Optimum Barrel length, suppressor, accuracy newbie question

[daveoakley]

I'm building a 300aac ar15 that I plan to put a suppressor on it.
9" is the "optimum" barrel length. The question I have is if 6.5" and I add a 3" suppressor, for optimum ballistics, is it now a 9.5" barrel? I think the answer is "no" but someone I thought knew said "yes" since the gasses are still expanding and pushing the bullet. (that was his logic, not mine; seems to me that while gasses are expanding they've lost their "push" when they start expanding in the larger volume suppressor...
Thanks

 

[s76]

I'm going g to say no to 6.5" barrel + 3" suppressor = 9" optimal barrel. This opinion is based on no fact or scientific anything.

With shorter barrels the bigger question would be is the suppressor rated to/able to handle the muzzle pressure?

I have a 7" 1:7 twist SS barrel with a 7.5" suppressor and its plenty accurate. I can get factory 110gr ammo to ~2300 fps.

 

[Theohazard]

A typical rifle silencer might give you 10 - 30 extra FPS in velocity if you’re lucky. But it might not. The equivalent length in extra barrel length will reliably give you a lot more than that, usually a few hundred FPS. But it’s different depending on the loading: 5.56 is very dependent on barrel length, 300 BLK supers are less so. And subsonic 300 BLK is not very dependent on barrel length at all.

9” is considered the optimal barrel length for 300 BLK because it’s the shortest length that still gives good performance with supersonic ammo. And a very short barrel is great for silencer use. But if you want better performance with supersonic ammo, go longer.

 

[daveoakley]

Thanks. I am after compact home protection. So I was hopeful that 6" barrel + 3" suppressor = 9" barrel so I could use supersonic ammo with reliability tool.

 

[Theohazard]

Thanks. I am after compact home protection. So I was hopeful that 6" barrel + 3" suppressor = 9" barrel so I could use supersonic ammo with reliability tool.

You’d have a hard time finding a 3” silencer that will handle 300 BLK supers, anyway. You’d most likely have to make your own. But a silencer that short wouldn’t do much more than lower the muzzle blast; it would be a little quieter, but still really loud.

 

[Varminterror]

Just so much wrong with the entire premise. 9” isn’t any kind of “optimum” worth pursuing in 300blk, a 3” suppressor would be worthless on a 300blk - especially a 6.5-9” 300, and suppressors don’t really replace barrel length in the way you’re proposing, damned sure not a inch-for-inch replacement, especially not on a short barrel, and especially not a wastefully short 3” suppressor. I’d rather have a 9” barrel with a linear compensator (which are constructed the same as a single baffle suppressor) than waste time, energy, and money on a 3” suppressor for a 300 blk.