Well if you clean your AR it won't jam as much, a rule all gun owners should follow. If you have to clear a jam in a scurmish, whacking your face is the least of your problems, you're pretty much SOL anyway.
A P90 is a nice gun. Light recoil, good penetration, accurate. But it is ergonomically awkward, and you can't see into the breech, so a brass check is impossible, and clearing a jam is going to be VERY difficult, expecially in combat. Reloading also isn't tactically efficiant, you can't drop and grab like with an AR, which can allow good 2-3 second reloads. You have to pull out a P90 mag so it takes twice as long. The mags are big too, so spare ammo won't be extreme. High ammo capacity is good, but rate of fire is a tad too high. Super short barrel makes it bad for medium ot long range, while AR can handle all much better. I have to say I'm an AR man.
Shotguns are always good choices for close range, but people tend to forget shot pattern doesn't truly spread for 30 or so feet, so a shotgun pattern at close range is as devistating as a slug. I want to get a Mossberg Cruiser as a home defense gun for this reason, my 870 Wingmaster is too big to make turns inside.
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