Put some numbers on "so-so" results so we can see what it will take to make you happy. My old 13 twist is happy with 257420 (at .257) in 1 to 20 with 6.8 grains of H108 and Federal small pistol match primers. I think the numbers will show that it is being over spun and I guess I should try a little heavier bullet sometime.

Schuetzendave's #'s indicate my bullets may be too slow.  I have noticed 1-2 foulers help before shooting for groups.  1600 fps. average seem to open my groups to 4x5 " @ 50 yds. and they close up to around 1 1/2 x2 " @ 1400 fps. average . I had a 4 shot 1/2 x 5/8 " group with the 25-85 @ 50 yds. but bullets were tipping @ 1325 fps. Too slow ?  @ 100 yds. same load, 10 rds., @ 2 1/4 x 2 1/4 " with bullets tipping .  This load is 7.6 grs. of imr 4227 , 25-85 bullet, 30:1, 257", SPG.   
W/the 257420 GC bullet, I've used 4.5 & 5.0 grs. of Unique @ 1556 & 1623 fps. average.  The groups of each @ 50 yds. were 5 1/4 x4 3/4 " & 7 x 3 3/4 " for 5 each.
I use Jamison brass, annealed & neck sized.   
Haven't tried breech seating yet.   
I slugged the bbl. but not @ muzzle and breech.  Just all the way through.  Seems to be .250-1 /257 ".   
I'll work w/the 25-85 ( favorite bullet ) more to see if I can eliminate the tipping.   
What kind of accuracy are you experiencing with your 25-20SS rifles ?  Maybe I'm expecting too much.
Thanks for the replies, this helps.

Dave,
I sized and lubed with spg some RCBS 25-85, Lyman #2 lead bullets today which I plan to load tomorrow ( sized .258" ) I plan to up the charges of imr 4227 one or two tenths at a time from the 7.6 gr. loads I had previously shot and mentioned in a previous post.  I will shoot through a Chrony and check for any high pressure signs.   
I checked the CPA site about the breech seater case and it's not recommended for a Winchester.  I may have to check out the breech seating later if I can't find a suitable fixed ammo combination.  Thanks for the replys.  Seems I have a way to go yet.