Having never heard or seen of such a mod, I assumed it is a modern invention. Guess this is one more item on my list of why I'm not a SASS member. But, that doesn't stop me from supporting my local SASS clubs...or lending a helping hand when I can. I don't recall SASS polling clubs/members on this one...Ha!, but I do recall being polled about the Henry Big-boy & we all know how that went.
Yup, I've know that having high reliability C&B revolvers (and the skill to properly/promptly clear the rare malfunction) are essential to good placement in Frontiersman....That has been a significant factor in my placement over the years.
Other non-period innovations are already closing the gap on skillful use of true period-style weapons. Stage design can be a killer, too....when there are 6+ shotgun targets on stages & your the only shooter using a side-hammered-double.
Slim