I shot the 10.3 heavies in my BSA for few years in HFT with some success. In the BSA barrel they are great, but I found the pellets come in 2 distinct types. They differed in the inside of the skirt, some had 2 angles and resembled a bismag from behind, the others looked like regular 8.44's in the back. The type with the 2 angle pressing inside the skirt would not group the others would. They did take less wind with only a very slightly more pronounced trajectory.
I also found they did not like faster twist barrels, the BSA was 18.5" twist. In a 16" twist they where still pellet on pellet in still air but suffered the Magnus effect in a stiff wind, when the wind was from the left they barely moved but when it was from the right they dropped massively! I tried to learn this but gave up and switched to 8.4's in faster twist barrels.
So in a slow barrel they are great and really do buck the wind at a small trajectory price. The trajectory is constant, wind is not so I figured reducing the variable was worth it! What ever pellet you shoot you have a trajectory to learn.
I have not shot the heavies for a while, I have been trying to find a setup that shoots lighter pellets but also bucks the wind, like Brian I have measured a bc of 0.0263 from jsb 8.44's using a down range chrono and am currently shooting flatter than that gun did but have not measured the new bc yet.
HFT, for people with only 2 buttucks!
VooDoo TwoTwo The next chapter.