Mosin bore sizes

[WarPig1976]

.3105 is the surplus diameter. Something else is not right as people shot .312 all day long in Mosins. Are you seated too long? If it where me I'd be looking elsewhere. Shine a light down there and use a dental mirror to do a though inspection. Your shooting lead? Maybe you have some nasty lead fouling? Just an odd problem...

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[bob4wd]

.3105 is the surplus diameter. Something else is not right as people shot .312 all day long in Mosins. Are you seated too long? If it where me I'd be looking elsewhere. Shine a light down there and use a dental mirror to do a though inspection. Your shooting lead? Maybe you have some nasty lead fouling? Just an odd problem...

No matter how much I learn about stuff, it seems there's always one or two things that I didn't know (or forgot!) that are really important to the matter at hand. Such is the case here. i've been reloading for many years, but mainly using standard components and standard data. Am just now in the past year or two getting into the oddball stuff, like low velocity lead bullets on rifles. These larger diameter bullets are a good example of this. NO published data, other than internet, for the Mosin is for bullets other than .309 or .310, so I'm tiptoeing my way into this.
In this case, having always been taught that overall length should be pretty close to factory spec, I made sure to do exactly that. Didn't take into account that the ogive shape is blunter than fmj military rounds, so the bullet contacts the riflinglong before the round is fully chambered.
The visible bulge was because the bullet wasn't all the way into the neck, and the hard chambering was because the bullet was stopping all forward progress, not because the neck was too fat.
So Warpig, take a bow- you nailed it!
Off to the range in a couple of days with an assortment of 312, 313, and 314. And a lead sled, just in case!
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