"Skinny" .30s in Mosin?

[mosinman]

Okay, here's the plan...

Mosin 91/30 has these dims.: bore (lands), .302; groove, .313; throat, .316

Wanted to use Lee C312-185-1R for PP boolit, but have since read several posts on this forum that nose dia. typically runs .300 to .3015

Not a huge obstacle, can get by it by "beagling" or lapping the mould, right? But if I'm going to do that, why not choose one of Lee's .309 rifle moulds from the same approx. wgt. range? Main advantage would be little or no sizing of the body portion.

Alloy is WW with a little added tin. Harder alloy is not an option.

Please post your thoughts on this. TIA ,

mosinman

[rhbrink]

I think that you will have the same problem with the nose too small, don't know for sure cause I'm not that familiar with Lee molds. Maybe someone will be along here directly that has some knowledge of Lee molds. For sure the Saeco 315 will work in my Mosin and all the bore, groove and throat dims.: are slightly larger than your rifle.
Richard
Missourians for Mosins

[Zeek]

With most modern chamberings, the throating design would make it very difficult to solve such a problem, given that the bare nose cylinder is too small to work, but you cannot build it up much at all before it is WAY too big in diameter to fit between the land-tops on chambering the round. However, such is NOT the case with your Mosin, given that its lead cone tapers at only a ~1/2 degree Basic (per side) angle. That, combined with the gentle chambermouth-to-throating transition cone angle (just 6 degrees/side, rather than the usual 45 degrees) means that the front end of the leade cone is ~1.1" ahead of the base of the neck.

This means you can patch on at least part of the cylindrical nose, as well as on the bands, and still seat it out nicely, so long as the patch is not too thick. That makes a 3X patch of 0.001" thick tracing paper (the thin kind) ideal, as it only adds ~0.006" of diameter. So, of the CBoo's bands/nose are 0.309/0.300, then adding the 0.006" patch makes them 0.315"/0.306", respectively.

If we assume that you can push the front end of the patch (on the cylindrical CBoo nose) forward until it sizes-down (in the leade cone) to ~0.304", then how far forward is that from the base of the neck, if the neck is the usual 0.335" long and the transition cone is 0.07" long? A bit of applied triggernometry indicates that this 0.304"-diameter location (in the leade cone) is 0.335 + 0.07 + 0.63 = ~1.0" forward of the base of the neck.

Therefore, if we used a 0.006" added-diameter (3X tr. paper) patch, and seated to the base of the neck, our patch, on the nose could be 1.0" ahead of the base of the PPCBoo and still chamber with minimal effort. When that round fires, the too-big-diameter nose will get crushed down and centered by the patch, whereas the far-larger-diameter drive band section will seal and give the torque-up capability needed.

Stated another way, it looks like a 1" long CBoo (with a 1/4" long point and a 3X tracing paper patch clear out to the point) would need to be seated out ~1/4" forward of the base of the neck to get a tight fit into the leade cone. If you don't like that, then use a thicker patch on both nose and bands, but know that you'll have to size down the bands a bit to have them fit into your read-of-leade-cone diameter. Still, that is not much trouble.

It looks to me as if a 3X thin-tracing-paper patch should work rather nicely for you, patched on the nose and bands, and leaving off the gas check. This would require no post-patching size-down and, if the bullet's drive bands are no larger than 0.310", would require no pre-patching size down either. That is pretty snazzy, if you ask me! The chambering's very-gentle-leade-cone-angle is what makes this sort of magic possible. Try such a trick on a 308W or 30-06 and you'll soon wish that you had not.
Enjoy,
Zeek

[rhbrink]

Well there you go!