If you have to pinch your caps to make them stay on, you're using the wrong size cap.
I can't offer any sugestions about the powder /ignition problem because I haven't used pyrodex in over 20 years. While I sometimes load Pinnacle or T7 these days, my primary powder is Grafs/Scheutzen/Kik/Goex.
The best nipple/cap combination I've found so far is #10 Remingtons and Treso nipples. The new Slix-shot nipples have the potential of being better because they will work with almost any size/brand of cap.
Fingers (Show Me MO smoke) McGee - AKA Man of Many Colts - Alter ego of Diabolical Ken; SASS Regulator 28564-L-TG; Rangemaster and stage writer extraordinaire; Frontiersman, Pistoleer, NRA Endowment Life, NMLRA, SAF, CCRKBA, STORM 327, SV115; Charter member, Central Ozarks Western Shooters
Cynic: A blackguard whose faulty vision see things as they are, not as they should be. Ambrose Bierce