Normally these questions go "I have a ______, which is pretty good for _____, but I really want to buy a ______. Please, validate my decision, which I've already made."
My stock answer is "If you want a gun that'll do the job, use what you've got. If you want to buy a gun, buy a gun. You don't need my permission."
In this case, though, I'll change it up a bit. If you want a capable home defense carbine, use your M1, provided you've checked out your mags and ammo. If you just want to buy a gun, use your M1, provided you've checked out your mags and ammo, until you've saved up enough to get something better than a High Point.