I have yet to find one of his recommendations to be wrong.
You sir, have never spoken to my bride…. she can point out when I’ve been wrong with a PowerPoint presentation.
Using gauge pins to track erosion is something I have done for years, as it seemed to always track with performance. I am not yet believing that orifice size is the OP’s issue, as there are just too many success stories with the ‘smaller’ diameters. That RWS 1081 cap should ignite damp charcoal. Moisture? Something in the ignition channel? Are you swabbing and maybe pushing crud where you don’t want it? If swabbing, consider running a dry patch on a jag to the breech AFTER swabbing, then fire off a cap or two (too pricy at todays cap prices according to some, so maybe a good use for CCI caps), then pull that patch out. You should see a distinct scorch pattern on the patch. And what gun are you shooting? Assuming something with a chambered breech.
One last thing to consider, during our ‘collaboration’,
@chorizo suggested a steam cleaner for the breech, particularly chambered breeches. Purchased the one he recommended, and to be honest, it does quite number, removing ‘stuff’ from the breech of a clean gun. Surprising to see what comes out post a vigorous cleaning by pumping with soapy water.
Back to measuring orifice size for consistency. Gauge pins are the ‘best’, however, numbered drills and even weld tip cleaners can tell you what you need to know.
ca