30-40 Krag is a cartridge also called 30 Army. It uses a 30 caliber bullet and 40 grains of smokeless powder.
7.62X39mm
Unless you are in a life or death/survival situation, NEVER SHOOT AMMUNITION THAT IS NOT DESIGNED FOR YOUR WEAPON!!!!!!!!!!!
5.56mm
Choosing the best weapon for self defense is a matter of personal preference. The .45 ACP is generally considered a very good defense weapon. There are very few handguns that shoot a larger projectile, but bullet size is a trade off with capacity (how many rounds a pistol can hold). Typically, a .45 ACP pistol holds 7-8 rounds, compared to a 9mm's 14 rounds or more. If one is expecting to be in a prolonged gun fight, one might prefer having more rounds.
magazines available in 20, 30 & 40 rounds
The Glock 17 (full-size 9mm) holds 17 rounds in a factory magazine. The Glock 19 (compact 9mm) holds 15 rounds in a factory magazine. The Glock 26 (teeny-tiny 9mm) holds 10 rounds in a factory magazine. The Glock 17L/34 (competition) also holds 17 rounds.
The Glock 17 (full-size 9mm) holds 17 rounds in a factory magazine. The Glock 19 (compact 9mm) holds 15 rounds in a factory magazine. The Glock 26 (teeny-tiny 9mm) holds 10 rounds in a factory magazine. The Glock 17L/34 (competition) also holds 17 rounds.
Caliber is the size designation for rifle and handgun bullets. Guage is the size designation for shotgun rounds.
5.56x45
You need to see a gunsmith.
6 1/2 inch rounds
the size varies since there are balls that are designed for kids to make it easier to shoot with