Fat Elvis,
I just got around to chronoing my loads for my HK USC/UMP conversion. 16.5" barrel, 45 acp carbine.
my Load 6 is:
bullet: Hornady 200g XTP (hollow point)
brass: winchester (new)
primer: Fed 155
powder: 6.2g VV N320
OAL: 2.225"
my Load 7 is:
bullet: Hornady 230g Round Nose
brass: winchester (once-fired)
primer: WLP
powder: 5.5g VV N320
OAL: 2.270"
I normally shoot load 6 from my 4.1" 1911, where it averages 860fps with a std dev of 11.76 fps
that load shoots mean velocity of 1073.75 fps with a 10.64 fps std dev from the 16.5" barrel on the carbine. So, the extra 12.4" of barrel raises the velocity by 213 fps.
because i've been strongly advised not to shoot HP ammo through a suppressor, i'm working up a RN load, which is Load 7 above. From the carbine, mean velocity is 977.75 fps with a std dev of 3.49 fps!
I was shooting at a pace of about 1-shot every 2-3 seconds today, offhand, in the rain, with a bushnell holosight at 25yrd and nearly every one of my 5-shot groups was 4 shots inside 1.5" with 1 shot low and 3" left of the other 4.
(the first shot in my strings is almost always 30-60fps low, so i drop the first shot when calculating mean velocity and std dev.)
hope that helps some,