Tom,
I am finding that my double guns in the left tighter choked barrel at 40 yards are missing to the right, both 20s and 12s.
http://parkerguns.org/forums/showthr...907#post240907
I believe in this thread I wrote of an L.C. Smith that would tear up a shooting match target at 30 yards, but only if one held it to the right hand top corner of the target. Probably ideal for 40 yards.
Thus my theory is the guns/barrels are regulated to a specific distance. As my doubles are shooting to the right at 40 yards, I believe they have crossed the regulated point of impact and are now on their way to the right even more at the distances beyond 40. With your 10s shooting high, my theory is if you move closer it will be on the center of the target. Or maybe the opposite; with a large size shot, say buckshot that will have more drop due to being heavier, it may hit center at a longer distance. The Parker letters are interesting to see specific requests for certain patterns with a specific shot size at certain distances. Those 10s may like number 2s better than what we shoot at turkeys today. At least I can explain away my misses. Just my 2 cents.