WHy does the Military use the M-16 carbine rather than a shotgun for house clearing like in the Middle East these days?
Shot count?
Penetration?
because everyone has rifles anyway?
To me shotguns mke more sense.
ZVP
A combination of factors which you mentioned.
Shot count - 12 Ga ammo is heavy, it's hard to carry a lot, and magazines hold less ammunition compared to rifles, obviously. Usually, considerably slower fire rate. Whether it's a pump action or an AA12, it's not really going to match up with the 900-1200 RPM cyclic rates that the rifles can do. The exception would be a Saiga12 or equivalent, but recoil on those things are insane especially compared to auto's with a system to reduce recoil like the AA12 (which only has a rate of fire of 300RPM).
Penetration - Shotguns have poor barrier and armor penetration compared to rifle cartridges.
To me shotguns mke more sense.
Why? I never really thought shotguns made much sense for 'room clearing'. What's the advantage? Spread is only about the size of a golf ball, you're not really going to be acquiring your targets faster. Recoil tends to be greater, as well.
IMO shotguns are for small moving objects like birds, at relatively short ranges. But you also have to lead shotguns more on moving targets, due to the lower muzzle velocity compared to a rifle.
Which also brings us back to the main subject of the thread. The shot gunner in the military needs training with the shotgun, and a rifle if he's going to be using both at any point. If not properly trained, then skills will suffer with whichever weapon has the weaker training. This also means more time and money specially training these people.