.327 FM SP101 - Why the tapered cylinder?

[sceva]

Seems odd that Ruger would do that for such a high pressure round.
Is the remaining thickness enough to safely withstand a steady diet of 100 grain AE ammo?

Looks a little odd but I very much doubt it effects the strength of the cylinder. The tapering is at the front where the walls are thicker due to the cylinder throats and I imagine the wall thickness is still close to the walls at the rear end.