6mm bb's
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.
airsoft uses 6mm bbs. Perhaps you are talking about weight? .20 gram is good.
Standard 16 gauge shotgun shells.
If there's varying sizes of airsoft pellets, then each size will only work for airsoft guns intended to take that size pellet. Others will be either too small or too large, and could end up damaging your airsoft gun, or even getting stuck in the barrel.
You need to submit the kind of firearm is it? Pistol, rifle, shotgun?
Try cleaning it, different ammo. If that doesn't work, take it to a gunsmith.
Take it back and get a new one. Trust me I had one and my new one works fine.
Those I've seen take 2 3/4 or shorter.
Without more information, my suggestion is you take it to a qualified gunsmith for a safety check.
It takes about 6 years for bio bb's to break down completely.
None. Some handguns have been made that will fire .45 Long Colt revolver rounds and .410 shotgun shells, but that does not mean that you can take any .410 shotgun and stick .45 handgun ammo in there.
.410 ammo