9 caliber is 0.09 inch, smaller than any standard ammunition made. 0.09 inch = 2.286 mm. Perhaps you were thinking "What caliber is 9 mm?". 9 mm = 0.354 inch = 35.4 caliber.
9 mm
No! 9mm = .35 caliber - .354 caliber!
It depends to an extent on what you are trying to do.
Yes. .38 special is a revolver cartridge and .380 is an auto cartridge. Also, the .38 will almost always have a heavier bullet and more muzzle energy than a .380. The .38 bullet is 0.357 inches in diameter while the .380 is 0.355 inches in diameter. Technically, the .380 cartridge is considered part of the 9 mm class of bullets. [9 mm x 19 mm = 9 mm Luger or 9 mm Parabellum, 9 mm x 18 mm = 9 mm Tokarov, and 9 mm x 17 mm = .380 ACP]
You can from some, but they have to be designed to shoot both.
No. Only use what is stamped on the barrel.
Roughly .275 or .28 caliber. Take MM divided by 25.4 (mm/inch) and you get caliber in hundredths of an inch.
.68 caliber is ABOUT 17mm.
No. 9mm and .40 are not interchangeable.
Short answer, a 9mm is smaller in diameter and lighter.
Yes they is a differnent. When people say "38" they usually mean .38 special, which is a revolver cartridge. .380 ACP is a semi-automatic cartridge. The bullet in a .380 cartridge, even though it's called .380, is actually very slightly smaller in diameter, and lighter than the bullet in a .38 cartridge. The .38 bullet is 0.357 inches in diameter while the .380 is 0.350 inches in diameter. Technically, the .380 cartridge is considered part of the 9 mm class of bullets. [9 mm x 19 mm = 9 mm Luger or 9 mm Parabellum, 9 mm x 18 mm = 9 mm Tokarov, and 9 mm x 17 mm = .380 ACP]