I have both the .25acp and Hubbard 209 breech plugs for the huntsman. I had the small rifle primers lying about, and I was willing the try the .25acp. After 3 rounds (yeah not that much) I have had no issues with ignition. I started the other day with 80gr of Pyrodex P, with the 360gr minnie's, and the rifle shoots dead on accurate at 50yrds.
Is there any reason to change back to a 209 primer in the Hubbard's plug, or if the .25acp is working... just stick to it?
What is the sheet test?