Lockikng bolts on many break open guns are tapered to give compensation for wear (All are not). Selecting the amount of taper is always a compromise. With a steep taper there is the posibility of pressure upon the bolt being greater than it's friction causing it to "Squirt Back" giving a "Self Opening" gun upon firing. With a shallow taper there is the very real posibility of the bolt "Sticking" & requiring excessive force on the top lever to disengage it. Winchester chose (I was not in on their decision thus have no idea as to their reasonings) the shallow angle route & used the screw in the bottom of notch to deal with sticking prevention. Parker Bros on the other hand chose to go the Steep angle route & dealt with the posibility of bolt "Squirting Back" by using a little paralell side rail with minimal clearence on either side of the wedge bolt. In the event the bolt did try to slide back from pressure applied by the lift of the bbls these side rails having no caming action, their friction would stop further motion of the bolt, preventing the gun from "Blowing open".
Some other makers tried to hit a compromise taper which was shallow enough to prevent the gun opening yet steep enough to prevent a serious sticking problem. Generally they were reasonably successfull.
This all has little to do with the actual method of closing the gun & doesn't require a rocket scientist to understand, just enough common sense to figure the "Dangle of the Angle".
While at opposite ends of the spectrum, both the Winchester & Parker methods proved to be successful, proving I suppose, there really is "More than one way to Skin a Cat".
