Black River
Let us not be too hasty here. Yes the Richards/Mason is slightly different than the Open Top. Both are built on the 1851 Basic Frame. Barrel attachment is only slightly different. Very Slightly. The Uberti R/M Barrel assembly will swap right over to an Open Top.
How rapidly any two Open Top pattern guns foul out with BP is strictly a result of the individual set up. As with Original Colt sample examples, Uberti as well, no two are exactly alike. AS IN: I shoot a pair of Uberti 1851 R/M 38Spl that, with minor attention, will run an entire match. I have a pair of Open Tops that include 38Spl, 44 Colt and 45 Schofield, all run on the same frames. With minimal attention, they will run an entire match. I have a pair of 1851 Percussion guns, when running R&D conversion cylinders, will not run a full stage (yet) they also will not run a full stage without fouling the percussion cylinder (yet). And last but not least, a Pair of Capt. Schaeffer replicas, with R&D cylinders and percussion cylinders, that run a full match with either with no problems.
And, let us not forget, often, those folks who are new to the game, become confused with the nomenclature attached to certain offerings. So let us not beat him up too bad. Not his fault.
People can be Hazardous to Yer Health