Evidently, breaking the seal between the bullet and mouth of old, stored cartridges really does improve groups. I had some Lake City '69 M2 30-06 ammo to shoot up in my US M1 Rifle. This ammo was grouping 4" at 100 yds. I pulled 20 rounds and re-seated the bullets .020" off the lands of my rifle. The groups tightened up to 2" at 100 yards. I next tried using the seater to just break the seal, by seating just a tad deeper. I could hear an audible "snick" as I eased down on the bullet. I fired that batch and got 3" groups. I am concluding that although I knew that reseating closer to the lands would improve groups, I did not know that simply breaking the seal will also improve groups. Has anyone else observed this phenomena?

Some of this old military ammo is very heavily stuck to the neck.....so much so that many collet type bullet pullers will not pull the bullets out.

Breaking the bullet loose so that there's greater uniformity of the ignition stage of firing makes great sense to me........Now try this.....break the bullet loose by seating deeper and then pull the bullet and dump the powder out. Using a phosphor bronze brush polish the inside of the case necks and resize the case to remove the military crimp without removing the primer and reinstall the powder and reseat the bullets to the very same depth as originally loaded. I'll hazard a guess that you'll see the same 2" groups as you had loading the bullet .02 from the lands.

Another thing to think about is that the bullets in the military ammo might not be seated very consistantly straight- I've heard of severe runout on some years of M2 ball ammo. Pulling the bullets and reseating them might straighten them out enough to make marked improvements in accuracy.

Ive tried alot of the same things recently with some surplus 7.62x54r, which before my mosin nagant was getting 4 to 5 inch groups at 100 yards but trying all that other stuff I manage to tighten the groups to 3 inches. Something else I tried was I took 10 shells and measured the grain weight of the powder charge and took the average and evenly reloaded the 10 cases with the same charge weight backed off 1 grain from the average. Now I am getting about 1 inch groups. It was fun to do but personally a little to much work to get bench rest accuracy from ammo that was more then likely designed to be machine gun ammo. The ammo I used was 1960's Czech manufactured silver tip FMJ 148 grain LPS cartridges.

I've done roughly the same thing with Turkish 8x57 ammo to the same effect. Now I just shoot it the way it is because its so darn cheap that it really doesn't matter to me much.

Just picked up a nice 91/30 the other day along with 440 rds of ammo for it that I'm going to play with on Friday

I custom reloaded some of that Turk 8mmMauser ammo also. Admittedly you have to enjoy doing the work at the bench, but the rewards are there. I never worry about the corrosive ammo, because I only fire the corrosive stuff in bolt rifles and clean up at the range, before the rifle even cools.
The absolute best that I have reloaded, in terms of milsurp ammo, was the Malaysian .223Rem. By just pulling the bullet and reducing the load 1/2gr to get each cartridge absolutely even in charge, and then reseating the bullet .020" off the lands of my rifle bore, I produced excellent varmint cartridges. The only way to make them better, was to substitute 55gr VMax for the 55gr fmj bullet. Prairie dogs explode real good, when hit with those VMax.

I have a Russian M44 Mosin nagant I got for 60 dollars its in excellent condition at the store I bought it from I watched them crack open the wooden crate and handed the rifle to me still wrapped in the arsenal paper.

That Czech silver tip ammo is mild corrosive due to salt in the priming but for $1.60 per 20 rounds I will not complain. as soon as I am done shooting I swab the barrel good with hoppes #9 solvent and spray the action and bolt with rem oil, then give it a thorough cleaning when I get home.