According to ANJRPC:
A3659Â – the fifty caliber ban – was added to the full Assembly agenda for Monday, June 24. This is the final version of this legislation, which has been changing from week to week over the past several months. It bans firearms that shoot centerfire cartridges of any caliber that attain a muzzle energy of 12,000 ft-lbs. or greater. Though limited grandfathering has been added in response to gun owner concerns, the firearms must be registered, cannot be passed down to heirs, and owners will be civilly liable for damages if the firearm is used in a crime. Additionally, the bill has been amended specifically to prevent anyone with a pending order for these firearms from taking possession of them.
I was worried, somewhere, legislators were going to figure out the idea of restricting firearms by muzzle energy rather than caliber. This would exempt all the large bore safari cartridges I can think of, in addition to preserving shotguns and muzzleloaders. The .408 Cheytac would still be legal, as would the .338 Lapua Magnum and .416 Barrett. Of course, this could be problematic if your hobby is creating wildcat rounds. As best I can tell, this law will have just about the same effect if they just banned the .50BMG by name. There are plenty of alternatives that have similar properties, but just not quite as much muzzle energy.
It’s amazing to me that politicians are just now getting so concerned about a cartridge that John Browning designed 100 years ago, and, to the best of my knowledge, has never been used to commit a crime anywhere in the United States.
UPDATE: Originally I missed the bit about the proposal requiring a centerfire cartridge. This means any muzzleloading firearm is not covered. I removed that bit.