Another question on throat diameter

[Wolfdog91]

So about to order some cerosafe to get some more info in my guns till I can start casting again, gonna be another moth or two before I'm set back up the way I want but I have another question. So I need to have a tight fit in my throat before I worry about my bore diameter but I'm curious. Can a rifle have such a late bore diameter it's not feasible to try and fit it tight through bullet sizeing. Say my mosin ( when I finally get around to making a electrolysis rig to properly clean the dang thing ) what if when I do my chamber cast for some unholy reason I have a bit diameter of .315 but my bor slugging shows I have a bore diameter of .312 would it just plain not be feasible to use a .315 sized bullet in that small of a bore ? Or is something like that just not gonna happen ? Or since I'm powder coating and gas chasing everything is is just a non issue? Because you know the rule I keep reading is .001-.002" larger then bore diameter. Ma ye this is more of an advanced thing but hay. So what's eveyone say

[Dutchman]

If it was me I'd resist overthinking the issue and simply try .314" cast bullets in the Mosin-Nagant. Lyman 314299 is one of two .314" molds I have for such rifles. While you're at it I'd suggest you also load some .311" and .312" cast just to see what your rifle will do. You may be surprised and will have saved yourself countless sleepless nights wondering.

Dutch

[samari46]

My Finn model 27 slugs out at .3115 so I use the lyman 314299 with wheel weights at .3135. My sizing die as originally received chewed up the bullets so used a .313 reamer to clean it up then polished it with different grits of silicon carbide paper. Hence the .3135 as that is how it ended up. Frank

[Larry Gibson]

As to throat fit Mosin Nagant rifle throats are a law unto themselves. Some of them have "normal", as we know them, chamber neck/throats. That is there is a step at the end of the chamber neck where the throat begins. You'll not want a bullet sized larger than the diameter of that throat step.

Other MNs, probably because of wartime exigencies of some communist arsenals, have little or no "step" at all at the front of the chamber case neck. The throat merely tapers from the outside diameter at the front of the chamber case neck to the leade (rifling). Thus, the initial entry into the throat can be quite large. It is best with those to size the bullet not more than .003 over groove diameter.

Additionally, some MN chamber necks are of such small diameter, given the thickness of the case necks, the bullet cannot be sized to fit the throat as the loaded rounds will not chamber. The combined diameter of the loaded cartridge neck will be larger than the chamber neck diameter in such cases. Sometimes the necks can be turned to allow such to chamber.

The above is simply the nature of the MN "beast"......