"A final comment on the 11 inch shorty M4/CAR-15 vs the MP5/10 or 40. I realize that you use what you can get. However, these comments about getting a rifle caliber vers a hand gun round are for the most part MOOT.
It is very difficult to get a 11 inch 5.56 to chrono over 2000 FPS with most of the ammo available. You might find the odd round that goes 2200 with a 55 grain bullet, but at that speed you are going to not much more performance than using a .22 hornet. It is very rare to get reliable expansion out of a 5.56 at sub 2500 fps velocities. Rifle bullets are meant to function at rifle velocities, If you make a jacket that reliably expands at 2000FPS, at 2600 Fps or 3200 FPS out of a 20 or 24 inch barrel that bullet is going to destruct like a balloon on a pin. at the same time, if you make a jacketed bullet that will hold together and expand at between 2800 and 3200 fps, when it hits 2400 fps, it will act like a FMJ and just drill a little hole."
Really? Where did you read this? Ever seen any type of gunshot wound to a person in real life? Besides, we bought our rifles off the shelf with 16" barrels.
The moot point is that pistol calibers don't even compare to rifle calibers in range and performance.
Ahhhh yeah, I've seen a lot of GSW's, far more than I hope anyone ever gets to see. Contact wounds to back of head, results of death squad activity, urban fighting and jungle fighting. I've seen 5.56, x51 and x39, 50 BMG, 300 winmag, 9, .38, 45, and some that might have been either .22 or .25. Yeah I have seen a lot of GSW's, some first hand as in they happened right in front of me, some left in the jungle to rot, some coming in on liters to get treated.
My statement was that a rifle caliber needed a rifle length barrel to use it's advantages in powder capacity and velocity. Putting a rifle round in a very short barrel when loaded with powders designed for long barrels gives away so much as to drop them below a pistol round fired from a carbine barrel. If you have 16 inch barrels you are really at the low end of the envelope for a 5.56 with current loadings.
The discussion on velocity parameters vs bullet construction can be found in any reloading manual. This is why you have blits and TNT bullets, game bullets with ratings for size of game and velocity of cartridge. A prairie dog type bullet meant to explosively expand on a 5 to 15 pound varmint, is going to make a massive but extremely shallow wound on a deer or human sized, like wise, a bullet constructed heavy enough for good penetration and expansion into Deer sized game, is going to act like a FMJ at velocities below its design parameter or on animals below its intended size. This is Basic Reloading 101. A FMJ below its velocity limits for tumbling is just a long range drill bit, small hole in, small hole out.
Do yourself a favor and buy a Chronograph. shoot your ammo over it and look and see where real world numbers put you. You can buy 10mm now that get 1440 fps from a 5 inch barrel. That fired from a 10 inch contender jumps up to 2000 FPS. That is factual data. A ten inch barrel contender in .223 has a very hard time reaching 2400FPS with any load in a 55 gr bullet, no chance at all with a 62 or 69 grain bullet. In fact the best I have seen with a 69 grain bullet is just over 1700 FPS out of a Ten inch barrel. adding an inch and half of barrel, will give about 130-180 FPS add-on.
My statement still stands, At the distances police operate, very, very rarely over 100 yards, (FBI stats put the average police "sniper" shot at under 70 yards.) in an urban environment, one can make the argument that a much larger bullet at very nearly the same velocity would work better. I am NOT saying that for a 250 yard shot the Mp5/10 would be better, but with in the parameters of under 100 yards, its works. And it works well.