Alliant 3100 is a mythological powder, invented by a gun writer with the magic of typographical error. It's actually Alliant 300-MP--which I usually call in my notes 300.
Must also note that my particular Ruger No. 1B would average five shots under 1/2" at 100 yards, using Li'l Gun and 40-grain Ballistics Tips--if the brass was sorted for consistent neck thickness, and sized in my Lee Loader. If neck-sized in my Redding "S" die with unsorted cases, the same load would do around 3/4" at 100--for 10 shot-groups. But only with CCI 450 Magnum primers. Other SR primers did OK, but 450's were the deal, both with Li'l Gun and Alliant 300.
In that particular rifle 1680 never matched those powders, either in accuracy or velocity. But as has often been noted, rifles are individuals, and in my experience smaller cartridges result in even more individualism. One thing I noticed when playing a lot with the .221 Remington Fireball some years ago is that most rifles preferred either Li'l Gun or Reloder 7 with bullets around 40 grains, but not usually both.
