Load one chamber with a shell (.38 or downloaded 357 if you have one). Spin it. Without looking load another with a .357. Took me a wile to get the motion down so I could do this without looking.
Spin it, close the gate, dry fire till both are gone.
Focus on keeping that front sight rock steady. (I use the blackhawk because the GP100 still allows you to see the edges of the cartridges in the loaded chambers.)
I do something similar with DA revolvers. Have a partner load 2-3 rounds into your gun, while you load his. Then draw and fire rapidly into targets at 10 yards. The empty chambers simulate misfires, and you also can see every movement of the sights if you are flinching. I find I get the most education per round fired this way, which is important when ammo costs so much.