The one thing I see is what would happen under recoil. Muzzle climb would tend to lift the rifle up, off of the cutout for the left forehoof. The trigger being at an angle, there is already some upward pressure, too. If the caliber had any recoil to speak of, the soldier would be in danger of dropping the rifle. Think of where the pivot-point is (the buttplate of the shoulder stock).To solve this, the shoulder piece must be higher. Draw a line through the barrel straight back. If the line does not pass well within the buttplate, there will be muzzle lift. Of course, this also makes it a lot harder to get a good cheek weld and sight picture, and if the sight line is well above the muzzle line (like on the AR-15, 2.6" between bore and sight) there will be serious issues with sighting the rifle for point-of-impact; any attempt to zero the point of impact at a given range will result in serious inaccuracies at any other range. This site has all sorts of graphs-and-stuff that explains why this is such an issue.The buttplate as drawn will also tend to make the rifle slip up and off the shoulder during recoil. Buttplates are vertical on real-world rifles for this reason.Mind you, if this were a .22 Long Rifle, the recoil would be trivial. You'd almost certainly be limited to calibers under 1,000 ft-lbs of muzzle energy such as the .30 Carbine or, more likely, the .38-55 Winchester . In the absence of armor, at range where instant-disabling isn't critical, and given that many deer and black bear have been taken by this cartridge, against a griffin or enemy pony that would be plenty (though with dragons... not so much). The blackpowder-fuelled .38-55 also has the advantage of being "period" for the type of weapon you're describing, hailing back to 1884, and has a reputation for accuracy, capable of minute-of-angle performance . Hey, if you're gonna shoot, might as well hit what you're shootin' at.Firearms are made of steel, walnut wood and compromise... not necessarily in that order.