It started out as the fact that there's no reloadable brass for 7.62X54R in Canada, so I ordered the Lapua brass from Huntington's. To extend brass life, I bought a necksizing die from RCBS as well.

Since I only have one Polish M44, brass interchanging between rifles is not a problem. I've noticed after one or two loadings, bolt will close quite tight sometimes(don't know exactly which ones of them) , but if I extract the unfired round, rotate it 90 degrees, chamber it again, the condition improves. Some will improve simply by unlocking the bolt then locks again

Interestingly, If I fired a "closed-tight" round as is, the bolt trun will be normal as I turn the bolt handle up after firing(seems like the unfit brass is fireformed to fit again)

It comes to me that something is "eccentric", or is this a common phenomenon on necksized brass? Can case tumbling process "knock" the dimensions of the brass off perfection?

The brass is not tumbled but lubed(inside case neck) when resize, expander ball is .311, bullet is 123 grain .311 FMJ from Speer
. Brass is tumbled after resize. Bore is clean, assume chamber is clean too.

Just remembered something : the Mosin-Nagants are push feeds, the extractor will have to snap into the rim when the bolt truns to lock, this could solve the part of "unlock it and lock again will loosen it". But again, some rounds will persist to have the "tight bolt" problem, while some will chamber effortlessly, even when the moment extractor snaps over the rim.

I`d suspect a out of round chamber. Tight chambering will occure after a few fireings when neck sizing also. If you have shot these cases a few times they may just need to be run through a full size die to set the shoulder back, resetting the head space.

Also, be sure that you are not setting your sizing die to collapse the shoulder--which is a fairly common occurrence with neck sizers. I usually adjust to that I am sizing only about 3/4 of the case neck length.

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