Question #1 had that happen on my T/C Renegade. I discovered a spent cap had falled between the wood stock and the hammer. The result was to slow the fall of the hammer enough that the half cock caught. What probably happen is once you recocked the hammer the spent cap slipped out away from the hammer and the rifle fired fine..

Question #2 I am guessing that by using the Triple Se7en you increased the speed of the projectile enough that it made a different cutting appearance in the paper compared to a different propellant. If you want to test that theory better, shoot a projectile through a 1" pine board and look at the holes using the different powders you mentioned. This will tell you if any of the projectiles are starting to loose their true flight...

Question #3 Yep it usually means a patch with alcohol. I personally used denatured alcohol to do all my swabbing with. It works great, is inexpensive, easy to get at the local lumber yard, and it drys almost at once in the barrel what you leave behind off the patch. That way there is less danger of contamination of the next powder charge. It will also burn off when you fire the next charge...