Re: Remington 260
For bullets of this weight in a 28" barrel, I use H4350; and H4831 also works. As the barrel length is decreased; I would favor the H4350 more. My load uses powder charges range of 43.5gr to 44.0gr of H4350. Pleasantly, I found that my 28" barrel load worked equally well in a 24" barrel, but that's probably just a fortunate coincidence.
I like Federal and CCI Match primers, and my experience suggests that can be swapped with very little consequence. I develop my loads with standard primers, then finish off by trying the same brand's match primers to see if they make a justifiable difference.
Often, a well developed load can work about as well with standard primers as it does with match primers. When funds and supplies permit, I use match primers, but a load that's developed as above tends to work quite well enough when I can't use my first choice.
I believe in doing my load develpment testing under as close a set of conditions as the load is intended to be primarily used. My match conditions tend to include milder weather, using a fully warmed up and fouled barrel in a sustained fire context. I try to duplicate these conditions for my load testing. Loads developed under significantly different conditions can go 'out of tune' in the midst of a match string of fire.
Match loads should be confirmed when employing significantly newer lots of components. It may pay to hold off producing complete new batches of ammo until this confirmation is successful.
Greg