Does anyone know what the optimal barrel length is for 9mm rounds for max velocity?
Say, standard 115gr FMJ rounds for start.
I know different loads could change optimal barrel length but anyone have a ballpark?
I was just wondering if it was in SBR range or if the 16" was getting close.
Thanks in advance.
I thought I read somewhere that 10.5" was optimum for 9mm ?
I may be wrong though…
Hard to get a deffinitive answer on that. Many people base it on what companies do such as an MP-5 is in the 8" range I think.
I just searched and searched and can’t find a good site with velocity specs to compare. Lots of charts out there but they’re all different loads with different barrel lengths.
One site quoted a PMC test done on penetration not velocity. It said something to the effect that extremely short barrels that don’t produce enough velocity will penetrate further because the bullet won’t expand.
Another chart I saw was purely built off theoretical numbers. Velocity was graphed rising all the way to the end of the chart at 16". The criticism it brought on was that at some point the length of the barrel causes friction and it should drop off.
I guess until someone chrono’s the same ammo from 16" and cuts/re-crowns an inch at a time, we’ll never know.
I have a 9.25" TOS barrel on one of my SBR’s and It’s every bit as accurate out to 25yards as the 16" guns. I can shoot it out to 75 yards easily hitting a 12x12 steel plate.
I don’t know about velocities in the 9.25" barrel, but the 16" barrels I chronoed a while back were only running 100 to 150 fps faster.
WWB VP was averaging 1269,
Ranger 127+P+ was 1401,
Golden Saber 124+p was 1277,
Speer 124 +P was 1418 (and the most consistiant),
Federal Hydra Shok 124gr was 1207,
Mag tech 115gr was 1237.
I keep a mag of Ranger 127+P+ loaded, not that I’d grab the 9mm AR for defence, But It’s nice to have a mag ready 
I tested this a couple of years ago with a 5", 10.5", and 16" barrel.
Ammunition used was the same, though I can’t remember if it WWB or Magtech.
I’ll have to search my PC for the results, but if I remember correctly statistically there was little difference between the 10.5" or 16" barrel. While I did not measure accuracy to the fractional inch. Both barrels where equally accurate out to 100 yards from the bench with iron sights.
Will subsonic 147gr. stay subsonic out of a 10.5" 9mm barrel if it is out of a pistol barrel?
Sorry to dredge up an old thread, but my search didn’t yield the results I was looking for…
I’m looking for an answer to this question as well.
To be more specific, what is the best length for a barrel while still keeping the bullet subsonic? I’m trying to decide on whether to get a 5" or 7" threaded barrel from Spikes and plan on shooting 147gr. Federal HST out of my SBR. My concern is that the 7" barrel may be enough for the round to go supersonic. Am I justified or is it a non-issue?
I’d like to have the extra two inches if it might eke out a couple hundred more fps, but won’t if it’ll mean losing out on the effectiveness of the Ti-RANT.
Try this site:
http://www.ballisticsbytheinch.com/9mmluger.html
Looks to me like 12 inches is where the curve flattens out for most types of 9mm ammo.
A 3 to 4 inch barrel is the sweet spot for real subsonic, not transonic where you still get an increase in sound signature. Our 4 inch barrel still keeps factory 147’s subsonic. A 5 inch barrel is too long to keep a good subsonic sound signature.
Thanks Jon!
147gr HST stays subsonic out of my 5" TROS.
One of my favorite SD loads for my AR9mm is 147gr XTP over 6.5gr of 3N38 for 1,180fps from my 5" TROS!
1,180fps is transonic. You will notice a significant drop in sound signature when you are around 950fps.
http://en.wikipedia.org/wiki/Transonic
“Transonic is an aeronautics term referring to the condition in which a range of velocities of airflow exist surrounding and flowing past an air vehicle or an airfoil. Air flow velocities are concurrently below, at, and above the speed of sound at the pressure and temperature of the airflow of the air vehicle’s local environment (about mach 0.8–1.2). It is formally defined as the range of speeds between the critical mach number, when some parts of the airflow over an air vehicle or air foil are supersonic, and a higher speed, typically near Mach 1.2, when all of the airflow is supersonic. Between these speeds some of the airflow is supersonic, and some is not.”
Yes I knew that, sorry I wasn’t clear but I wasn’t saying that particular load was subsonic or quiet cause it’s far from it…it makes a nice SD load though 
I do try to keep my Subsonic loads around 950fps.
Gotcha, sorry about that.
Interesting chart DDLES. Looks like no real velocity benefit to barrels longer than about 5" with that particular load, and as you said after about 4" there may be louder sound.
You said you’re doing 4" barrels? Is that a 4" threaded barrel? I have a YHM 9mm can that mounts to a flash hider.
Yep, threaded 1/2X28
I had no problem keeping reloads subsonic out of my colt 10.5" upper.
Reloading is the way to go. 147gr. rainier bullets and iirc, 4.3 grains of red dot…
If you reload with a slow burning powder like HS-6 or Power Pistol, you can get a 115 grainer up in the 1500 + fps range for 75-100 yard shots.
With quality 115 or 124 grain ammo, you should get a 16" barrel.
Find some GECO or MFS South African 115 grain ammo - nice and hot and will shot long accurately.
If you use PMC or some other crappy ammo, you should still be getting another 75-100 fps with the longer barrel.
45ACP does not accelerate much after 10.5". That is why 45ACP is best suited for AR-15 pistols - 9-10" barrels. Having ADCO cut mine down soon:D
I fire a lot of suppressed 9mm - been making my own ammo for quite a while now - 147gr and 4.8gr Unique powder. More or less tailored for me to works well suppressed barrels up to 10.5"
I had read that the Uzi was built around the 10" barrel because anything longer than that, the bullet actually started slowing down…looking at the cart that doesn’t seem to be the case.