Does the mid length gas system make much of a difference in the 9mm carbines?
I see that ADCO mostly carries the mid length barrels. Now I love mid lengths and I’m interested in building up (or buying) a RRA 9mm but I’m not sure if I want a middy or a CAR length gas system.
Do 9mm ARs use the gas system? I thought it was blowback operated?
I have no idea, I just see Mid-Length and CAR systems offered.
I think the CAR vs. Mid is only a matter of which handguard length you prefer in 9mm ARs. Unfortunately this is like the blind leading the blind so I should probably shut up until we find a definitive answer on this 
Check out the 9mm bolt/carrier at ADCO (upper parts page). No gas key.
Yep, I just saw that!
You’re right, it looks like it boils down to rail space. However, I also saw the RRA 10.5" upper :eek:
Maybe I’ll go ahead and get the lower receiver and send off the SBR paperwork
I’m building up a 9mm as we speak.
The 9mm is blowback, not gas operated. I went with a 5.5" TROS 3 lug barrel.
I plan to put carbine length hand-guards for use with my suppressor.
I figure, if I’m going to SBR, I might as well go short 
The best prices I’ve found for a lot of the 9mm stuff is ADCO and Rainier.
Also, if you are building your upper, you don’t need a 9mm upper, but it will help with the gas blow back, especially if you are a left handed shooter. The 9mm upper has the gas block half-moon thing on it.
My build will be:
LAR Giz lower (SBR’ed lower)
RRA upper
TROS 5.5" bbl
Magpul CRT stock
probably YHM hand-guards, but I haven’t decided yet.
Chris
My Colt 9mm is blowback operated. I don’t think I’ve seen a pistol caliber AR that uses anything but blowback.
Although, I’m willing to admit there is way more stuff out there than I’ve seen, so I could be wrong. In this case, I’d say my confidence is high.
9mm is 100% blow back (no gas system). I personally like the middy"look", but it is really just personal preference.
Marc, I have the RRA middy 9mm uppers in as well.
C4
I built my RRA A4 16" with CAR handguards last April and later on when I SBR it, shorten it to 10.5".
Someone also told me that there was another way, get the middy with the gas block model, change the handguards to a middy FF rails (or longer), when converting to a SBR just remove the gas block (it won’t have any holes under the barrel like a standard FSB), shorten the barrel and use a can as an option.
If you’re going to use a can, make sure the can is compatible with the FF rails you’re going to use.
My 9mm carbine have all RRA components except the Hahn top load mag block, Colt mag, duckbill grip and an aftermarket buttstock.
C Products will be releasing their Colt clone 32 rounds mags by the end of this month, their version is a stainless steel with black teflon finish and same as Colt’s bolt hold open followers for around $30 each.
What about RRA 9mm lowers?
Can order you one of those if you like.
C4
How does the RRA mag well adaptor attach to the lower? I have been thinking about your suggestion on feeding the beast and 9MM might be in the future, but I do NOT want to take a chance on damaging my lower.
what’s a “gasblock half moon thing?”
I’m guessing the brass deflector, which for the 9mm is also supposed to deflect gases.
You tighten a screw at the bottom that locks it into place.
C4
Yeah, does the RRA 9mm lowers use an adapter? Is it forged that way or is there some sort of permanent adapter?
Two questions on that. Is it possible to over tighten and break stuff? Do you still use standard mag release lever?
Hope so, my spare 5.56 lower is a 9mm marked RRA.
IOW - They’re the same as 5.56 other than the marking.
I suggest the top loading block. “drops in” from the top, mine was really tight, they are pricey for the good ones.
I strongly suggest having the bolt ramped by Lee Minor and you need the 9mm hammer. If you don’t ramp the bolt, the hammer/trigger pins take a beating and are subject to breaking, hence the suggested ss pins. The hammer “hook” will also beat the piss out the disconnector. Cure for that-ramp the bolt and grind it(hammer) down some. If I remember correctly, once the bolt is ramped, you can keep the regular hammer.
M4arc, For info, Bob Yurina did all of my work, modified th emags, cut the barrel, installed the tros 3 lug, etc.
Simply Dynamic has the upper now and is on one of his pic threads.
My true suggestion-save the money and don’t do any of it. Unless you need a secret squirrel suppressed limited range sniper stick.
oh yeah–the set screw block is a piece of crap, doesn’t stay, will mark the lower up. I’ve seen peopl edo permanent mods to the lower to keep it locked in.
I guess, but you would have to be an idiot to do it. 
They use the standard mag release button.
C4