First, check to see that you have a BB gun, and not a pellet gun. Both pellets and BBs are made in .177 cal. A pellet gun will not shoot BBs (in most cases) If your gun IS a BB gun, you will need a gunsmith to check it for damage, stuck items in the barrel, etc.
Most Sporting goods stores carry them. .177 will also fit your air gun.
Any air gun or rifle that uses a .177 Caliber pellet can use the Gamo .177 Red Fire Pellet. No matter who makes the air gun. The Caliber .177 is universal to all .177 caliber pellet guns or rifles.
Made by WHO.
Realistically, you don't even attempt to.
It depends on the air rifle. All 177 air pistols and rifles fire 177 ammo. Some will fire, only pellets. Some can only fire, BB's. But, some can shoot both. And. Brake barrel air weapons can fire, special darts. But, DON'T, fire darts through a rifled barrel. You can do it but it can damage it. Only through a smooth bore barrel. When in doubt, check with the maker of YOUR gun.
It would help if you stated the manufacture and model of the air gun you are asking about.
There is no ONE most powerful air gun. But there is a class of air guns that are the most powerful. This is a PCP (PreCharged Pneumatic) class of air guns. They require a scuba tank or special pump to charge them to 3000 PSI. A normal air gun holds about 800 to 1000 PSI. The PCP rifles come in all calibers from .177 to a whopping 50 Caliber That is capable of bringing down a deer or Boar.There is no ONE most powerful air gun. But there is a class of air guns that are the most powerful. This is a PCP (PreCharged Pneumatic) class of air guns. They require a scuba tank or special pump to charge them to 3000 PSI. A normal air gun holds about 800 to 1000 PSI. The PCP rifles come in all calibers from .177 to a whopping 50 Caliber That is capable of bringing down a deer or Boar.
Not normally. BB are 177 cal, air soft is 6mm
use a .177 cleaning rod to force it back into the breech.
I suggest: JSB diabolo, Crosman premier, predator polymag see: http://www.pyramydair.com/pellets
I assume you are asking about air guns, if so then it would be helpful if you stated the model. Most air guns can accept all weights of pellet grains as long as the pellet is the correct caliber. In other words you can not use a .22 pellet in a .177 caliber pellet gun but you can use different weight pellets as long as they are .177 for that gun.