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PostPosted: Mon Apr 11, 2016 1:22 pm 
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Location: Tecumseh, Ontario in South Western Ontario
I have another idea - where the barrel rifling starts out at say an easy 1:30" twist rate and gradually, continuously increases the rate of twist to say 1:10". It would reduce resistance and gain a greater twist rate to stabilize the projectile. Has this been done before?
Perhaps our research guru whitewolf could find out for us.
--Ed.

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PostPosted: Mon Apr 11, 2016 1:39 pm 
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Location: P.G. B.C.
Nothing new about gain twist barrels. Used on match rifles in the 1800's and indeed, around 1900 hit their pinochle of development. There are a couple barrel makers today in the States, making them. Google - Gain Twist Rifle Barrels

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PostPosted: Mon Apr 11, 2016 1:41 pm 
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Thanks Daryl,
I'm a genius of the obvious lol.
--Ed.

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PostPosted: Mon Apr 11, 2016 3:13 pm 
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Location: Thunder Bay
Italian 6.5X53 Manlicher-Carcano has a gain twist barrel. I had one. So did Lee Harvey Oswald.

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PostPosted: Mon Apr 11, 2016 3:22 pm 
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That's interesting. I don't know what '6.5X53' means.
Was there an advantage to the gain twist in your experience?
--Ed.

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PostPosted: Mon Apr 11, 2016 3:28 pm 
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Aged wrote:
That's interesting. I don't know what '6.5X53' means.

That refers to the size of the bullet/cartridge: 6.5mm wide bullet; 53mm long case.


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PostPosted: Mon Apr 11, 2016 7:27 pm 
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Aged wrote:
That's interesting. I don't know what '6.5X53' means.
Was there an advantage to the gain twist in your experience?
--Ed.

Penage guy answered the first part of your question; here's my best guess on the second part:

Firstly, the Italian Carcano (It was 6.5X52 Mannlicher-Carcano -not53; my bad) had abysmal quality control. Probably one of the worst military rifles for conversion to a sporter, so performance wasn't something I expected. The rifle I owned was a replica of the rifle supposedly used to assassinate JFK. It had the side scope mount, cheap scope and military wood. I handloaded ammo for it since factory sporting ammo was virtually unobtainable in North America. I converted 6.5X54 Mannlicher-Schoenauer brass.

The principle behind the gain twist rifling is as you thought. Since energy from the powder combustion is also used to impart spin to the bullet, a slow twist to start allows the peak pressure provided by the burning powder to accelerate the bullet, then as the pressure starts to fall, spin is imparted to the bullet. That's the theory, anyway. Handloading powders today are more sophisticated than the powders of 100 years ago. Today's powders are much more progressive burning and build pressure slower so the gain twist is unnecessary.

Now I'm curious -While gain twist barrels are popular with the benchrest folks, are there any current production powder burners or airguns with gain twist barrels?

Cheers!

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PostPosted: Mon Apr 11, 2016 7:56 pm 
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When you change the rifling twist along the barrel, you must also change the angle of the grooves engraved on the bullet.... so they must end up fan shaped, or in the case of the FX Smooth Twist barrels, stripped....

Bob

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PostPosted: Mon Apr 11, 2016 9:34 pm 
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Yes you're right Bob I never thought of that.
--Ed.

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PostPosted: Tue Apr 12, 2016 2:16 am 
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rsterne wrote:
When you change the rifling twist along the barrel, you must also change the angle of the grooves engraved on the bullet.... so they must end up fan shaped, or in the case of the FX Smooth Twist barrels, stripped....

Bob


Thanks again Bob, for your experience!

I have been a cast bullet powder burner shooter for many years, and the idea of a smoothbore with a short rifled section at the end of it seems like one super-long freebore. Definitely not something a cast bullet can survive. In my experience, cast bullets shoot their best with the bullet seated so that it is touching or lightly engraved by the rifling when chambered. I kind of thought the idea of those FX Smooth Twist barrels would cause stripping. However, a pellet has less mass than a bullet and will require less energy to impart the necessary rotational spin. Less gripping surface on the pellet. Hardness of lead is a factor. Probably some real mind-bending math in there. Sure is interesting, and waaaay out of my league!

The Carcano had a conventional leade for a heavy (160gr) 6.5mm bullet. The twist started out at 1 in 19, increasing to 1 in 8 at the muzzle. With handloaded ammo, it was actually fairly accurate (2 moa). My rifle had a fat bore at .268, so it would shoot jacketed ammo OK, but I could not find a cast bullet mold that would cast a bullet fat enough.

Rick.

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I'm not multitasking. I'm doing something else until I remember what I was doing.


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PostPosted: Tue Apr 12, 2016 7:32 am 
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ricksplace wrote:
Less gripping surface on the pellet.

Rick.


Unlike a bullet the diablo pellet only has one small spot that seriously engages the rifling. There would have to be a length of surface area or at least two points of contact for a conflict.
Again unlike a bullet where friction isn't a big factor with all that energy the air guns velocity could benefit from a more gradually spun pellet.
--Ed

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PostPosted: Tue Apr 12, 2016 10:40 am 
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Location: Coalmont BC
The swaged-in twist rate of an FX Smooth Twist barrel, taken from photos of the mandrel in their video, is roughly 16".... The measured spin rate of the bullets after they leave the muzzle is anywhere from 40" to 13 feet (156"), depending on how hard the pellet was and who made the measurements.... Photos of recovered pellets show virtually no rifling marks, the pellets have virtually stripped through the rifled section at the muzzle, picking up only a small portion of the twist....

On another Forum, photos of a target at 262 yds. (IIRC) show the pellets impacting nearly sideways, they are starting to tumble.... which I think indicates they are running out of spin stability at long range.... At closer ranges, the ST barrels are quite accurate, although 25M benchrest shooters don't seem to be using them....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Apr 12, 2016 12:45 pm 
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Location: P.G. B.C.
Bullets meant for gain twist barrels are usually of rather short length, due to the 'skidding' and excessively wide land engraving on the bullet itself due to the twist range increase as Bob noted above.

Paradox and Rifle Choke rifles have only the last 3" or so of barrel rifled. The rifling is typically quite deep, sometimes ratchet shaped as the ball or bullet is almost at full velocity when striking the tight rifled section and must 'take' the rifling to spin for stability. These 'rifles' were quite popular, but of course are dangerous game rifles only, meant for the African Continent and perhaps India as well. Typical gauges were 12 through 8.


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PostPosted: Tue Apr 12, 2016 2:22 pm 
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Joined: Mon Aug 24, 2015 4:56 pm
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Location: Tecumseh, Ontario in South Western Ontario
Once again I'm lost with your airgunese language :) No need to explain it any further. It's no fault of you gentleman it just means I need more time on this site to learn.
BTW I love this forum and will no doubt spend that time to learn the lingo.
--Ed.

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