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11/20/2019 5:07:11 PM
Posted: 11/2/2009 4:47:04 AM EST
Hey guys,

I'm running a brand new RRA 10.5" 9mm upper with the notched single stage RRA FCG and a RRA 9mm bolt that has been ramped by ADCO––lower is a dedicated CMMG 9mm. I can not close the upper on the lower when the hammer is in the forward resting position as it appears that the bolt is making contact with the leading edge of the hammer-is this normal? If I cock the hammer first the upper and lower go together just fine and the weapon cycles just fine. The hammer is the small notch 5.56mm RRA single stage. TIA!!!!!
Link Posted: 11/2/2009 1:30:37 PM EST
I have a very similar setup but I got use to sliding the upper sort of down and back and I guess that is pushing the hammer back a bit to let the upper seat. Maybe someone else has more knowledge of these things but if it is working OK I wouldn't worry about it. You do have a different bolt in the 9 than you do a standard rifle.d
Link Posted: 11/2/2009 3:56:17 PM EST
I have 71/2" RRA upper, lower, mag block and bolt ramped by Adco, all lower parts RRA except hammer is M16 with hook removed, same as a DPMS. Hammer clears bolt, but more important clears rear of firing pin? I know the 9mm guys out there will know
Link Posted: 11/3/2009 3:44:34 AM EST
Alright guys,

further inspection appears to show that the notch of the hammer is getting hung up on the rear face of the firing pin when trying to close the upper onto the lower without the hammer being cocked.

Also,when trying to perform a function check I find that if I hold the trigger fully to the rear and charge the weapon, the hammer IS NOT getting cocked. The lower alone without the upper attached passes all function checks.

At this point I'm thinking that maybe it's a hammer related problem and I should probably switch to a DPMS hammer? Anyone know where I can find a DPMS hammer these days? Also, I did have Bill Sprinfield do an excellent trigger job on my FCG––how will replacing the hammer with a new DPMS effect this, will I need to get the trigger job redone? TIA!!!!
Link Posted: 11/3/2009 4:35:48 AM EST
It is common, even normal to have problems closing ANY AR with the hammer at rest. You may also find that the rear lug of the RRA upper is pretty tight. That's a good thing, by the way.

I'd spend about $15 and buy a DPMS hammer for that lower though. Notched hammers are a problem in a lot of applications. A DPMS hammer (which looks like an M16 hammer with the rear hook removed) will work with every upper there is, while a notched hammer is problematic with many .22 adapters,and questionable with some 9mm bolts. The notch is supposed to keep the hammer from "following the bolt and firing," but the genius that invented the notch was basing it more on theory than real experience. Dump the notched hammer and you'll be happier.
Link Posted: 11/3/2009 4:54:12 AM EST
thanks guys,

I just ordered a DPMS hammer to try!!! Another question–– is the safety function check the same for a single stage trigger as it is for a 2 stage? This is the first single stage that I've run, all my other AR's have a 2 stage in them.

With the trigger held all the way to the rear, and after charging the weapon, I should hear a "click" if I release the trigger a little then the hammer should release if I pull the trigger all the way to the rear ––correct?
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