If you are asking about traditional BB guns, Not Airsoft. Then the answer is basically one size .177 Cal. At one time the BB's were .175 Cal but that was in the past and the difference is so minimal that it does not matter. Today's BB are made from Steel, Copper coated or Lead. One Size Fits All.
Not normally. BB are 177 cal, air soft is 6mm
Airsoft bbs are made up of plastic and are 6mm in diameter and are .24 cal, BBs however are metal and are .177 cal (4.5mm)
The 22 is slightly larger than the .177 cal. The 177 Pellet is almost the same diameter as the .175 BB.
4.5 mm and .177 Cal are the same size. It's just two different units of measurement. Millimeters verses Caliber.
.177 cal. Crosman, daisy, rws, beeman, marksman all make pellets in the .177 size
You will need 6mm plastic BB's. These can be gotten at most sporting goods stores these days. *There are also airsoft guns that shoot 8mm BB's. These are quite rare to see in the United States, so I'm betting that your gun is 6mm. .177 cal metal BB's or .22 cal metal BB's won't work in your airsoft gun.
A pistol that fires .177 diameter pellets.
Well, the .22 is bigger than a .177, but the "strength" depends on the action of the air rifle that shoots them. Certainly the .22 will have more hitting power assuming that the pellets are traveling at the same speed.
diameter
No. a 177 is a 4.5mm pellet. A 5mm is a 20 cal pellet. A 5.5mm is a 22 cal pellet Don't try it in the wrong airgun.
Gamo Hunter Extreme 1650 FPS - Air rifle .177 Cal Air Force TalonP 900 FPS air pistol .25 Cal Hatsan AT P1 Air Pistol .177 870 FPS The Air Force TalonP is faster in .25 Cal than the Hatsan .177 Cal