Introduced in 2023, the 400 Legend is yet another cartridge designed for legal use for big-game hunting in those States that have restricted legal chamberings to those using a cylindrical case and limited overall length. It launches bullets of 0.400-inch diameter and SAAMI pressure is 45,000 psi. With an overall cartridge length of 2.26-inches, this round will work in an AR-15 with the right bolt face. With a 16-inch barrel, it can generate muzzle energy approaching what the 308 Winchester produces. As such, it is certainly adequate for hunting any species in the U. S. where the need for shots past perhaps 150-yards is not an concern. It would be my choice for elk hunting in those States. As with any round headspacing on the case mouth, best practice is to apply a taper-crimp after seating the bullet. This helps to lock the bullet in place against chambering forces that might otherwise drive it into the case. I cannot too-strongly recommend getting a second seating-and-crimping die so you can have one adjusted to seat the bullet and the second adjusted to only taper-crimp the case mouth. Generally, attempting to do both operations in one step is a recipe for damaged and destroyed cases.