The 91/30 specs included a round receiver, the "short" barrel and post-and-U-notch sights. One with an octagonal frame and 91/30-length barrel should properly be termed a 91 Dragoon Rifle or, if the s/n starts with KA3, a Cossack Rifle.
Ineresting point is regarding the receiver. MNs have their factory info on the BARREL, so it could be a factory rebuild of an older frame. Check the frame for date.
This one sounds interestng!
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What looks like an "r" is actually a GAMMA, standing in for "goda": "issue". You find the same thing on coins; I'm looking at a silver ruble right now marked "1897r". Very pretty. I'm sure your rifle is likewise.
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