Nobody's that good with a Mosin-Nagant. I have three of them: A full-length 91/30, an M44 carbine, and an M38 carbine. The 91/30 having a longer barrel, was the most commonly-used as a sniper rifle during WW2, when it was scoped.
Mine aren't scoped and the best they can possibly do is a 4" group at 100 yards, from a sandbag rest. Even with a scoped 91/30, hitting a 3" diameter object at 100 yards is "iffy."
Hell, I have a sporterized P-1917 Enfield 30-06 with a 40mm mil-dot scope and handloads tailored for that rifle and all I can get are 1" groups at that range. What you need for that kind of accuracy is something in .556mm or .223.
I hear you on the Mosin and agree, however have a "mosin" exception. Sorta

1944 matching #'s Sako built M39. Captured from Russians, as 91/30's, Finns rebuilt them and
DID THEY! What a rifle. It's shamed many a people in turkey shoots. In one I came out 2nd of 10 and not the only one. It was a 200 meter SCOPED, offhand event. Woodchucks, 3 of them. They were about regular shoe box lid sized heavy steel. They laughed when I paid my $$ and got in the shoot, but half walked away and left when I was done. I was beat by the Sheriffs dept SGT with a scoped PSG1
Here's his....
Here's mine.... (stock photo but is a 1944 Sako)
He got 3, I got 2 during the shootoff cause we were tied at 2. Damn that was a fun shoot that year. Next year he still remembered me cause he asked me "how did you hit them at 200 meters with open sights"??? I told him "see that huge front sight? I cover the target with it, close my eyes and yank the trigger" He about died cracking up. He nicknamed me "yank the trigger"