I agree here, with a straight .348 case necked to .50 being perhaps the largest case(.50 Alaskan) capable of chambering to a m71 Winchester and with top-end loads developing 1,760fps with a 600gr., I am not sure what case would be needed for a .50 cal 600gr. to make 2,000fps. I suggest that the 3" or 3-1/4" Nitro .50 case wouldn't fit so perhaps a new magnum Browning lever gun might be altered, but I don't know this for fact.
: Pressure wouldn't be high actually, as it is reasonable in the Nitro rifles, as long as a large enough case could be made to fit and work.