Question about fps x39

[Rebel_Rider1969]

Talked to a guy awhile back about brown bear sub-sonic ammo. He told me out of the 16 inch ak it was sub-sonic, changed to an AR15 with 10.5 barrel it would crack, and break the sound barrier. Dont know if he chronoed the ammo, but how could it do this?? Is the AR that much more effective?

 

[FamilyFirst]

KY jelly in the barrel

 

[FrommerStop]

Talked to a guy awhile back about brown bear sub-sonic ammo. He told me out of the 16 inch ak it was sub-sonic, changed to an AR15 with 10.5 barrel it would crack, and break the sound barrier. Dont know if he chronoed the ammo, but how could it do this?? Is the AR that much more effective?

Maybe the over gassed system of the AK for that subsonic loading might make the difference. I am just plain guessing here. That is the only explanation I can think of.

 

[Little Jack]

Maybe he's wrong.

5.5" less barrel is less velocity imparted on the round. Not going to go faster. Was he shooting 5.45x39 in a 47?

It may sound different out of an AK and an AR but the physics don't add up.

If true, I'd like to hear why.

 

[Rebel_Rider1969]

I was thinking the same thing. Maybe he perceived it to be louder due to the short barrel.

 

[FrommerStop]

Maybe he's wrong.

5.5" less barrel is less velocity imparted on the round. Not going to go faster. Was he shooting 5.45x39 in a 47?

It may sound different out of an AK and an AR but the physics don't add up.

If true, I'd like to hear why.

From the OP: "about brown bear sub-sonic ammo. "
He was shooting subsonic loads that are sold in 7.62x39, but not 5.45x39
There is also a 9x39 subsonic load available. A tighter chamber in the AR along with not being over gassed could make make a difference of 75 fps. Some real light fast burning powder loads may not accelerate much anyway after say 10 inches.

Brown Bear 7.62x39 196-Grain Subsonic Ammunition, 20-Round Box

$14.99
$11.99

 

[Little Jack]

5.45 in a 7.62 AK was being facetious. Lighten up Francis.