Fairly certain it is the Thompson Contender .600 Nitro Express for production firearms.
If you take every 600 N.E. double rifle out there and average out the weight then you are probably going to get about 15 lbs. I own one (Heym Jumbo 88B) and it's snug for me, but that's just me. 600 Nitro Express is a respected cartridge all over the world. It means business when you shoot. I really don't see the point at all in the 700 Nitro Express because the 600 is my favorite and does devastating performance on game
Probably, almost certainly, the .600 Nitro Express is the overall most power handgun bullet. Let me alter this answer by saying the .600 Nitro Express is a rifle round that one company made a pistol for. The most powerful handgun cartridge is the 500 S&W Magnum.
600 Nitro Express
Yes, here's several. .585 Nyati, .600 Nitro Express, .700 Nitro Express, 14.5x115... then you have weapons classed as cannons (20mm and up). The .50 BMG/12.7x99 isn't even remotely close to being the largest cartridge out there.
600 Nitro Express
There are several, such as the .600 Nitro Express and .700 Nitro Express, not to mention anything considered a cannon.
There are a very few revolvers made in caliber .600 Nitro Express. This was an African Big Game cartridge (elephants) and sells for about $140 per shot.
Like a Thompson Contender.
the hymy magnum express ,which fire the formidable ultra duty 600. nitro magnum express.
.700 Nitro Express. Although .50 is technically the largest caliber you can legally own without an NFA destructive device permit (which California will never allow), there are exceptions for some cartridges determined to be for sporting purposes (such as the .600 Nitro Express, .577 Tyrannousaur, .700 Nitro Express, etc.). California also has a ban specifically on rifles which fire the .50 Browning Machine Gun (BMG) cartridge.
No, the .600 Nitro Express is more powerful. Also, there is a .700 Nitro Express round that is designed for a rifle, but there is one handgun that will fire it.