JP,
One of the very best, if not the best powders for the Gibbs style cartridges is the old, no longer made, H-870 or AA-8700. This powder produces the very best accuracy and velocity in my 240 Laser (3,800 fps w 1,000 yard groups of 4 inches with the 105 Berger VLD). You can buy 8# containers of pull down 870 from the Brass Man, on line. But if you were wanting to go with a totally new powder, still in production, I would look at R-22 or VN-560. However, 4831 and 4350 while not giving peak velocity but will give excellent accuracy.

4895 is to fast burning to take advantage of the case capacity of the Gibbs. You really need a powder for a long powder colum and R-22 is very close to the burn rate of 870 or 8700.
Ed

Rapier

Thanks for the suggestions. I have 4831,so I think I will try this first.

jplonghunter

the best bullets I have used
 

I have been shooting 25-06 since 1971 (that is 40 years). the best bullet in terms of accuracy is the 115 gr Nosler Ballistic tips, by far. Second best is the 120 gr sierra HPBT. There are now match bullets for the 25 caliber but I haven't had a chance to check them out. I have stuck with bullets for hunting whitetails. for varmint bullets - try the 85 Gr NOlser BT as well.