Then why do SEALS and Rangers make close quarters room entry....with M16/M4 rifles (same bullet as an AR15) rather than a pistol?
Im just sayin...the military does it best. And they enter close quarters rooms with an M4/M16 that shoots a 5.56 NATO bullet...the exact same bullet the AR15 shoots.
Because the military uses and trains with long range weapons...a rifle can be used for long range and short range, but a pistol, while more lethal is short range only.
A .223 caliber (5.56 in standard) bullet is the same diameter as a .22lr...it's longer, and roughly twice as heavy, and pointed (spitzer) not hollow point...and it's got a HUGE powder charge pushing it...Maybe five times that of a .22lr...meaning it's moving fast.
That is really good for you if you are close to it...that means it is going in and out without expanding and the wound is going to be very narrow in diameter.
Why? Because it's designed to engage targets at 300 meters.
It is all a function of muzzle velocity, sectional density and expansion after impact.
A .40 caliber, or 9mm is designed for close range.
They have a much higher sectional density and the charge is calculated for maximum expansion of the Hollow Point at a penetration of 7 to 10 inches.
This opens an enormous wound cavity, and creates hydrostatic shock (ballistic shockwaves).
Just youtube some ballistic gel tests and you'll see exactly what I am referring to.