My reasoning for a bevel base is that when a bullet which fits revolver cylinder throats which are larger in diameter than the barrel groove diameter, a bevel base is less likely to drag a "fin" off the base of the bullet, as it is extruded into the smaller diameter barrel.
A bevel base does not present a tiny, sharp corner, having a lower heat capacity, which is more likely to result in "cupping" or ablative deposit of leading to the bore in heavy loads.
A bevel base starts more easily into the case mouth and is less prone to buckle the case or damage the bullet heel in seating.
The usual complaint most people have of bevel based bullets, picking up a ring of bullet lubricant which may attack powder, and therefore requiring laborious wiping of the bullet base, I have found to be a non-issue if you use a concave base punch in your bullet sizing and lubricating die, which "fits" the bullet base and creates a positive seal around the bullet. It is also a non-issue if you use the Star bullet sizer, or if you use any of the tumble-on film lubes like Lee Liquid Alox or LSStuff 45-45-10 and a push-through sizer.
Some people claim that a bevel-based bullet is "disturbed" upon muzzle exit and that a flat, square base is more accurate. I have recovered many fired bullets of my designs from Accurate molds, shot with full charges and 1:30 tin-lead alloy from Roto Metals, and NO bevel remained on the fired bullet, it having been obliterated by base upset upon firing. However, MORE important is that there was no cupping or finning of the base in full revolver charges over 900 fps, which I have frequently observed in soft flat-based bullets.
Accuracy of my bevel-based designs, when cast of 1:30 alloy in molds which drop correct diameter which "fits" is excellent. A charge of 6 grains of Bullseye approximates factory load velocity in the .44-40 with 43-206H and is accurate in my vintage Colts, as shown below.
Not bad for a 71-year-old curmudgeon at 25 yards using fixed sight off sandbags.