I don’t know how you call the different MP5 SMGs.
You have the regular one (with no intergral silencer) and the special one (with an integral silencer).
With the first one you must use subsonic rounds when you attach a sound suppressor.
The optimum will be : the heaviest bullet going just below the sound velocity.
it gives : 158 grains, 1000 fps
about the second one. (you must call it SD I think).
This gun, like the silenced Sten, like the 22 High standard, like the 32 ACP Welrod, aso, use standard ctges (supersonic).
(125 grains bullets for example)
In order to get a sub sonic velocity at the exit, they drill holes into the barrel (ported barrel)
Pressure is therefore decreasing, and velocity also.
At the exit the bullet is going just below the sound velocity.
Therefore we have : 125 grains, 1000 fps.
If we compare the two momentum we see : 33 grains difference, same velocity
it makes a 26 % increase in momentum for the first one !
The ported barrel silenced guns have other problems :
if the gun was designed to reduce the speed with one kind of ammo, and if you use another kind of ctges having a lower velocity (in a standard barrel), of course you will have a lower velocity at the exit.
And you can be at 800 fps for example (the decreasing in velocity is not proportionnal to the velocity of the ctges tested in a standard barrel)
The momentum is decreasing a lot !
- the accuracy is not as good (because of the holes)
- to clean the integral silencer is a lot more difficult
The ported barrel silencers are old designs and show lack of efficiency on a live target.
They are very silent because the velocity of the bullet is often very very low.
(For US readers, all the suppressed weapons of Jonathan Ciener were like that.He stopped to manufacture silencers because of liability, paperwork and so on, but also because there was no way to compete against the new silencers (which are chemical).
- Even 147 grains going to about 1000 fps doesn’t give you a good margin when you need to be sure to kill.
If you need silence and if the guy is not killed at once and has time to roar, it is not good !
The US seals at the beginning were using 175 grains bullet in 9 para.
The weapon was a S&W Auto pistol Mle 59 (or something like that)
But the design of the S&W was not strong enough to support such loadings and they stopped because of too many accidents.
After they used 147 grains bullets.
- there is something people don’t understand.
When you have a silent gun and if it is well designed, you have the same velocity (about 1000 fps) and this for any caliber.
The only parameters you can play with are :
bullet weight (heavier it is better it is for momenteum)
bullet diameter and bullet shape (this is for terminal ballistics)
Therefore , for example, a 30 Nato or a 300 Weatherby magnum will be exactly the same if you can put the same bullet.