Yes I have a bunch of airsoft gun's and i have used ammo that is the wrong size... and i clogged the gun and had to take it apart to get it out.
I use .20g blaster bb's. They are quite expensive, but if you use low quality ammo it will wreck the gun.
the m16 uses 5.56 caliber ammo
Yes- with ANY gun, only use ammunition intended for that gun.
.25
Well, spring airsoft guns use an internal spring to fire the ammo and by auto you could be referring to either Auto Electric Guns (AEG's) which are quite popular and my personal favorite. AEG's use a rechargeable battery to operate a motor which fires the ammo that way. Have fun.
Only use proper air soft or paintball cartridges with launchers like that.
.380 ACP
45+70 Government
It will be printed on the barrel
The HK 4.6×30mm cartridge.
CR2032 COIN STYLE
Take it to a gunsmith for verification.