Yes, it seems that a copper jacket helps some.
I got to the range again and tried the 250gr QT over 135 gr FFFg 777 and no luck (5"). Then I tried the 200gr Shockwave and no luck (4.5"). The gun came alive with the 250 gr SST though, shooting 1.5". This was the best group I managed on the cold, windy day, slightly better even than the normal 100grain load/195gr Duplex DC that usually yields sub-1" groups. I still want to get ahold of some 260 gr DC bullets to try, though they won't likely work with my twist.
So here's another question. I can shoot either of the following two loads:
195gr Duplex DC, 1988 fps
Pluses- low recoil, flatter trajectory
Minues- price, long-range energy less (but soft lead, no copper)
250gr SST (250gr QT yields ~2100 fps so it's around there somewhere)
Pluses - much lower price, more long-range energy
Minuses - substantial recoil, worse trajectory
I am comfortable shooting at deer up to 300 yards (I use a rest or bipod, laser rangefinder past 150). I'm just curious what others would choose to shoot and why you'd prefer that choice. I'm also interested in target shooting out to 500 yds for the heck of it, and there appears to be 20+ inches difference in trajectory out there.