I have a 9mm factory SBR Rock River Arms AR15 that runs like a champ. I’ve removed the flash hider so that I could thread my TiRant 9 suppressor on. I then got to thinking that I need to install a heavier buffer. Then I got to thinking more and realized that the rifle is straight blowback and there is no gas system, so I don’t need to change the buffer. Then I got to thinking even more and remembered that I sometimes have to change to lighter recoil springs when shooting my suppressor on my handguns. Finally, I decided that it would be best to simply ask. So do I need to change to a heavier or lighter buffer when running a suppressor on a 9mm AR15?
Straight blowback is a form of gas system acting directly on the case.
The suppressor will increase gas impulse slightly, but probably not enough to worry about if the buffer is already heavy enough.
The RRA 9mm ships with a Colt style 5.5oz buffer
Oops…double tap
Good to know. I’ll run it with and without the suppressor to see if there’s a difference in the ejection distance.
Though I don’t know about the weight, they do not look the same. The RRA is on the left and the one from my Colt SBR is on the right.
The RRA has a roll pin through it that allows the rear of the buffer assembly to slide front to rear relative to the rest of the buffer assembly.
I can’t figure out what the thought is behind the different design.
Here are some good threads that discuss the issues around 9mm buffers.
Short version of the hot setup: Longer & heavier buffer with stronger action spring.
https://www.m4carbine.net/showthread.php?177737-MAKING-A-9MM-BUFFER-SPACER-MAY-HAVE-EXTRAS
https://www.m4carbine.net/showthread.php?148118-9mm-buffer-spring-questions
https://www.m4carbine.net/showthread.php?176895-Buffer-options-for-Colt-9mm
I read through most of the threads. They seem to discuss how to setup a 9mm, but are not oriented around taking a well functioning 9mm and getting it to run with a suppressor. Given that my RRA is running reliably, do you agree with hk_shootr that I’ll probably be ok leaving things as is? Or, is it your experience that most of the time the spring or buffer needs to be changed when running a suppressor on a 9mm AR15?
Proper setup with a heavy buffer should allow function either way.
Go ahead and try what you have now, but don’t be surprised to have similar experience as below:
https://www.m4carbine.net/showthread.php?192227-Reduce-ejection-port-noise-suppressed-9mm-ar
https://www.m4carbine.net/showthread.php?194489-PDW-stocks-9mm-and-you
https://www.m4carbine.net/showthread.php?87364-Suppressed-9mm-AR
Give Rudy a call and Macon Armory and ask him………he usually answers the phone and more than happy to answer your questions………I consider him a Guru when it comes to PCC………
Interesting. My 9mm Colt carbine that I bought new about 15 years ago has a buffer that looks exactly like the RRA you pictured. Is your Colt a newer model? Searching Colt 9mm buffers show the design to be just like I have.
I would suspect Macon Armory will recommend changing to a buffer that weighs 8-12oz
You might think about getting a buffer tube spacer for your RRA as well.
That’s interesting. I bought the Colt SBR about a year ago.
I bought the Colt 9mm SBR right at a year ago. I just checked the buffer that came in a Tiger Stripe finished Colt 9mm receiver set that I bought last June. It’s the same.
Running multiple AR-9 setups suppressed… I would go with a dedicated 9mm 7.5-8 oz buffer and 308 spring. With your current setup I would still put in a 308 buffer spring and $1.50 in quarters to act as a buffer stop in the buffer tube… your going to need it !
I shot my RRA 9mm SBR today. I started with 100rds of Speer Lawman 147gr TMJ. It ejected about 10 feet to my right with and without the suppressor. There was definitely not a noticeable difference in the ejection distance. I then attempted to shoot some CCI Blaser aluminum case 147gr FMJ. The rifle would fire, but would not eject the spent cases. They’d just end up getting smashed by the bolt right outside of the chamber. After five failures in a row, I gave up on this ammunition in this rifle. Just for a sanity check, I put 25rds more of the Speer Lawman 147gr TMJ through the rifle. It again functioned 100%. Given the short ejection distance, I think that I’m going to leave well enough alone. Thanks everyone for your help. Perhaps I was just overthinking things.
Every thing Ive ever read about aluminum case ammo in blow back carbines is to stay away from using it………I have no experience in either of my AR 9’s and with that said, I have seen numerous posts about not using aluminum case ammo and problems associated with it…
Well then I can confirm what you read.