Suppressors and velocity/energy

[Rikakiah]

I have a 16" M4 (DDv7). My original plan was to get a ~10" .300BLK upper to fulfill my dream of a suppressed SBR. However, financially, that's a little farther down the road than anticipated. So, in the mean time, I'm planning to trim my 5.56 barrel down (and run it with the same suppressor). Upon initial thought, I'm wanting to do this even if I managed to get a .300BLK tomorrow, since the more I think about it, the more unwieldy a suppressor can be at the end of a 16" barrel.

I already know this setup should add at least much of the pressure back that I would lose from the shorter barrel, giving me the needed dwell time that the DD mid-length prefers.

However, how does a suppressor affect ballistics? I'll probably be cutting about 4+ inches off (rough measurements put the gas block about 5 inches from the end of the barrel, so figure maybe 4.5" is my max cut) as I want the attached end of the suppressor to reside decently within the rails/handguard (purely aesthetics, but really doesn't affect the concept). The ballistics out of a 11-12" barrel that I've seen for 5.56 are decidedly weaker than expected.

SO, my question is, will the suppressor add back the lost velocity (and as a result, energy), or does it simply add back pressure and the bullet won't receive any noticeable benefit? If it does, is it similar to an actual barrel (ie a 10" barrel with 6" suppressor has virtually identical performance to a 16" barrel) or is there something lost or gained in translation?

[Willie Lowman]

However, how does a suppressor affect ballistics?

It does not. They can affect point of impact.

will the suppressor add back the lost velocity

Nope.

[Rikakiah]

Well phooey. I'm still cutting it...in 6-12 months when I finally take my suppressor home.

[allaroundhunter]

It actually does add some velocity back. It is similar to a barrel in that it is still an extended length in which the gases are propelling the bullet rather than dispersing. However, it will not give you equal velocity to the barrel length before you cut it.

[Theohazard]

Originally Posted by Rikakiah

will the suppressor add back the lost velocity

No. You're going to lose about 200 - 400 FPS with the cut-down barrel. A suppressor might increase the velocity by 10 - 30 FPS (it's called "suppressor boost"), but it might not increase it at all.

Originally Posted by allaroundhunter

It is similar to a barrel in that it is still an extended length in which the gases are propelling the bullet rather than dispersing.

That's not entirely accurate. A barrel increases velocity linearly and predictably (up to a point), and it works basically the same way in every barrel. But suppressor boost is complicated, controversial, and inconsistent; not at all like the velocity increase you get from a longer barrel. Also, when it does happen it's by a very small amount: The most boost I've heard someone claim was 50 FPS in a .223, and that's rare. Usually it's closer to 10 FPS.

I've never heard a good explanation of why suppressors sometimes boost the velocity a tiny bit and sometimes don't. But most people seem to agree it doesn't work quite the same way that a longer barrel does.

[Deja vu]

I found that my 22lr suppressor did not change point of impact or change velocity.

I found that my 45-70 suppressor added a very slight amount of speed. Hot loaded ammo gains about 20 fps, sub sonic ammo gained little to nothing.

no where near what even 2 extra inches of barrel would add.