A Model 1891 to keep my 1898 Krag, 1891 Mosin-Nagant and 1896 Swede company.

[RBruce]

Patrick, Since I don't have a .31" soft lead ball, I drove a .280 cast lead bullet into the muzzle. The measurements where the lead was displaced are .671mm and .696mm, lands and grooves. Can you determine the bore from these readings? If so, would standard 6.5mm bullets be likely to work in this rifle?

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[Patrick Chadwick]

Since I don't have a .31" soft lead ball, I drove a .280 cast lead bullet into the muzzle.

That's fine, as long as you managed to get it right through the barrel! If you only drove it into the muzzle and out again, then you may be measuring a worn muzzle end, and do not know if the rest of the barrel is the same or tighter.The trouble with measuring the bore is that with a 3-groove bore you do not get a clean "Over grooves" figure, as there is a land opposite each groove. I hope your rifle has a 4-groove bore, in which case the max/min diameters on the slug do indeed correspond to the groove/land diameters.

Now for the worrying bit: The CIP bore/groove dimensions are given as 6.50 / 6.80 mm for a 4-groove barrel. You have measured 6.71 and 6.96. That sounds like a badly worn barrel. So please check your measuring devices (zero on micrometer or slide gauge, for instance).
As I wrote in my previous post, if the barrel is seriously bell-mouthed, there is not much you can do about it, and the rifle will probably shoot very poorly indeed.

If, on the other hand, the barrel is worn all the way down, i.e. oversized but constant, then the situation is not hopeless, but very awkward. You will need bullets that are thicker than the standard 0.264" (6.70 mm). If your measurements are correct, then a 6.5mm bullet will slide right into the muzzle. So try exactly that. If the 6.5 /.264 does indeed slide right in and stick somewhere down the bore, then the situation is hopeless. If it slides right through, then you have 2 options for shooting a) use the Hornady .268 (6.8mm) bullet made specifically for the Carcano - if you can still find them or b) use hard cast lead bullets with a diemeter of 6.9mm. The trouble with the first option is that there will be a lot of gas blow-by, and the trouble with the second option is that the neck of a loaded cartridge may be so enlarged that the cartridge will not chamber.

Check those measurements, and get hold of a piece of lead that you can drive right through the bore!


Patrick