Here's some pics ofd differences between a wartime receiver (round 1943) and a prewar hex receiver. You can definitely see that the Russians were cranking them out for function as fast as they could when the Nazis were on their door step.
1925 hex markings. Also note the machining is much smoother. This is made in the same factory as the 1943 in these pictures. Big differences in the details. Also, the bolt operates much smoother on the '25 even when I get it hot with laquer coated ammo which some people have tried to convince me will melt when it's hot and stick the bolt shut (Haven't experienced it myself with hot Mosins though after I've scrobbed the chambers completely free of cosmoline.)
Markings on a "peak of war time" 1943:
The '43 is out of the stock, because it was not properly fitted and the stock began to split resulting in 8-10 inch groups at 100 yds. After repairing, pinning, and bedding the action to the stock, groups are down to 2" with Brown Bear "Match" loads.
The Winchester Brass cased commercial ammo shoots pretty well to, but it is just rebranded Sellor & Bellot, which you can usually buy for a couple bucks less per box under the original Czech brand name. (The Winchester box says it's made in Czech Republic, and the ammo shoots the same).