I learned a procedure that is simple and has been 100% reliable in my Lyman GPR. After a shooting session,I remove the nipple and clean it and the barrel in hot water from the tap in a bucket in the tub. Once the barrel is cleaned and dried, I squirt WD-40 down the barrel until it runs out the breach end. Then I use Barricade or whatever rust preventative oil of your choice on a patch and wipe the bore and outside down. If I plan on shooting it within the next week or two, I just leave the barrel off and lay it on my cleaning table with the ramrod and oiled patch in the bore. Ok now with the barrel in this condition (well oiled) and off the stock, I hold the barrel over the waste basket and squirt carburetor cleaner down the barrel and in the snail before I screw in the nipple. I also squirt it liberal on a dry patch and pump it up and down in the bore. It will dry very quickly with no oil residue in the bore. Now with the bore in this condition, there is no need to snap a cap and it has been 100% reliable on the very first shot every time.
Now to keep it reliable on every shot after that, make sure you have the hammer on half cock and with a lightly damp patch, wipe the bore after every shot and push that patch down the bore quickly. That will force air out of the nipple and keep it clear for the next shot. You should be able to hear the air being forced through the nipple letting you know it is clear. With this procedure you should have reliable ignition from the very first shot till you get tired of shooting.