I load a cut down 2 7/8" 10 gauge hull for my 1873 damascus charles daly SxS with 1 5/8 oz BPI nickel plated shot along with a 100 grains of FG. Pattern never seems consistent whatever load i've tried in the old gun. I can tell you my copper plated chilled lead and un coated plain old magnum lead shot is way harder than the junky BPI nickel plated shot. I got suckered in to buying some to improve patterns was was harder alloy to increase pentration and TKO value. Nope, the BPI nickel plated shot is super soft vs my magnum bare lead shot and every copper plated shot i have laying around. Easy test. Saw a guy on youtube do it to give credit to. Just set one shot on another and slowly sweeze in a pliers. The BPI nickel plated shot flattens first every time.
I would have to guess the reason the shallow cut wad was over pressured is because it didnt open up and release the pellets. Don't really know myself since everthing was exactly the same in the load accept for the LENGTH of the wad slits. Its the only thing that tells me what happened imo. Thats why the shotgun load books tell you to follow the load data to a "T". There really isnt any powder charge ladder testing data out there that im aware of. I have experiemented with my damasus and black powder loads...but thats on me if something goes south.
I did try some 2oz loads with another powder. I found three loads with all the same components with three different powder charges. I found the load with 39 and 40 grains first. I tried 39 grains. It shattered my 10 guage browning gold buffer and broke off an aluminum side plate pin! Didnt know it happened and hunted with it one morning to find out i had plastic chunks in the chamber. I did not know it happened that day and never tried the load again because the recoil felt like 2ce the spank it normally did. I found the 36 grain load after the fact and stuck with it (and replaced my gun parts). It patterned really good but no where as good as a federal 2oz flight control load. The 2.5 oz loads will pattern WAY tighter than the 2oz factory flight control wads.IMO your not going to get much help with sbotgun shell reloading because everyone will tell you to folllow what ever load data to a "T". I will rotate my 10 gauge modern hulls and wads for data because internally they are all made the same. The 12 gauge hulls are different inside. Never loaded for a 12 yet. I drew my turkey myself...lol. I I picked up a roll of 3m usps packing paper at a Micheals crafts for $3.59 with coupon. Think it was 30"x 30'. Made for cheap 55 yard targets. If I remember right Those were eight or ten inch circles in the middle. I've been reloading centerfire and casting Over 30 years, but shotgun reloading was a new venture to me and just started a few years ago. Every time I asked a question I was told but I was gonna blow my damascus gun up...lol. I've shot at hundreds of times with up to a hundred and sixteen grains of Dupont FG and 1 5/8" loads. Are you even tried cutting down plastic wads and adding buffer. They were the tough wads. They never opened up and the patterns were horrible...lol. But zero pressure signs because to me a 100 grains of FG is similar to a 20 gauge load or light 12 gauge trap load for pressure. Shotgun scientists made homemade flight comtrol wads. Imo you'll never get the cuts consistently enough to get good consistent patterns. Your better off getting some sample wads in every co figuration and pattern them yourself. I would also pick a choke to use and stick with it for testing.
