The Omega does not offer a nipple for percussion caps. Due to the design of the falling block with a firing pin in the block it would be difficult to make it work with a percussion cap as the firing pin would not contact enough of the surface of a cap to detonate it. A machinist could make it work but the expense would be high. I could come up with a working system which would require rework of the firing pin to a much larger one and reworking the breechplug to take a standard nipple. Not very practical. Personally I would probably stay with one of the sidelocks but some of the bolt inlines are OK and have multiple nipple availability.