Re: Heaviest bullet for 22-250?
I ran some stability calculations using the Miller Stability formula on JBM Ballistics to see what I could find out. These calculations were run @ standard temperature and pressure, so they are not altitude corrected.
To my surprise, the Barnes 50g TSX does not stabilize in a 14 twist. The 45g TSX shows marginal stability, but does stabilize.
Another mono-metal option would be the Cutting Edge 40g Raptor. CE says it stabilizes in a 14 twist and the Miller formula agrees, though the stability factor again shows marginal stability.
The 60g Nosler partition does not stabilize.
Sierra says their 60g Varminter will stabilize, but couldn't verify that by calculation because I couldn't find a listing for bullet length. I wasn't able to do any calculations for the 63g Varminter for the same reason.
Couldn't find length info for the Winchester 64g Powerpoint, so no calculation for that one either.
Berger says their 55g Target bullet works in a 14 twist. Miller formula says no.
Obviously, there is some room for the "fudge factor" here. Any theoretical formula can only give you an idea of what to expect, but can't be definitive w/o testing. Where the formula and the bullet manufacturer disagree, I would be inclined to believe the manufacturer, but that is a judgement call.
Overall, it looks to me like you would be pretty safe in going with a 40-45g mono metal bullet. Likewise, up to 55g conventionally constructed bullets, such as the Hornady Spire Point, Sierra Gameking, Berger Target, etc. should work. Some 60g conventional bullets may work, as well, but you are starting to get into marginal territory there.
Alternatively, if you can borrow a 12 twist or faster .223, it will open your options considerably.