If you port a 10.5” barrel on the last 1”, will muzzle velocity reduce?
Posted by Itsivanthebearable@reddit | Firearms | View on Reddit | 11 comments
Suppose an Uzi barrel, where you port the 1” muzzle end. Would velocity reduce by 50-100 fps?
Suspectgore074@reddit
When it comes to porting, it really depends. If it was 3/32", I doubt you will see much loss in velocity.
If it was, say, 1/4", you'd see quite a large amount of velocity loss. This would be due to the bullet momentarily acting as a sealed plug, forcing the gasses to exit the large port. The bullet will exit the barrel, but a lot more slowly due to the friction of the rifling being greater than the forces acted on it by the gasses.
What kind of porting are we planning here? And to what purpose are you doing it for?
Itsivanthebearable@reddit (OP)
My friend has an Uzi and he wants to be able to keep ammo subsonic through a suppressor, whatever the brand of 147gr 9mm
Because some 147gr goes over the sound barrier
Suspectgore074@reddit
Hmm. The only way to effectively do this is to shorten the barrel, counter bore it, or use heavier ammo. Porting the barrel will reduce the velocity, but will likely be ineffective in noise suppression if there isn't anything to contain the gasses (think integral suppressed barrel)
Aren't those barrels interchangeable with some minor work? If that's the case, that could be an option if you can source a shorter barrel in the thread type you want.
Itsivanthebearable@reddit (OP)
I figured the porting might reduce the velocity more than shortening because the ports release gas pressure slightly earlier and, even if 1/2” of rifling left, that is friction that reduces the velocity.
Is that incorrect?
As in, would a 9.5” 9mm barrel have less muzzle velocity, or a 10.5” 9mm barrel with ports on the last inch of the barrel?
Suspectgore074@reddit
You are correct. Ports = less velocity. Ports farther from the muzzle equate to more velocity drops from friction. The question becomes, what other variables are you introducing when you port it.
My first thought is noise. Ports make a gun louder. The size of the port significantly changes the sound created, up to a certain point (usually near bore diameter). If your friend wants to keep the gun quiet, this should be considered.
On the other hand, this would be a significantly interesting thing to study, as I have always thought that porting affects velocity far more than muzzle flip.
Id say, go ahead and do it. The worst that comes from this is new information and a barrel that needs to be shortened.
Put_It_All_On_Eclk@reddit
The median velocity gain going from 9" to 10" is 3 ft/s.
https://firearmwiki.com/wiki/9mm_Velocity_by_Barrel_Length
Suspectgore074@reddit
Those numbers are based off of the assumptions made by Ballistics by the Inch. They only tested 2.9" - 6", and then 16" and 18" barrels through a variety of different weapon systems.
In other words, their numbers are accurate only to the extent of the actual numbers recieved through the barrels they had to test with. The lengths 15" - 7" are theoretically accurate but not tested
The only reason I say theoretically, is because I built a super longslide 1911 with a 16" barrel chambered in 460 rowland, and my performance blew the theoretical numbers they had out the water by more than 80fps. (That's not of course mentioning they didnt have as wide of a testing range for this cartridge as they did for 9mm, but point still stands)
Spartan543210@reddit
Will it reduce? Yes. By enough to be relevant on a short barreled 9mm? Probably not.
Itsivanthebearable@reddit (OP)
But 50 fps, or at most 100, realistic?
raz-0@reddit
http://www.ballisticsbytheinch.com/9luger.html
Spartan543210@reddit
Definitely less than 100, in my opinionated semi-informed guestimate, maybe as high as 50 depending on the size and amount of the porting.