Gary, If you really have an 1891 cannon with sights graduated in Arshins, you are very fortunate, indeed. Almost all of these were converted to the metric system starting in 1917. If your rifle was made after 1916, it has sights with metric grads. One Arshin is equal to 28 inches or 711 mm, (711mm/25.4mm=27.9920"). Mike's version of this Russian cannon, (7.62mm x 54mm, rimmed) is the vaunted,
Sniper Model for which he forked out big bucks, proving himself, beyond a doubt, to really be a dufuss. It gets 6" to 8" at 100 with careful handloads or surplus ammo. And HE has a scope!! I said to him, "Ah, say, Mike do you think that you could get a grapeshot load into that rifle??"
Tracy