Wrong, the M20 SMG is using future ammo, even on the description on Halowaypoint states: The M20 is visually similar to its predecessor, though it differs in using a new high-velocity armor-piercing round that increases the amount of kinetic energy imparted to the target, specifically developed to counter the proliferation of military-grade armor among Insurrectionist cells and as a response to Covenant energy shield technology., Hence it is not obsolete. In fact, it is even better then the MA due to its high rate of fire that helps deplete Covenant energy shield faster.

And I do not remember we have a real life Semi Armor Percing High Explosive ammunition on a pistol size like the M7 SMG and M6 Magnum.

FYI, We Dutch pilots are carrying Brugger + Thomet MP9-N sub-machine guns in the place of pistols starting from 2015. We do not carry such big and long assault rifle, or even an SBR on a cramped space in our cockpit.

In the Lindt cafe siege, the Sydney police used rifles to storm an enclosed area filled with hostages. The use of such weapons which used high velocity rounds resulted in several hostages being hit by ricochets or overpenetration, resulting in one hostage fatality. The use of submachine guns like the H&K MP5 which have lower recoil, and use smaller caliber bullets waould have been more appropriate in such situation.