Can a 300 FPS Airsoft Pistol/Rifle pop a balloon 25 feet away?

doubtful. it'll likely just bounce off. depends on the balloon. a latex party balloon, probably not. a Mylar balloon, maybe, but even then probably not. I've tried it before with a gun that shoots 310 and another that shoots 350 on both balloon types, with no popping/penetration. need a bb gun for that sort of thing, the airsoft pellets don't have enough mass/force to pop them.

Probably not it also depends on the type of ammo your using if you use .12 gram bbs then your shots will be less accurate and fly all over the place. If you go with .20 grams (most people do for assault rifles) it drops the FPS down to about 240 but it will be more accurate. If you use ,25 grams (mostly used for c02 pistols) will be more accurate then .20 but will drop the FPS from 190-215.

Thant aint hunting son but yes it would

yep. if you can hit it. airsoft guns aren't known for accuracy.

Why don't you try it?

But I can't imagine any airsoft gun doing that from any distance.