Ken:
I've used 30-40 Krag barrels on old Toppers and SB2s. I've never had any problems when loading to factory duplicaton loads. I would not hesitate to use a 30-40 on any H&R Topper or NEF RIFLE action. My new 30-40 is on a early SB2 action, which is NOT approved for the current high pressure barrels. This last few days I've been putting Remington and Winchester factory 180 gr loads thru it, and my favorite handload. Shoot and enjoy.
Wally