Whacked off Carcano? Twist rates? Headaches?

Okay, so this thread isn’t about a gun in my safe, but it’s a question that I’ve never found an answer to, so I thought I’d pose it to CB…
For all those “gain twist” Carcanos out there that got Bubba’d and their barrels cut down, thus eliminating the faster twist in the gain twist, what can be done to shoot them? Is it an annoyingly light boolit? An annoyingly heavy boolit? Keep the velocity down?

Add to all this the seemingly wide range of twist rates we encounter - a 45 ACP at 1:16 shooting the projectile equivalent of a baseball or a 444 Marlin and it’s old 1:20 or 1:38 twist shooting a slightly elongated baseball, but then we’ve got a AR zipping out a pill at 1:7 and a 22/250 shooting the same pill - a bit faster - at 1:12.

I fundamentally understand rifling and twist rates, but my little brain struggles mightily when we start to talk about how this speed of twist will stabilize this bullet/boolit and this one won’t, or this caliber and this twist will stabilize the bullet/boolit and this caliber, the same twist is a recipe for disaster. And then there’s the overall weight and length of the projectile, which REALLY makes my head hurt. I’ve seen there are several formulas to calculate this stuff, too, both in terms of the size/weight of the projectile in order to stabilize it (the lowest RPM needed to get it to fly right) and the highest velocity (and thus RPM) it can structurally withstand.

Ultimately, the “Carcano” example is merely a common one we might have run into in the military guns, but I think it’s a good illustration of what I’m trying to ask. An equally useful one in the modern era is the fascination with the heavy-for-caliber (and thus “longer”) subsonic. boolits, which are fun to shoot, but again, the twist rate seemingly dictates what can and cannot be done in respect to boolit weight, yet the VLD series of target bullets (Berger, for example) run long bullets and conventional weights (up to a point) and performance is - seemingly - sublime.

Is there an easy way to think of all this - and actually remember it?

I need to go lay down now…

Cree

Its not only the twist rate, velocity also plays a big part in the bullets stabilizing. This is why a 22 hornet is limeted to 40-45 grn slugs in a 14 twist barrel but the same barrel chambered in 220 swift will do a 55-60 grn bullet. the hornets 2450 fps dosnt generate the same rpms as the swifts 4000 fps.
Then to really get confusing everyone refers to weight stabilized when it is length of the bullet stabilized. A short round nosed bullet will stabilize quicker than a long vld style in the same weight. Example is a 105 grn round nose in 243 will stabilize ina 10 twist but the same 105 boatail vld thats 1.300" long requires a 7-8 twist

It's an interesting question. I've never heard about cutting the barrels down on Carcanos with gain twist rifling as causing an accuracy problem, but have no personal experience with the problem. One might note that between the World Wars shorter versions of the rifle became more into use, such as the M-38, and they are about the right length for a sporter as-is. Also, during WW II the standard Carcano Infantry rifle was produced with regular rifling. But I do not have an answer for your exact question.

DG

Quote:

---

Originally Posted by Der Gebirgsjager

It's an interesting question. I've never heard about cutting the barrels down on Carcanos with gain twist rifling as causing an accuracy problem, but have no personal experience with the problem. One might note that between the World Wars shorter versions of the rifle became more into use, such as the M-38, and they are about the right length for a sporter as-is. Also, during WW II the standard Carcano Infantry rifle was produced with regular rifling. But I do not have an answer for your exact question.

DG

---

The answer is load and shoot it instead of talking about it.
Try and try again to make sure.

No body that I ever knew ever had much love, or got much accuracy out of these guns.
Probably the gain twist?
I have a buddy who says he can hit a barn with is, as long as he is inside and all the doors are shut.
When they were really cheap, I thought re barreling one to a 38 or 357, single shot would be fun.
Plenty of production made rifles in these cartridges on the market now, so it is pointless.

The rate of a gain twist M91 Carcano is I believe 1-19 to 1-8 at the muzzle.
By shortening the barrel and removing the fast twist, you basically destroy the accuracy.
ukrifleman

If memory serves, I think at some point they quit using gain twist in them.

FWIW. One of my brothers has one that is extremely accurate. He bought it keep out in the machine shed, but decided it was to good of a shooter for that.

The 1/8 twist is to stabilize long bullets to mile plus ranges .......using shorter/lighter bullets should compensate for the twist alteration..........as is well known ,most Carcanos are considerably oversize for 264 bullets,and that is where inaccuracy comes from.

Hornady made a bullet run once a year for the gifts from El Duce. They were .267 and 160 grain. I have a couple of large boxes. I use them in my 6.5 Grendel Subsonic AR.
You need to slug that rifle barrel to see exactly what diameter the grooves are. Plus you need to check the crown, most home brew cut-offs I have seen, never came near being even square or close to properly crowned, they shoot groups like a shotgun. Bubbaed is a complement.

Ive seen two Carcano's in 45 years. One fired J bullets reasonably well. Neither fired cast fo beans. My guess?? The cast were not fat enough.
There are custom mfgr's now that didn't exist years ago. You can get fatter boolits now.

Shiloh

The bullet diameter of Italian military ball is .266 not .264.
I have had good results with a Lee Cruise missile bullet, cut down to 150gn with a diameter of .2695.Attachment 311972
ukrifleman

Thanks for the insight, guys. Like I said in the original post, this wasn’t so much about the Carcanos themselves, more about the twist rates in general and how that impacts or affects what bullet or boolit can be stabilized (and presumably) and shot accurately. Carcanos are a great example, since the gain twist - and Bubba - can be impacted by Bubba’s hacksaw and not fitting a new barrel.

The point of the question was really based around two assumptions 1.) the projectile fit the bore properly and 2.) it was of a suitable weight. With those two points, how does the twist rate impact the accuracy?

For example - as I understand it, my 358 has a 1:16, which I’ve read should make stabilizing long (and heavier) projectiles more difficult, on the other hand, my .308 is a 1:12, and as I understand it, that “slower” rate makes it easier to stabilize longer and heavier. Drop down to a smaller caliber, and you’ve got faster rates across the board, but the 223 seems to want to spin a 55 grainer with no issue at 1:8, but a 22-250 seems to do better (albeit faster) with a slower twist. Then along comes a 22 Hornet and those are - what? 1:14?

Just gives me a headache, and I know there are multiple variables - bullet/boolit fit in the bore, speed, weight, length (to name a few) - but going back to a Carcano, IF someone slowed the rate of twist down (by cutting the barrel on a gain twist rifle), what is the solution to the rifle not spinning the bullet fast enough?

Or, to give another example, the much maligned Lee Cruise Missile. The consensus here is it’s simply too long for it’s own good, yet there are quite few examples of it being quite accurate in a certain velocity range.

In our Carcano example, with rifling that’s too slow because Bubba cut off the fast part of the rifling, do we go with the lightest projectile? The heaviest? Do we slow it waaaaay down? Do we pack it full of 4064 and send it?

Again, I don’t own a Carcano, I’m really just trying to better understand the impact the twist rate has on proper bullet/boolit selection (weight and length-wise).

Thanks for all your comments!

This has been a known issue for a very long time. In the mid 1920’s the Italian military took many worn M-91 long rifles and cut them into a Carbine pattern known as the M-91/24. These have been well known to be inaccurate, but evidently were good enough for the time. I have never been able to find out what the functional twist rate was for these shortened carbines. But the Italians converted nearly 250,000 of them, and used them everywhere they fought in WWII. Maybe not preferred issue, but still useful.

http://www.cruffler.com/Features/DEC...ecember01.html