The barrel looks correct and in the same pic you can see there is no lug like a No4 has on the right side below the wood. If you turn it upside down does the trigger guard form a figure 8 at the front screw? The magazine is a force match. Around here a much worse No5 which was drilled tapped and filled with screws with a rusty bore was going for $750 so I guess $300 should be a decent price. Bill