Caps are designated by number (#10, #11, etc) by size, not the powder they are intended to ignite.
There are "Magnum" caps, meant for Pyrodex because it's harder to ignite, but I have used standard caps with no problem except I have found Pyrodex a much better cartridge propellant than Muzzle loader or Cap & Ball.
#11 caps are too large for your gun's nipples if they blow off. 30 gr of powder should not blow the caps off nipples unless the flash holes are too large, the caps are too large, or the hammer spring is too light. Try # 10 caps. CCI are a tiny bit smaller than Remington caps, try both for fit.
I would not use 30 gr of 777 in a Remington, but real BP or Pyrodex is OK, but probably max. Try 20 to 24 gr, and try something that burns better than Pyrodex in a front stuffer. Real Black Powder Goex or 777, Cleanshot, or other substitute.
You need more than just a snug fit, the seating of a ball should shave off a ring of lead as it seats. Try .454 balls.