The restriction for unexempted cartridges is that they be .50 or less between the rifling. Meaning if a .50 plug will slide down the bore it is too large.
Since there is a maximum pressure that can be reached you have a theoretical maximum of what you can do with near the max pressure in .50 caliber.
The maximum PSI most manufacturers seem to be willing to reach according to SAAMI specs is around 67,000 PSI.
You could make them hotter, but you want your typical cartridge to be at least several thousand PSI lower than a proof load, or it is just a matter of time before you blow yourself up when the chamber or barrel has some wear, or a slight barrel "obstruction" like a little moisture is present.
Further, when dealing with a cartridge with a huge amount of slow burning rifle powder you want some room for error. If all the powder does not burn exactly as anticipated you do not want to always be by design right near the exploding point. If it spikes a few thousand PSI due to some erratic powder burning you want to retain your arms and face.
That said, some proof loads go up around 100,000 PSI, so you could make a rifle much more powerful than anything that exists in 50 caliber if you build it robust enough.
The 12 Gauge rifle from hell gives a lot of theoretical room.
If a 12 gauge shotgun at .73 bore is legal to build capable of taking significantly more pressure, and firing significantly more powerful rounds, and is still not a DD because it is capable of firing standard 12 gauge shotshells, then there is no reason the same cannot be done with a 10 gauge, also a "sporting" caliber.
That means you have the potential to overbuild a 10 gauge. Assuming you build it capable of taking similar pressures you could make a serious monster of a gun in .775 caliber with 65,000 PSI specs. It just needs to be capable of firing standard 10 gauge shells as well as your extra long rounds.
As the .950JDJ demonstrates if you can get a sporting exemption for a custom round you can be well over .50 diameter.
Where you can really get powerful without becoming a destructive device is with muzzle loaders.
You can build a muzzle loader meant to take modern powders in modern pressures in any caliber you want within state laws.
That means cannons from those used to reenact battles from the civil war, to any modern muzzle loading design is perfectly fine.
Howitzer? No problem, well except for a place to shoot it. You are still responsible for each and every round you fire, and I don't know of many gun ranges that won't mind you blowing up significant portions of the range. You are limited by the curvature of the earth in being able to follow the 4th rule of the 4 rules, and need to keep shots within a range you can follow the 4th one from your current height on earth.
.4 Be sure of your target. Know what it is, what is in line with it and what is behind it. Never shoot at anything that you haven't positively identified.
Some people have thier own tanks with the actual guns. They simply sealed the breech and must use it as a muzzle loader to keep it from being a destructive device as it is certainly over .50 and not a sporting caliber.
What makes the .50 BMG great is not that it is the most powerful, but that it is a common cartridge used by forces around the world. That means someone who is not a millionaire can actualy afford to use it at the range.
The 12.7x99MM (.50BMG) is a NATO cartridge. So just like 9x19mm (9mm Parabellum) NATO, and 5.56x45mm NATO (.223 Remington close), 7.62x51 (.308 Winchester) etc it is widely available, even as surplus.
That means there will always be fuel to feed such a rifle all over the world, and while expensive is not $50+ a shot. You can find brass for such a gun on any modern battlefield. Where common machineguns like the M2 are used.
It is used to train forces around the world.
It is a common round.
Since there is a maximum pressure that can be reached you have a theoretical maximum of what you can do with near the max pressure in .50 caliber.
The maximum PSI most manufacturers seem to be willing to reach according to SAAMI specs is around 67,000 PSI.
You could make them hotter, but you want your typical cartridge to be at least several thousand PSI lower than a proof load, or it is just a matter of time before you blow yourself up when the chamber or barrel has some wear, or a slight barrel "obstruction" like a little moisture is present.
Further, when dealing with a cartridge with a huge amount of slow burning rifle powder you want some room for error. If all the powder does not burn exactly as anticipated you do not want to always be by design right near the exploding point. If it spikes a few thousand PSI due to some erratic powder burning you want to retain your arms and face.
That said, some proof loads go up around 100,000 PSI, so you could make a rifle much more powerful than anything that exists in 50 caliber if you build it robust enough.
The 12 Gauge rifle from hell gives a lot of theoretical room.
If a 12 gauge shotgun at .73 bore is legal to build capable of taking significantly more pressure, and firing significantly more powerful rounds, and is still not a DD because it is capable of firing standard 12 gauge shotshells, then there is no reason the same cannot be done with a 10 gauge, also a "sporting" caliber.
That means you have the potential to overbuild a 10 gauge. Assuming you build it capable of taking similar pressures you could make a serious monster of a gun in .775 caliber with 65,000 PSI specs. It just needs to be capable of firing standard 10 gauge shells as well as your extra long rounds.
As the .950JDJ demonstrates if you can get a sporting exemption for a custom round you can be well over .50 diameter.
Where you can really get powerful without becoming a destructive device is with muzzle loaders.
You can build a muzzle loader meant to take modern powders in modern pressures in any caliber you want within state laws.
That means cannons from those used to reenact battles from the civil war, to any modern muzzle loading design is perfectly fine.
Howitzer? No problem, well except for a place to shoot it. You are still responsible for each and every round you fire, and I don't know of many gun ranges that won't mind you blowing up significant portions of the range. You are limited by the curvature of the earth in being able to follow the 4th rule of the 4 rules, and need to keep shots within a range you can follow the 4th one from your current height on earth.
.4 Be sure of your target. Know what it is, what is in line with it and what is behind it. Never shoot at anything that you haven't positively identified.
Some people have thier own tanks with the actual guns. They simply sealed the breech and must use it as a muzzle loader to keep it from being a destructive device as it is certainly over .50 and not a sporting caliber.
What makes the .50 BMG great is not that it is the most powerful, but that it is a common cartridge used by forces around the world. That means someone who is not a millionaire can actualy afford to use it at the range.
The 12.7x99MM (.50BMG) is a NATO cartridge. So just like 9x19mm (9mm Parabellum) NATO, and 5.56x45mm NATO (.223 Remington close), 7.62x51 (.308 Winchester) etc it is widely available, even as surplus.
That means there will always be fuel to feed such a rifle all over the world, and while expensive is not $50+ a shot. You can find brass for such a gun on any modern battlefield. Where common machineguns like the M2 are used.
It is used to train forces around the world.
It is a common round.
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