Both Shinsung and Sam Yang make a 50 caliber air rifle. The largest caliber Weinrauch makes is a .25 caliber.
Depends on what type of gun you are talking about. A pistol it is either .357 magnum or 44/40 Winchester which uses a rifle caliber size round in a six shooter for interchangeable use. Rifles would be 50 cal. m107 but the most effective round is a 416. The most powerful pistols are the Desert Eagle .50 caliber and the .500 Smith&Wesson
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.223
50 caliber
No real way to answer, since there are a number of pistols that fire rifle caliber ammunition. There has even been a bolt action pistol mde in caliber .50 BMG, and a revolver in .600 Nitro Express (an elephant rifle cartridge). In the traditional revolver type, among the MORE powerful may be the .500 S&W, the .460, and some of the Linebaugh and Cassul cartridges. There is a point reached where a cartridge may be possible, but have no practical use. If a handgun has so much recoil that it cannot be fired, or weighs more than a rifle- what's the point?
.500 Smith & Wesson Magnum is the most powerful dedicated handgun cartridge. However, pistols such as Thompson-Center Contender are capable of chambering rifle cartridges such as .45-70 and .30-30.
You will need the services of a good gunsmith.
No
No
This can be tricky because not all vest are the same,vest that cops use can usually be pierced by medium caliber rifles like a 30-30 or AK-47 or high caliber hand guns like .44 mag, but the dragon armor as they call it they some times use in the army can withstand a 50 caliber rifle,the most powerful rifle every made beside armor piercing rounds,but funny enough a 22 mag can pierce a normal vest,even though its not very powerful if its a full copper jacket it can pierce,thats because its such a small bullet that it does not take as much power to pierce objects as a large 45 caliber or 50 caliber would.
Take the rifle to a gun shop so they can figure out what make, model and caliber rifle you have. There is no 84 caliber long rifle.