Not a powder problem, unless you loads are not getting a full burn to start with.
Hence we need to take the problem all the way back to barrel harmonic's, being that differ loads/ different powders will have the bullet existing the muzzle in different points of the muzzles oblong movement instead.
Hence the muzzle will be traveling in a oblong circle as the bullet is traveling down the barrel (not up and down, but the axes direction off to one side from top to bottom instead),
And your trying to get the bullet to exit the muzzle when its at is stillest points in movement, being either the crest of trough, with any give load.
So when one load will have the bullet existing the muzzle at either the crest or through, then rifle will shot it tightest groups. But change the load, which changes the barrel harmonics as well, and this load may have the bullet exiting between the crest and trough points instead, and will increase the group sizing instead.
Also to point out, as the barrel gets hotter, it increases the movement of the barrel harmonics, and this may be what you are seeing, being that as you heat the barrel up more with the next load, it's changing the barrel harmonics to now get the bullet with the new load to exist the muzzle at one of the crest or through now instead.
So same gun, same load, and just different weather temps has this same gun shooting differently, all due to barrel harmonies/muzzle movement.
Summer time and we can see the barrel harmonics on the grouping and where the bullets are leaving the muzzle in the oblong path of the muzzle,
Winter time with the powder not pushing the bullet as fast, and we again, see the harmonics of the barrel oval movement and where the bullets are leaving the muzzle instead.
Note, if you over lay the two target and draw in the muzzle oblong movement, we can see the the crest is about the 2:00 O'clock postion, and the trough is about the 8:00Oclock position for this barrel. So summer loads has the bullet leaving the muzzle around the trough of the muzzle movement, while the winter time has the bullet leaving the muzzle more between the trough to crest on the right hand side (with one shot that has higher SD, and ended up leaving the muzzle on the other side of the crest to trough instead.
http://www.ar15.com/forums/t_6_42/457743_30___40__temp_difference_causes_this_much_variation___Update__pics_should_work_now_.html
So again, 4064 to push a round to 3K, then 4895 to push the same bullet to 3K, since the burn rate of the powder is different, so will be the barrel harmonics of the muzzle between the too loads, and where the muzzle will be in it's moment in regards to crest and trough when the bullet exists the muzzle.
P.S, To figure out the direction of the oblong muzzle movement in motion, it will always be counter clock wise of the barrel rifling.