I got the following from Bowens website:

"The receivers are modified to accept oversize cylinders. The bolt notches of the 5-shot, unfluted cylinders fall between the chambers rather than over them where the chamber walls are thinnest. The longer cylinders accept cartridges loaded with longer, heavier bullets for superior hunting performance. Further, the cylinders feature free-wheeling ratchet and, where possible, recessed case heads to improve loading gate support."

So I guess its advisable on the heavy kickers where its possible. Rod if you are getting your cylinders from Bowen anyway, maybe mention the recessed case thing and he might be able to supply you, cant hurt to ask.