Take it to a gunsmith.
The bore is the inside diameter of the barrel. Simply put, it's the hole down the middle of the barrel.
The bore is rifled so as to put a spin on the bullet. This spinning gives a greater accuracy to the bullet, especially over that of a smooth bore.
The G36 uses a proprietary magazine which isn't compatible with the STANAG-compatible C-drum magazines for rifles such as the AR-15. The G36 could use such a magazine, if such a magazine were manufactured for it. To the best of my knowledge, none are.
If you're referring to the Heckler & Koch G36, yes, it certainly can. It can put holes in people, too.
you can put a 3'' in a Remington 812 2 3/4" but eventually it'll blow the barrel, wouldn't recommend it.
How would load your powder and ball down the barrel ram it down to make sure it's tight in the barrel then you would put powder in the pan when the flint hits the metal it creates a spark lighting the powder in the pan then lighting the powder in the barrel making it fire.
holes
First, get the owner's manual for your pistol. Most are available at no charge from the maker of the pistol. Check that your pistol is unloaded. Then check it again. After checking that it IS unloaded, use a cleaning rod and patch holder to push a cleaning patch wet with gun cleaning solvent through the barrel. Let set for a few minutes. Then use the rod and a bore brush to scrub the bore. Then put the patch holder on the rod, and push a clean dry patch through the bore. Follow with a lightly oiled patch, and wipe down the exterior with a lightly oiled cloth.
no you cannot bore it to 340 but you can put a stroker crank in it and get to 390, 396 and even more
Helium.
Usually, liquor.
attach the hopper, fill it with paint, attach the co2 tank to the back end by screwing it in tight, screw in the barrel, put in the batteries, take it off safe, and you are set to shoot.