6.5 Grendel. There are bolt actions and AR's out there. I have taken 15 deer from Arizona , Tennessee, and Alabama from 40 to 300 yds. Only one took more than 10 steps and all were dead by the time I walked up. Low recoil, accurate, and similar trajectories to 308.
It does happen. Had a newbie get hit with a simulation round in the arm, he rolled up into the fetal position and it took 5 minutes to uncurl him and get him back on his feet. We were hurting for recruits so they put him on a desk. It took 6 months and several other similar incidents during...
After seeing autopsies and reports from both 9mm and 40 S&W it all came down to cost. They are both efficient at what they do but 40 cost about 20-40 % depending on supply and the recoil differences already brought up made training a little more difficult.
H&K has lived on the legend of the MP-5 for a very long time. Don't know its current status but in the late 90s their customer service was a joke.
They sold the USP pistols to agencies with an aluminum framed prototype. Parts were impossible to get and early problems were many.
The UMP...
Beyond , because you want to , Why.
You lose a considerable amount of velocity/efficiency with a barrel that short,and as stated above the blast is a monster. ( I have only fired a 10 1/2 barreled 308 from a C.ontender).
If you have to have a 30 cal semi why not go witha 300 blk out. Much less...
Don't know if he is one but I spoke to several of the top shooter including Robbie Leatham 5 years ago. Leatham gets 100k plus rounds a year from several sponsors and he shoots a lot of it.
If you have ever seen Jerry shoot in person it's almost supernatural. You keep looking for a trick but...