If your talking shooting a 50 grain pellet and sabot combination out of an inline it would work fine. What kind of accuracy you will have might vary, but some sabots I shoot at 85 grains and there really is not all that much recoil.

Pellets from a sidelock on the other hand might cause you some troubles. Ignition of the pellet might be a problem. Musket caps might set them off, but the big thing with sidelocks is the direction of the flame out of the fire channel in relation to the pellet. The pellet is meant to ignite from the bottom of the pellet where the sidelocks often times throw their flame to the side of the charge.