Pretty much what TOM said--but will note that 120's aren't usually any problem. Only one that I know if is anything but a flat-base, the 120 Sierra GameKing HPBT, and it isn't all that long.
The longest .25 bullets are generally 115-117's, and while they'll all stabilize in a 1-10 twist it might not be ideal under certain conditions. But I've never had any trouble with any 115-120 grain .25's in a 1-10 here in Montana, even in the .250 Savage--though must also note that extra velocity doesn't make nearly as much difference in bullet stability as most handloaders think.
I just ran the 120-grain Nosler Partition in a 1-10 twist at 40 degrees and 3000 feet elevation (pretty typical deer hunting conditions in eastern Montana) through the best twist program available. The stability rating is 1.48 at 2650 fps (typical .250 Savage) and 1.59 at 3300, which is what I load the 120 to in my .257 Weatherby.
