"During ML season, just about any ignition system is allowed, EXCEPT, one can't use the little 25 ACP cartridge and BP. Only 209, percussion cap, or flints allowed. "

Where are you reading this? I know guys who use the 25 ACP conversion primers, and know of no problems using them??

"Does not CO require an open ignition system and a pivioting hammer?"

No, this is not correct, Omegas have a closed / weatherproofignitionand they are legal.