Personally, I think the 45-70 is the better choice. When it comes to subsonic loads, any caliber/cartridge you use is limited to velocity. The energy is increased by bullet weight. Firing a 405 grain bullet out of a 45 LC would be an interesting experiment. I shoot suppressed subsonics in 22 LR, 30-30, 308 and 45-70. In every instance, save the 22 LR, the bullets are heavy for caliber. 405 grain subsonics in my Marlin Guide Gun with a 16 inch barrel are "cat sneeze" quiet but hit hard. Up to 75 yds. the trajectory is suitable for good accuracy. Beyond that, the bullet starts to drop noticeably. The biggest challenge is finding a powder that provides a quiet suppressed report. I find Hogdgon Trail Boss and no filler to be the ticket. Other powders I have tried, while rendering subsonic velocities, were nonetheless loud when fired.
Since I don't load rimfires, I have found the Eley Subsonics to be the best. Velocities are right on the cusp of supersonic but remain subsonic through the suppressor and zero is virtually the same as the supersonic loads.
T.S.
