9mm SBR Barrel Length To Stay Subsonic

F-Stop · Mar 8, 2017

Hello,

I was considering doing a 9mm SBR but, I am not sure if a minimum 10.5 barrel will keep 147gr bullets subsonic. Those with experience, can you please help? I would like to stick with 147's but, if you have experience with heavier, please chime in.

If its going to be tough, I may change a existing SBR lower into 9mm and get a new 556 one that's 11.5."

Thanks!

dontpanic · Mar 8, 2017

Your load has to start out subsonic. Most if not all 147gr 9mm is. I have never seen 147gr that is not.

You will not get any appreciable increase in velocity after the first 5" of barrel length.

Check out this chart.

http://www.ballisticsbytheinch.com/9luger.html

F-Stop · Mar 8, 2017

Thank you. That helps.

IMBLITZVT · Mar 8, 2017

F-Stop said:
Hello,

I was considering doing a 9mm SBR but, I am not sure if a minimum 10.5 barrel will keep 147gr bullets subsonic. ...!

I have to ask... what SBR? If an AR... why not just put on a shorter barrel?

outrider58 · Mar 8, 2017

IMBLITZVT said:
I have to ask... what SBR? If an AR... why not just put on a shorter barrel?

29" OAL requirement in MD.

I have an AR pistol that I'm planning on SBRing in the future, but til I leave Md (for good), I will keep it a pistol with a 5"bbl and suppressor. I want to keep it short and light.

IMBLITZVT · Mar 8, 2017

outrider58 said:
29" OAL requirement in MD.

I have an AR pistol that I'm planning on SBRing in the future, but til I leave Md (for good), I will keep it a pistol with a 5"bbl and suppressor. I want to keep it short and light.

ahhh... see I always forget that one having a registered M16... I am so glad I don't have to worry about that BS.

F-Stop · Mar 8, 2017

I thought 10.5" was the starting point to meet 29" length requirement.

I may use an existing sbr lower but, was curious if I did a new one for 9mm if it would stay subsonic as I'd want to use a can under guard.

Drmsparks · Mar 8, 2017

I've read in earlier posts that 7" was the long limit to keep most loads subsonic. Good to see that information was for loads lighter than 147. Mental note, order some 147's.....

Hawkeye · Mar 8, 2017

F-Stop said:
I thought 10.5" was the starting point to meet 29" length requirement.

10.5" is the easiest one to use if you want to hit it without running a permanent muzzle device.

You can get 29" with an 8.5" barrel with NO permanent muzzle device IF you run a VLTOR A5 7 position buffer tube and a Magpul ACS or ACS-L stock *with* the 3/4" extended buttpad.

F-Stop · Mar 8, 2017

Thanks for that info. I appreciate it. That sounds like a good compromise and just leave the other builds as is. I tried the multiple uppers thing and they always end up with their own lower.

Sticky · Mar 8, 2017

dontpanic said:
Your load has to start out subsonic. Most if not all 147gr 9mm is. I have never seen 147gr that is not.

You will not get any appreciable increase in velocity after the first 5" of barrel length.

Check out this chart.

http://www.ballisticsbytheinch.com/9luger.html

That's a great resource, thanks!

ashershapiro · Mar 9, 2017

I have a 10.5 inch 9mm. My 147s stay subsonic for the most part. I did shoot it out in the cold for the first time this winter and a couple of rounds went supersonic. So you're gonna be right on the border. Spring and summer time weather , I never had an issue.

rayrevolver · Mar 10, 2017

The new interest in Pistol Caliber Carbines (PCC) is why the generation of 9mm 158gr subs sell out (Fiochi or PPU).

Most report they are quieter as well. I have a case of the PPU 158, AE147, and Speer 147. Plan on doing my own test to see if the 158s are worth the extra cost, but probably not with my 5.5" barrel.

9mm SBR Barrel Length To Stay Subsonic

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