I've had a 544 for years. Shoot it a bit, but find that reloading the .44-40 is a PITA, as you can't use carbide dies like a straight-wall case. That, and the case-mouths are very thin and fragile...I bet Starline has thicker case-mouthed brass, but I've never acquired any to try. I believe I will pin gauge the 544 cylinder, then drop a pin gauge down the barrel and compare it with a model 29 (.44) to see the difference. Of course, this won't be groove diameter, but bore.