Posted: 2/28/2010 12:00:49 PM EDT
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CMMG,
We just received a new CMMG M4. Cleaned it up and lubed with CLP. Here's are the problems after 150 rounds. 1) Failure to feed the 2nd round. Sometimes you could shoot a string of 3 rounds but that's the best it would do. 2) Faliure to eject. Sometimes the spent round would be in the chamber and other times it would stove pipe. 3) Sometimes when chambering the first round the bolt carrier wouldn't go all the way into battery and lock up so tight that we had to bang the butt stock on the table. This would also happen sometimes after the first round. We tried 2 USGI and 1 Promag. These mags worked fine in the other AR's. The ammo was a assortment of Wolf, PMC, Winchester and reloads. The Wolf was a total failure in this rifle. All ammo worked well in the other rifles. It seems like the gas port is undersized but not likely, or the problem is on the other end in the buffer, spring or tube. The rifle looks real nice and appeared unfired. You thoughts please. |
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It sounds like a chamber issue. Give the chamber a good polishing out using a chamber brush, cleaning rod section, and cordless drill. Using a solvent, buzz for 30 seconds. Do not use wolf ammo with this rifle. I suspect once the chamber is cleared out, it will function just fine. Just stick with the Winchester. If the bolt locks up using the factory Win, do not shoot it any more and contact tech support immediately.
Ammo Warning Info |
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I cleaned the rifle and chamber again and lubed it up. I cycled 10 dummy rounds through it 3 x. The bolt and carrier locks up every 3rd or 4th round.
I don't see any unusual wear marks anywhere. The action feels good and smooth I'm suspecting the chamber also at this point. |
| Make sure you clean it out using a drill as described above. Really inspect the action and locking lugs to ensure no foreign debris is preventing rifle from locking and unlocking. Try hand cycling it using the Winchester only. I would have expected it to lock up every time rather than every 3-4 times if it was an issue with the rifle. If it still locks up, give us a call tomorrow. |
| I noticed on my new upper that the BCG was 'dragging' just before locking and stopping short. I took out the BCG and handle, generously lubed the upper, BCG and handle, then reassembled and worked the action about fifty cycles. It smoothed right out and will now close and lock even if I only pull back the handle about an inch and slowly ride it home. They must have tight tolerances or something, which is actually a good thing. When the parts wear together, it'll be smooth and tight.:) |