but not so loose that it would fall out of the carrier, either. The latter situation was very close to where you were at when we first pulled everything apart. |
Unless you can install your bolt without the cam pin, turn the carrier/bolt face down and the bolt free drops out, the rings are not the problem. In regards to the spring, just install a #60 O ring (read $.10 at any hardware store) around the extractor spring until the chamber breaks in. Really not going to point fingers, but often the lack of completely lubing (CLP) all of the bearing surfaces such as the upper bearing surfaces, and the receiver extension compounds, and fully cleaning the rifle before firing often leads to problems as the new/tight/rough surfaces polishes out/ breaks in threw live fire. Combine the upper advice with a new mag that too needs to break in, and you can have a nightmare on your hands that only hand polishing or additional live fire will resolve. |
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