gotsarock,
That's the Miller twist formula, generally considered the most reliable available--and what I've been playing with here to come up reasonable answers. It looks like any bullet under an inch long will stabilize to a certain extent, depending on conditions, and my guess is the 90-grain Sierra HPBT is under an inch, since the 100-grain MatchKing is about 1.09" long.
On a more material level, I've had the 100-grain Speer Hot-Cor stabilize fine even in cold weather at 2000 feet or so in eastern Montana, from the 1-14 twist of a .250 Savage (and the formula says it should, if marginally).
In my experience, one reason the 87 sometimes shoots well in 1-14 twists and the 100-grain doesn't the supposed 1-14 twists of older Savage 99's varied somewhat, because they were rifled on sine-bar machines. Some were apparently rifled on Mondays and Fridays, because I once owned an 99 .250 that turned out to have about a 1-15 twist. It would NOT shoot any 100-grain bullet, even the Speer, though it did fine with the 87. But all the other 1-14 twist .250's I've owned would shoot the 100 Speer and, often, the 100 Hornady Spire Point pretty well.
I've got enough of both of those 100-grain bullets to spare a little sampler pack if you want to try 'em.
