Subsonic with 10.5 9mm AR

IgotAgun · Feb 28, 2015

I'm currently building a suppressed 9mm SBR. Because of the laws I'm going with a 10.5 inch barrel. I'd prefer a 5 inch barrel, but oh well. Do factory 147gr stay subsonic most of the time? I reload 9mm, but I like to supplement with factory ammo from time to time.

mtlcafan79 · Feb 28, 2015

http://www.ballisticsbytheinch.com/9luger.html

IgotAgun · Feb 28, 2015

Thanks. It looks like I'm right on the border when its very cold outside at least.

dontpanic · Mar 1, 2015

With 9mm you get almost no increse in velocity after the first 5 inches. If you load your own then check your manuals, there are a lot of options for subsonic 9mm.

I'm new to reloading, but I'm working on a 124gr subsonic round for my 10.5" AR. I'm also thinking about using lighter bullets.

Pinecone · Mar 1, 2015

Why would you use lighter?

With subsonic, you are limited in velocity by the speed of sound. To to increase energy/momentum, you need to go HEAVIER for the bullet.

One uses light bullets in a firearm to increase the velocity. And since the energy is based on velocity squared, the energy goes up faster with increased velocity, than it goes down with decreased bullet weight.

So going from 147 gr to 124 gr (at the same velocity) you lose 16% of your muzzle energy

Sundazes · Mar 1, 2015

Pinecone said:
Why would you use lighter?

With subsonic, you are limited in velocity by the speed of sound. To to increase energy/momentum, you need to go HEAVIER for the bullet.

One uses light bullets in a firearm to increase the velocity. And since the energy is based on velocity squared, the energy goes up faster with increased velocity, than it goes down with decreased bullet weight.

So going from 147 gr to 124 gr (at the same velocity) you lose 16% of your muzzle energy

I thought it was 3% :innocent0

ericoak · Mar 1, 2015

dontpanic said:
With 9mm you get almost no increse in velocity after the first 5 inches. If you load your own then check your manuals, there are a lot of options for subsonic 9mm.

I'm new to reloading, but I'm working on a 124gr subsonic round for my 10.5" AR. I'm also thinking about using lighter bullets.

I don't know about that. There is a reason body armor ratings account for 9mm out of a pistol and 9mm out of a subgun. That extra length can add 150-200fps. I don't think you would want to get shot in a 9mm handgun rated vest (Level II) with a long submachine gun length barrel (would want a Level III-A).

dontpanic · Mar 1, 2015

Pinecone said:
Why would you use lighter?

With subsonic, you are limited in velocity by the speed of sound. To to increase energy/momentum, you need to go HEAVIER for the bullet.

One uses light bullets in a firearm to increase the velocity. And since the energy is based on velocity squared, the energy goes up faster with increased velocity, than it goes down with decreased bullet weight.

So going from 147 gr to 124 gr (at the same velocity) you lose 16% of your muzzle energy

Go lighter because 124gr costs less. There is a lot of load data for subsonic 124gr 9mm. You also use less powder.

I am mostly going to load for plinking so I can only kill paper so much.

http://www.hodgdonreloading.com/data/pistol

BTW: Not trying to be preachy on this. I am trying to learn more about this as well.

Subsonic with 10.5 9mm AR

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