I have found that WSR primers and TAC are the best combo. I switched primers from Rem 7.5's to WSR one time tuning a load and noted a 45fps speed increase in addition to a reduction in extreme spread from 60fps to 17-21fps.
It was kind of like getting laid and losing a bunch of weight.
I found the Winchester primers to be better with a couple of types of powders too. Just not night and day better like TAC.
Disclaimer: I have not tried every primer, powder and case fill volume combo. Far far far from what the industry has to offer as a matter of fact.
I have also found that powder burn rate vs bullet weight vs gas system length can have a serious effect on what people call clean burning powder or not. 1 could use a carbine length gas system shooting light bullets and report to the world that TAC is dirty and gets the bolt carrier and receiver all gummed up in 40 rounds. The other fella could have a MK12 with a rifle length system and shoot 77's and say it burns clean as ever.
As far as barrels fouling and dirty powders.... I believe the smoothness/quality of the barrel due to lack of places for fouling to hide is the cause of that more than powder type.
This stuff all matters. If your barrel is fouled when you go to try a new powder your test will be skewed.
When you clean the barrel down to bare metal it can take between 5 - 20 rounds to get "seasoned" again. If you do your test in this window your tests will be skewed again. Good smooth newer barrels take just a few rounds.
Crap barrels can take 20 rounds to season and then another 15 and they are fouled.
Good barrels with high round counts need more also to fill in the rough spots with copper
Blah Blah Blah.
