.300 Blackout Velocity by Barrel Length
Velocity by barrel length for .300 Blackout (also known as ".300 BLK" (SAAMI) or ".300 AAC Blackout" (C.I.P.) - From MrGunsnGear on YouTube. We'll also briefly discuss best barrel length for something like an AR-15 pistol, below to allow you to better navigate various typical barrel length offerings.
|Barrel Length||110 gr. (Velocity)||110 gr. (Energy)||125 gr. (Velocity)||125 gr. (Energy)||150 gr. (Velocity)||150 gr. (Energy)||220 gr. (Velocity)||220 gr. (Energy)|
|16"||2412 fps||1421 ft lbs||2221 fps||1339 ft lbs||1854 fps||1154 ft lbs||1102 fps||593 ft lbs|
|12.5"||2289 fps||1280 ft lbs||2118 fps||1245 ft lbs||1789 fps||1066 ft lbs||1027 fps||515 ft lbs|
|10.3"||2203 fps||1185 ft lbs||1984 fps||1094 ft lbs||1709 fps||973 ft lbs||960 fps||450 ft lbs|
|9"||2167 fps||1147 ft lbs||1975 fps||1090 ft lbs||1661 fps||919 ft lbs||957 fps||447 ft lbs|
|7.5"||2118 fps||1096 ft lbs||1957 fps||1063 ft lbs||1709 fps||973 ft lbs||953 fps||444 ft lbs|
Best Barrel Length For .300 Blackout
For Subsonic Loads
Based on the data above, it appears that for subsonic loads such as 220 grain (where the .300 BLK really shines), barrel length can be an afterthought, particularly if you plan on using a suppressor. Something like a 7.5" barrel with an appropriate 7 to 8 inch suppressor would allow for a package that is still shorter and a little handier than a typical 16" barrel setup. Keep in mind that many manufacturers will not warranty their suppressors on barrels shorter than around 7.5 inches. This would still make a handy setup for military and law enforcement applications, as well as home defense or just a fun recreational setup for novelty.
For Maximum Velocity
If one were so inclined to use their .300 AAC Blackout setup as a full barrel length "AK replacement" in an AR-15 platform and without a suppressor, a 16" barrel will of course give you the most velocity out of any load, and more energy out of subsonic loads as well. Of course, adding a suppressor to that setup would give you a functional barrel length of over 22", which is not particularly handy. This could be acceptable for 5.56 but not as justifiable in a shorter range .300 Blackout rifle. Also, with the added length of the suppressor, some subsonic loads might break the sound barrier, so this is also something to consider beforehand.
Best Overall Barrel Length for .300 Blackout
The major question still comes down to whether you plan on using a silencer or not. If strictly looking for quietest and best handling setup, one could easily go as short as 5.5" which is offered by a number of manufacturers. Remember, a 7 to 8 inch suppressor will add velocity and make up for such a short barrel, but not fully. Overall a good compromise would be a barrel in the 7" to 9" range, which will offer an overall barrel length of about 14 to 16", granting solid muzzle velocity with all loads, handling that is slightly better or similar to a typical 16" carbine setup, and has the benefit of having a suppressor attached. 7.5" would probably be your best bet overall with a suppressor, especially since this is the minimum warranty barrel length for most suppressor manufacturers. If you want maximum velocity with a barrel still shorter than the norm and don't plan on using a suppressor, 12.5" is a great choice for a pistol style setup. And even if you opted to add one, you're still around (or just under) 20 inch barrel length, which isn't terribly excessive. Another thing to note is that shorter and thicker suppressors are out there, such as the Brevis II line from Delta P (5.5 inches long). This would allow a 12.5" barrel to make much more sense, but suppressors like that are not cheap.