Back to the carbine. Being Metford rifled (as Bruce says) may appear to be worn when its not (or not worn out).

Still this probably shoul.dn be shot wtih MK VII hardball. My MLM MK II (commercial export model), shoots heavy 200-210 grain round nose bullets at aroun 1950-2100 fps quite fine.

Giveit a try before 'rebarreling'.