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Posted: 2/25/2007 8:11:40 PM EDT
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Hi folks, Really thinking about building a 9mm AR but I'm just getting myself more and more confused as I am reading the FAQ and the rest of the threads. I have a KAC midlength FF currently and would like to eventually see a setup like the suppressed SWR 9mm upper. I'd probably start with a stripped RRA 9mm lower and build up from there after the appropriate NFA forms are filled out. So, I have a few questions for all that know more than me as this would be my first 9mm build. 1. I'd like to use the new CProducts mags when they come out, as well as Colt mags. I'd also like to have a bolt hold open feature--so, which conversion block should I get again? Does the AR mag release actuate the mechanism for 9mm mags to drop? Would a ambi-AR mag release work? 2. Planning on getting the RRA 9mm hammer and the rest of the lower parts kit. I was looking at the RRA website and saw a "9mm stock spacer"--what's this for? I thought all that was needed was the carbine spring and 9mm buffer. 3. As far as an upper receiver goes, is it just a standard AR upper with a different type of dust cover? Feedramps or no feedramps? 4. During upper assembly, does the barrel assemble the same way as an AR barrel? 5. Since 9mm are basically blow-back, there's no gas tube or anything forward of the upper receiver except for if I want an FSB? Thanks for all the help in this matter. I appreciate any advise! |
1. I think you are going to want the Hahn dedicated block as you will besically be leaving it in the lower forever. It requires removal of the bolt catch to install it and it should activate a standard bolt catch so you don't need a colt-style extended bolt catch. 2. RRA sells a 9mm stock spacer to allow you to use a 9m carbine buffer in an A2 length stock/buffer tube. If you were going with an A2 stock and buffer tube, just skip the 9mm buffer and run an A2 buffer as they are the same weight. I make a short spacer that takes up the excessive buffer travel in both systems and protects against broken bolt catches due to excesssive bolt overtravel. 3. You CAN use regular upper receivers with the different ejection port cover and brass deflector installed, but 9mm uppers are unique in that they will NOT have a forward assist on them. If you use a regular receiver, that feature is not available. NO feedramps in the upper receiver, the mag block has the feedramp. 4. Yes, but there is no gas tube so alignment of the barrel nut is not quite as critical. 5. Correct. I have carbine and mid-length RRA 9mm uppers in stock if you need one. I can install any handguard system on it and shorten to any barrel length and thread the muzzle to any thread spec while I have it all apart... |
Thanks, Randall! I'll have to get the lower and SBR it first--but I may take you up on that offer!! As for the RRA factory block, what's the difference between that and the Hahn block? And is there such thing as a chrome-lined 9mm barrel? |
I have not held a Hahn block, but from the pictures, they have a little piece in them that trips a regular 5.56 bolt catch where the RRA block needs you to use an extended 9mm bolt catch. Just so you know, you will need Colt mags to actuate any of these. The new C products mags will hopefully have the rib down the back and a proper follower as well. M60 Joe also modifies Uzi mags by welding a little spring steel tab on the back of the follower and making a slot for it to pop out at the top kinda like old style AR-10 mags. Only Colt has produced a chrome lined 9mm barrel. It's just not necessary in 9mm... |
Thanks!! More than helpful, once again, Randall!! Now to start gathering . . .  Another question--what's this with ramping a 9mm carrier? Is this recommended if I have a 9mm hammer? Who does this type of service? Thanks again!! |
The ramping reduces the forces on the hammer when the bolt first starts moving rearward. Search on "ramped" and "ramping" and read about it more thouroughly. You can ramp TOO MUCH and then the 9mm hammer will not work. When you are reading all the ramping threads, you will run into the people that are doing this work as well. I recommend KNS 2nd generation pins be used on 9mm lowers to give you a SOLID pin with no groove in it. This will eliminate any breakage of hammer pins that is attributed to non-ramped 9mm bolts. |
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