Traditional .410 pattern distance was 25 yds per O'Connor, anyway. Somewhere in his writings he said that's what the folks at WW-Olin told him. That was before shotcups.
Your 0.013" bbl is about like my repro's 0.014" ("IM") Briley tube. Kinda strong for a skeet field. I use it for SC. A centered 30 yd midi or battue kinda dissolves with #9s or #8.5s. Most any 2.5" best quality domestic shell in #9 or #8.5 can make a case for 30 yd patterning, in accord with what you've read. IME, Win 3" #7.5s would merit 25 yd testing. I'd wager the 3" RP equivalent will be a 30 yd shell through your 0.013.
Dunno what to make of the the 0.030". My Win .410 "full" bbls run from 0.016" to 0.020". But I can't call them legit 35+ yd barrels. One exception is the RP 3" #6. Through a "full" 42 I get a % in the high 60s at 40 yds. In fact all the pellets fall within about 20-22". There is no "outer ring". Not quite sure what to do with it, though. Don't figure on taking 40 yd pokes at ditch parrots with it. Probably great for road-wrenching grouse.
