Using .62" caliber for an average 20 gauge bore diameter, a strip that is .9738" wide will cover the entire circumference of the bore( .62 x PI[3.1416] divided by 2 .9738".) For sanity, I am cutting strips at 1". :shocked2: :rotf: There is a bit of overlap, but not as much folding at the bottom as you have with the 1.25" wide strip.
[ 12 gauge(.73 caliber)x 3.1416, divided by 2 = 1.14" Use that 1.25 strip for a 12 gauge. ]
I am not expecting to load more than 1 oz. of shot in my 20 gauge fowler,( altho that may change with testing of different shot sizes). Until I am satisfied with the patterns I get with the shot sizes, and volumes that I use, I am not going to guess at how long the strip of fabric will have to be. From what I have tried I don't expect the column of shot in my barrel to be more than 1 1/2" long, and will probably be closer to 1", so a 4 inch strip should leave me plenty of excess material to stick out of the muzzle for trimming after the shot is poured into the "cup".
Remember to have a Razor-sharp knife for cutting that patch material! :shocked2: :wink: