I have a Clark Midweight barrel on mine. They use Lothar Walthar blanks. It shoots most anything well but really likes Aguila Pistol Match.
I like the looks of that rifle. Looks like that barrel is about 22" long. I know some of the guys at my club use GM barrels and they don't seem to be very finicky. My Ruger factory hammer forged target barrel is the most finicky sob I've ever had. I'm glad I finally found some ammo it likes: