Bump!
I wanted to thank Layton and everyone else who has contributed on this subject. It's been a great help to me.
I finally settled on a load for my T3 Sporter. I got a chance to do some testing with the Lapua 139 Scenar. At first, I was running regular H4831 and I worked up to 49.0 grains for a very accurate load that was averaging 2851 fps out of my 24" barrel. Then, I went to buy powder and they were out of H4831, but had H4831SC. No problem, though. I did find that, due to the slightly shorter cut, I had to add half a grain to the load to get the identical performance, as this case likes to be full. So, using 49.5gr. H4831sc under the 139 Scenar, I'm getting 2850 and accuracy is .25-.35 MOA out to 500 and I'm still holding .5-.6 MOA at 850 yards. I just came back in from shooting some more of this load at 440 yards. Even in a 32mph wind that was shifting from my 6-7 o'clock, I had no trouble hitting 4" clay pigeons with every shot, then shooting the pieces after that. It was a much longer load development than what I'm used to, but I'm pretty happy at this point.
John