Hi Fingers, thanks for the reply. The Pietta Paterson nipples are the same length as the Pietta 1851, 1858, and 1860.
The main reason I ordered the SliX-Shot nipples was to minimize hammer blow back when I lighten the Paterson hammer spring.
I think I will make a jig for my mini-lathe to shorten the SliX-Shot nipples by 0.010".
IMO this is another example of a third party vendor not doing their homework.