Missed that about the nipple, Roger- good catch - don't open up the flash hole in a new nipple, please. The channel and flash hole is designed to concentrate the flash, making the flash hotter and spraying out into the powder beneath the nipple - making the hole larger will not only allow more pressure to escape up, possibly as Roger says, throwing the hammer to 1/2 cock or worse, but will also reduce the intensity of the cap's flash, the reverse of what is desired. Too much pressure coming out the nipple throws cap fragments (possibly hammer parts as well) all over - and right back toward your shiny eyeball. Only a few years ago, a small cap fragment finally worked it's way out of my Wife's eye lid. For 30 years, she had a small 'green' spot in one eyelid. Oh yeah - an always wear protective eye wear.
If ignition is not good, try dumping the powder in, then thumping the side of the breech with your palm before loading the patched ball. Lifting the hammer to 1/2 bent position, will allow the air to escape the nipple which will also blow powder down to the area underneath the nipple, in the flash channel itself, which should guarantee good ignition.
