It is obvious to me that the problem is that the nipples are too small for the caps. If you were using #10 caps on #11 nipples, the cap would be difficult to get on the larger nipple. Your problem is the opposite and since there are no caps larger than #11 except musket caps, at least not in the U.S., that means that the nipples are too small. You aren't trying to use musket caps, are you? I don't know why both rifles would end up with undersized nipples unless you changed them yourself or if you bought both guns from the same person and he installed the wrong nipples. Another possiblilty is that the nipples have been filed or ground down for one reason or another. This could cause them to be undersized as well. Also, I would check the nose of the hammer for spent primers stuck in the nose of the hammer. This often happens and they have to be dug out with a sharp pointed instrument such as a dental pick. This is more likely to happen to the Lyman but could happen to either of them. A couple of new nipples are not that expensive, less than $10. Change them out, clean out the hammer noses and see if that doesn't solve your problem.
A little additional info: #10 nipples and caps are for revolvers. #11 nipples and caps are for rifles, shotguns and single shot handguns. Musket caps and their nipples were originally for military arms but have been adapted for use on rifles, pistols and shotguns as well as military arms by simply installing a special musket nipple in them. I don't think a musket cap offers any advantages over a #11 magnum cap. Neither is needed except when you are shooting a black powder substitute. Regular #11 caps are plenty hot for black powder. I've shot all kinds of rifles, underhammers, side hamers with a nipple drum, side hammers with a snail drum and side slappers and none gave me any trouble with regular #11 caps with black powder. :thumbsup:
This is just my opinion. It's free and worth every penny of it. :rotf: