I've already answered your questions via email but they are good for public information, so I'll do it again here.
The GP 100 is a fairly light gun, which will probably dictate a 160 gr to keep recoil pleasant for the type use you have for it. The XS will not feed in a lever gun, as the meplat is much wider than the FN, which is the bullet I'd recommend if you think you might want to use it in carbines. I've been able to hit a quart oil bottle quire regular at 100 yards, using the XS with hot 38 special loads from a 4 inch revolver, shooting off hand, with two hand hold. Speed being 1100 fps, which could have been faster with a slower powder. So it is plenty accurate, but the FN does have a better flight form, and is more accurate.
A bevel base is what I'd reccomend for Star users, flat base if for RCBS or Lyman sizers, and one doesn't want to use gas checks. However for wringing a carbine length barrel out, or a 357 revolver, a gas check bullet can churn out quite a bit more horsepower, with no leading and optimum accuracy. I strongly reccomend anyone wanting to shoot plainbase bullets to get our LBT bullet lube. It will take you to far higher levels of power and accuracy than any other lube, whether plain base, bevel base or gc.
The so called Keith bullet you have is quite typical of most mass production mold maker designs, which are set up to feed or chamber freely in any gun, accuracy be hanged, as long as it goes bang. Keith hated it and complained about it till he died. If I call a bullet a Keith, it is as exact a replica of his design as I know how to make, and they shoot like he claimed they did, if they fit the gun and if the gun is set up to the standard of the guns he shot. (Of coarse you know the manufactures sent him only custom shop guns once he became popular!?) The LBT lap kit will make most guns equal to what he unknowingly used.