Pryodex will definately be more reliable on ignition in a sidelock. It is a reliable and accurate powder in my T/C renegade.

I used to have problems with 777, but got some pointers on websites and now I use fffg 777 in my T/C renegade with no problem. Here is what I do:

As stated, use the fffg powder (finer grain) which makes it easier for the grains to get into the side channel. Pour the first 15-20 gr of powder down the barrel, then tilt it toward the sidlock side and bump the rifle with your hand trying to get some grains down in the sidechannel. Then pour the rest of the load down and load the bullet. That along with the musket caps should do the trick. In fact, I use the CCI, magnum #11 caps with no problem.

P.S. That seems to work fine for the range, but to be extra sure for hunting I always do one more thing: I unscrew the nipple and pour a couple of grains in there, then replace the nipple. I do this whether using pyrodex or 777. Can't testify to whether this is totally safe, but I have not had any problem and never had a misfire in the field.