My longtime favourite offhand rifle is my .69 with straight octagonal 1 1/8" @ 31" length & simple trigger. The reason it shoots best for me standing, is it is a Caplock
having much faster ignition than ANY flintlock.
I can hold the .50 Beck with 44" swamped bl. slightly better than the short gun, but the slower ignition lets me down. It feels better, but the ignition lets me down, even
when I don't flinch from the "puff" in front of my face.
I wholly agree with Dan, though. The longer barrel is steadier to hold - unless the gun is too heavy for you.
My best standing score was a 99/100 on the standard 100yard target shot at 100yards. We were having an argument on rifle weight for best score offhand/standing.
The rifle was shot on a dare at the Barnet Rifle Club in Burnaby, B.C. in 1974 or 5. Seems to me the 10 ring was 1 1/4" in diameter. I dropped one out low, as the gun sagged. My timing was off
for that shot. I was stronger in those days than I am now.
It was a 22 pound Bench Rest rifle with 20X scope chambered for the Nato Round.
I guess the take from this, is that the heaviest gun you can shoot well, is the best. With open sights, the longer the sight radius, the greater the potential for the most accurate shooting.
With a shorter rifle, you can increase the felt weight of the barrel (better holding) by adopting the Olympic Style of Standing Shooting.