As far as stock design goes, one of the most important variables, critical to consistent holds without excessive tiring, is Length of Pull. For reasons I cannot fathom, most shooters these days want at least a 14" lop. And for serious offhand shooting, that is just too long for me. I am 6'2" tall, weigh 239 pounds, and have a 35" inseam. I prefer 13 1/2" lop. I find a 14" lop makes me have to reach for the front trigger, with my style of shooting. And that is standing as straight and erect as I can with head up, bringing the rifle to my eye, rather than squinching down and trying to find the sights by searching for a cheek weld. My favourite offhand rifle is a .50 cal. Chambers' Virginia Rifle @ 10 pounds. It is forward heavy enough with that C weight barrel to be very steady to hold, and is particularly satisfying off a plank or table, shooting consistent small groups at 50 - 60 yards.
I have never been to Friendship so I have no idea how I'd fare against American marksmen and women. But we have an annual BC Rendezvous - ten days of shooing competition, and I have been very successful there, in both trail type competition and target shooting, almost all offhand.
And I have received immense enjoyment shooting with some very capable members of this site. I have much admiration for those who post such excellent targets in our postal matches. This is wonderful practice, and I encourage more of you to participate. With dedication you will see your skill improve.