Carcano Cav Carbine with Cruise Missile Keyholes

[Doble Troble]

They drop at 0.270 and I run them through a sizer die of the same size (that I got from Buffalo Arms). They're gas checked and lubed with Lars' BAC (love that stuff).

First I tried 10 gr of Unique = Keyholes. Today tried 19 gr 4198 = Keyholes.

Then the unappreciated genius who gave me the rifle (probably because he knew that it would be fun to watch me try to get it to shoot) crudely snipped about 1/2" off the bullets on a few of the 19 gr 4198 loads with wire cutters = no more keyholes. Accuracy seemed reasonable too.

I'm thinking that if I can shoot these things fast enough that they might stabilize. I estimate (from Quickload) that 19 gr of 4198 is probably good for 1550 fps with these arrow-like bullets. I think I can load it up to a bit over 24 gr keeping it within pressure spec, which should give ~ 1900 fps. The bore so far has been clean - no leading.

Will 1900 fps be enough?

I like 4198 because it burns in this short bbl, and I've had best accuracy with it in an Argie carbine and an FR-8.

Alternatively, I suppose I could turn down bullets on the lathe - but I like this long legged sexy bullet.

[leadhead]

I shoot that boolit in my carcano's and have no keyholing at 50 yds.
Load is 13.5 - 14.5 grs of 2400. They shoot good even in my 91/24
with the cut off barrel.
Denny

[Doble Troble]

Well, damn! 14.5 g 2400 should produce about the same velocity as 19 gr 4198. Maybe I'm close? Maybe I'll load groups of 3 up at 20, 21, 22, 23 and 24 grains.

If those loads don't work it'll be time to start working on finding a mold for 0.270" bullets that are ~ 120 -130 gr.

[303Guy]

I have some good news and some bad news. Driving a bullet faster will indeed increase its stability - that's the good news. The bad news is that you need to drive them to about 4000fps to notice the difference! No, actually, I'm being serious. Supersonic requires a tad less twist rate than subsonic and above 3500fps, even less - by just a tad!

If shortening the boolit by cutting off the tip makes it 'stabilize' would indicate the bore-ride section is too small/too long and that by shortening it there is enough rifling engagement to spin the boolit without shearing the rifling impression. In short, the cruise missile could be slipping in the rifling. By cutting off the tip, the driving bands have less shear load on them and could be surviving the trip down the bore.

[Spudgunr]

303, cutting off the tip making it stabilize wouldn't only indicate slipping in the bore. After all, the needed twist is directly related to bullet length, so it sounds to me like the guy is just shortening the bullet to a length the current twist will stabilize.

Doble, can you recover a bullet and check the rifling to see how it looks? If it is sharp, then you pretty much need to get a different bullet, if what 303 says is right about the speed only playing a marginal part.

Keep in mind if you start playing with it and it stops keyholing that it MAY be related to the weather. If thats the case, come next fall/winter it may start keyholing again due to the denser air.

[JIMinPHX]

Carcanos have gain twist rifling. The twist rate gets faster as you get closer to the muzzle. When they made the carbines, they cut the muzzle end off the longer rifle & lost the fastest part of the twist. The slower twist will require shorter boolits to stabilize properly. Gearnasher had taken a cruise missile mold & cut it down to give him a shorter boolit. You may want to consider something like that.

[JeffinNZ]

JIM: Not all Carcanos have gain twist. My FAT41 doesn't. I shoot the cruise missile in it and get oval holes but VERY good groups at 100m, eg: 2 MOA.

I am not sure that the yaw is a factor of velocity or rate of twist. If the bullets were not stable they would be side ways long before 100m IMHO. I reckon it's a factor of the throat. My bullets are sized to match the throat and the bolt takes a bit of turning down. Thing is the nose of the CM is under throat size, the first band and a half 'engrave' and then the back of the bullet is unsupported when the case neck 'gives'. My 1 1/2 driving bands of engagement go from being a support to a pivot. I believe my bullets cant in the throat and that's where the wobbly bottom is coming from.

[Doble Troble]

Thanks for the input, guys. It's a 91/38 made in Gardone Val Trompia during Fascist year XIX. From what I've read, it should be gain twist. I don't know if it was reworked and cut down.

Maybe I'll just load up a few at max and see what happens. If they keyhole, I'll start thinking about milling the base of the mold. I'll have to drill it to gas check diameter too (and drill and tap for the sprue plate.

If it just shot it wouldn't be much fun.

This is the first Carcano that I've ever laid hands on. I was expecting an example of crude engineering. Compared to the Moisins I have, it's a beautifully finished jewel. But those MNs can be very accurate, so beauty is relative.

[MtGun44]

If you have a cut down rifle that was originally gain twist you may be in deep kimshee
since the last part of the barrel (which may no longer "be in a position to contribute") is
the fast twist portion.

If so, you need a shorter boolit.

Bill

[Doble Troble]

I stumbled into a bit more info on the cut-down Carcanos. Apparently these are the 91/28 carbines that were cut down from 91 rifles.

My 91/38 should be the standard gain twist designed to stabilize 160 gr RN.

I got the info from http://personal.stevens.edu/~gliberat/carcano/