Well my mind had one of those flashes of brilliance. One flash and it was gone.
The cartridge was a 577 not a 544.
If you google Martini you will get more info than you might want to see. There are sites there that give marking descriptions.
www.martinirifles.com sells parts and also has complete rifles, or will build you a custom.
Good luck on finding something out.
Best wishes, Bill