With Grant having such a great price on Colt 6450s I am considering getting one but plan on SBRing it.
I don’t want to go too short since I may as well have a pistol at that point. However I want it to be maneuverable in close confines. It will also probably wear a can quite often.
I have been looking for the same info and found this thread.
I went with 8" for my 9mm AR pistol and am very happy. The best barrel I could find was from Bravo Co. (10" chrome lined). I had to have it cut back and threaded. I can group three rounds at 1" at 50 yards from a bipod. That length is towards the top of the curve shown in the DDLES generated curve. I also chose that length because it got the threaded end of my comp (soon to be suppressor) just inside a 7" quad rail. The MP5’s are about that length but they are ported to stay subsonic? I will have the use 147+ grain to do that but can also enjoy the higher velocity +p loads non-suppressed. I will try and get some actual velocities with different loads but don’t have access to a chronograph at this time.
Two thoughts to consider iif running suppressed:
A 5" bbl will be subsonic with most if not all loads; 7+ inches will require 147gr or subsonic loads to remain subsonic.
A 5" bbl plus a 6-8" suppressor = 11-13" overall bbl length; an 8" bbl plus suppressor isn’t going to be longer than a “standard” M4 clone (unsuppressed, of course).
Nice. Thanks for sharing.
Great info, thanks guys! I’ll be sbring my 6450 soon also. I’m waiting on the flat top upper and the Aimpoint.
IIRC mine a 5" adco… Ron
I went 5.5" on my 9MM AR-SBR, it always has a Tirant 45 on it as well.
Velocity gains drop of substantially after 6" from my research.
I’m not so sure about this. 9mm ammo velocity numbers are typically based on 4-5" test barrels since the ammo is designed for pistols. 115gr ammo will be supersonic even from most if not all 3" barrels.