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Posted: 6/29/2011 4:37:25 PM EDT
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Hoping someone here might have a clue....
I'm having some issues with my 9mm MRP conversion. The MRP is using a Spikes barrel, CMMG 9mm BCG, BCM charging handle, factory RRA 9mm lower. Everything is put together correctly (barrel/upper). At first I thought it might have been the ammo I was using (BVAC). I tried some new ammo today and figured out what was really going on. Upon inserting the magazine (metalform), chambering the first round, and firing...the rifle deadlines. The BCG locks back about 3/8 of an inch. I have to give a firm muzzle smack to get the BCG forward, separate the lower and upper, manually reset the hammer and pull out the fired brass. What I noticed today was the hammer wasn't being reset by the BCG. I can rack the carrier all day long with the hammer down, but once it's up, it's frozen. I have to separate the rifle and manually reset the hammer. I can replicate this by doing a function check too. Once that hammer is forward, it stays that way until I manually reset it. Let me know if you need pictures of anything. ETA: 
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I found this in the archives from CMMG themselves:
" 'So will this work with the 9mm hammer or just the .223 hammer?' These only work with standard hammers." http://beta.ar15.com/archive/topic.html?b=3&f=124&t=416421 Further down in that thread it is stated that a 9mm hammer will not work with a CMMG ramped bolt. Sounds like a relatively cheap way to troubleshoot your problem would be to drop a standard rounded .223\5.56 hammer in there and see if it works.  FWIW, I run a CMMG BCG with the rounded hammer and have flawless function
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Hope it solves your problem! Let us know.
Eta: one thing I kept coming up on while researching my build was 9mm guys always using KNS anti-roll pins to help mitigate the brutal cycling of that heavy bolt and the damage it CAN cause to those pin holes in the receiver. They're unbelievably easy to install without un-assing the trigger group from the lower if you ever decide to pick up a set. |
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