Sierra is using a Colt with a 20" tube with their data.
They show 23.4 Gr. of WW748 as max., but vel. is low at 2,500FPS. They show Varget max at 23.9 Gr., I go up to 24.5
with no pressure signs. They show H4895 with 23.6Gr. max at
2,600FPS & they show TAC as the fastest with 24.0Gr. max at 2,750FPS.
In the Hodgdon 2006 Annual, the following did the best:
24" barrel
All the Max charges
Varget-23.7 Gr. at 2,737FPS
BL-C(2)-25.5 Gr. @ 2,738FPS
H335- 22.6 Gr. @2,738 FPS
H4895- 22.6GR. @ 2,727
Benchmark 22.8 Gr. @ 2,763FPS
H322- 21.8 Gr. @ 2,721FPS
I have had best results with Rem. 7 1/2Match & Fed. Match primers.
Sleddog, out of what I have read concerning the 223 with the 77Grain bullet I would try Varget, Benchmark, H4895 &
Tac, in that order, but all would be great choices.
I have seen more people using Varget with this bullet than any other, but for a source that kicks butt with H4895 as well as data for other rounds go to
www.geocities.com/graymist44
It goes without saying to work up slowly.
Hope this helps.