Firstly,it's not M4. It's Colt M727 which is carbine version of the M16A2. Premature version of the M4 series which don't has rail attached upper receiver with aluminium CAR-15 type stock and several small differences. Both SAT and Maroon Berets changed their old M727 models with M4 and Hk416A5 rifles but SAS are still using them with the M4s in limited numbers.
PÖH is using SIG 516 Patrol rifles with the Sarsılmaz made M4A1s as standrat service rifle. They bought 5.000 SIG516 rifles to change their old M16 variants. Check the previous PÖH images ofthis thread, they are all using SIG516. M16s are used still in PÖH trainings but thats all...
Ans also try to do CQB with a 20" barreled rifle. I bet you will very enjoy.
Secondly. 5.56 carbine rifles are much more suitable to special forces, wich are more ligtht, compact and easy to control with more rate of fire.The troops like special forces, they got much more spesific equipment for the special missions and longer mission times unlike the other infantry types. So they can carry more equipment and ammo. Also the 7.62 rifles have less stopping power under the 200 metres range because of their kynetic energy remains high in close distance and they can't spread in the body, just ream unlike the 5.56 rifles.
Also with the M885A1 ammunition which is usinb by us army since 2010, 5.56 ammunution became only 16 joule less lethal than a standart 7.62 NATO ammunition. So with this facts, 7.62 is only advandegeous as used in squad support roles like DMRs, sniper rifles and general purpose machine guns. It's not just only for us. The rest of the modern world is also uses 5.56 ol similar ammunuion (like 5.45 or 5.8mm) because of all this stuff...
"Kontrolsüz güç güç değildir"
Also the weapon preferences of the SWAT teams changes state to state. I saw HK 53, SIG SG550 series, Micro Galil, HK416 and HK G36Cs als well as M4s and local AR-15 clones. But for the FBI SWAT and HRT teams, M4 and HK416s are popular to use...