I recently acquired a Hepburn in 38-40 Remington. Trying to make cases so I took both 30-40 krag and 303 British, trimmed to the proper length and sized with a 38-50 Remington die. No luck. Chambers but the head just barely sticks out. Block won’t go up. I measured them against an original UMC 38-40 Remington cartridge and everything seems to match up. Someone suggested that the 38-50 is different enough from the 38-40 so I need a 38-40 Remington sizing die. CH4D can make one if I can wait 24 months. 
Any help would be appreciated.

I sized both the krag and 303 with a 38-50 Remington die. That didn’t solve the problem.
Thanks

For odd re-forming like this, I have had good luck boring sizing dies out of hard aluminum.   The aluminum is softer than the brass, so you don't even have to polish them.

CHRIS

I solved my problem. First I ordered cases from Buffalo arms. And then 25 from a super nice gentleman thru Gunbroker. Buffalo arms fit perfectly but the others didn’t. And they were in the original buffalo arms bag. Go figure.
So I took those, put the case in a c4hd 38-50 Remington die, hit it down with a hammer and punched the case out with a brass rod. Bingo. Worked like a charm. 
Went to the range today and started at 50, then 100 and finally 220 yards to see what would happen. 220 yards because an offhand match I go to is 220 not 200. Go figure. Took less than 15 rounds.
16 grains 4198 and a 250 gr bullet from an old ideal mould market 
38-255. Beautiful condition mould. 3” group at 220.

I wonder if using a small arbor press might be a bit more precise instead of whacking the cases with a hammer?