Progressive rifelings?


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stillstanding
October 2, 2006, 11:43 PM
I've never had a custom rifle put together before and have been wondering if it would be advantagious to have maybe 30 inches of barrel rifled starting at about 1/14 and ending at about 1/10 or 1/9. I intend to rebarrel Rem 700 7mm RUM to 300 RUM and load 165 to 180 grain bullets for distance. Also, any recommendations on a dependable custom barrel maker.

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ogree
October 3, 2006, 02:42 AM
what you are referring to is called ďgain twistĒ and I donít know of any barrel makers who currently manufacture barrels this way, itís too much of a pain to get set up for it so manufacturers donít bother. A 10 twist would probably suit your needs and as far as manufacturers go, you will probably get a good number of suggestions from people on the board. I prefer Schneider barrels.

BigFatKen
October 3, 2006, 08:03 AM
Someone tried this with great hoopla a hundred years ago. He was a genius until some wiseguy installed one backwards and it shot the same. I like Schleen (sp?) barrels. Watch their video.

db_tanker
October 3, 2006, 11:38 AM
I thought Smith and Wesson was making their 460 S&W's with the progressive "gain twist" barrel?


D

JesseL
October 3, 2006, 11:43 AM
Gain twist is still used in a few special circumstances.

The new S&W 460XVRs use gain twist rifling to prevent the bullet from stripping on the lands. I would guess this is necessary because the bullet in these has already got enough velocity by the time its gotten out of the cylinder and through the forcing cone that hitting the full twist rifling would be too abrupt. Not really an issue for rifles.

I also heard about somebody making M4 barrels that had polygonal gain twist rifling in an attemt to get more velocity out of the short barrel, but I haven't head how that worked out.

DogBonz
October 3, 2006, 12:11 PM
I thought Smith and Wesson was making their 460 S&W's with the progressive "gain twist" barrel?

That is correct, sir!

Speaking of the 460, wouldn't that make a great lever gun?

stillstanding
October 3, 2006, 07:50 PM
Gain twist is the term I was looking for. It makes sense that in a rifle burning slow powder the bullet leaves the chamber more slowly than in something like the 460XVR. I think I'll give up on that train of thought. And yes I do think the 460 cartridge would do well in levered carbine or such.

Thanks for the feedback.

db_tanker
October 4, 2006, 06:51 AM
I haven't seen any tests on that cartridge on a longer barrel, but I could only imagine what your #'s would be out of a 16-18 inch rifle...considering the crazy velocities they are getting out of the handgun length barrels...plus a closed chamber...ugh...the bullets would have to be solids because I don't think there is a 451-452 dia bullet with a thick enough jacket to take that...even a true Casull bullet would be hard pressed not to seperate or simply go varmint...


Sounds like fun. :)

D

Khornet
October 4, 2006, 12:55 PM
in the American Rifleman, they showed by physics formulae why 'stripping' or jumping the lands isn't possible. Something to do with angular momentum or angular inertia of a bullet being too low to resist turning no matter how hard you drive it.

jbharned
October 4, 2006, 01:14 PM
I think the recoilless rifle and some big navy guns / artillery used gain twist also.
Easier on the driving band on the projo.I cant remember but I think the recoilless had a rifling engraved section on the driving band that was lined up when chambering.

JesseL
October 4, 2006, 01:30 PM
in the American Rifleman, they showed by physics formulae why 'stripping' or jumping the lands isn't possible. Something to do with angular momentum or angular inertia of a bullet being too low to resist turning no matter how hard you drive it.

I remember hearing about scientists 'proving' that it was physicaly immposible for bees to fly too.

Did the guys at American Rifleman figure on bullets that were already moving a few hundred fps when they hit the rifling? Or were they just assuming that the bullets would always be seated right next to the rifling when they were fired?

I'm sure S&W isn't spending the money to build gain twist barrels for the 460s just for kicks.

Khornet
October 4, 2006, 02:56 PM
we don't know whether the bee story is an urban myth, none of us having seen the math.

Second, gain twist might have other uses than preventing stripping. Like maybe reducing recoil, or the amount of torque the gun exerts on the hand.

Third, I DID see the math.

Fourth, unless the bullet is very short, it has not yet left, or barely left, the case. Therefore it would be no different than a rifle chamber, AND if it's already free of the case, some of the gases are being vented through the cylinder gap, unlike a rifle (which is, I believe, what the calculations were done on).

JesseL
October 4, 2006, 04:02 PM
we don't know whether the bee story is an urban myth, none of us having seen the math.

True. But the point stands. IIRC it was supposedly based on assumptions (which were valid for airplane designs of the time) about the lifting capacity of a given wing area. Those assumtions didn't apply. Similar mistakes happen in real life all the time.

Second, gain twist might have other uses than preventing stripping. Like maybe reducing recoil, or the amount of torque the gun exerts on the hand.

True, it very well might have other purposes. All my statements have been my own speculation, but I think they may have some validity.

Fourth, unless the bullet is very short, it has not yet left, or barely left, the case. Therefore it would be no different than a rifle chamber, AND if it's already free of the case, some of the gases are being vented through the cylinder gap, unlike a rifle (which is, I believe, what the calculations were done on).

In a rifle the bullet is near enough to the rifling that the nose of the bullet will often protrude into the rifled portion of the barrel. I don't see that happening with a revolver. Also remember that this revolver is intended to shoot .454 Casull and .45 Colt in addition to .460 S&W Mag. Those are going to sit even further back from the rifling and the 454 isn't exactly a low velocity round either.

Some evidence of the validity this premise is the fact that in shotguns shooting slugs with rifled chokes, it is common for the slug to skid on the rifling because of its velocity at the time it hits the rifling.

Iron bottom
October 4, 2006, 06:12 PM
Wil Schuemann makes gain twist barrels (the AET)for the 1911. His site has information on several things of interest to shooters.

BigFatKen
October 7, 2006, 08:52 AM
A substantial portion of total gunpowder energy goes into twisting the bullet. Gain twist may therefore gain some velocity.

Tank anti-tank rounds are now kenitic energy, sub-caliber, saboted with fins through a smooth bore. I'm not sure if they are balistic or guided'; ikeky depends.

FIFTYGUY
October 19, 2006, 11:18 PM
Progressive twist is the technical term, "GainTwist" is also a trademark.

BTW,

The GainTwist Barrel Company
113 W Yellowstone Ave
Cody, WY
(307)587-4914
(307)527-6097 fax

still makes these types of barrels.

1. I can say with certainty the US 57mm Recoilless does not have a gain twist barrel (at least mine doesn't). As has been pointed out, most US recoilless rifles use projos with pre-engraved rotating bands for technical internal ballistics reasons. Yes, you have to line up the projos with the rifling when you laod the guns. For reference, the M18/A1 57mm Recoilless Rifle has a twist of 1:67.2". And the guns are designed to counter any torque reaction from imparting spin to the projos, hence they are "twistless" to the shooter as well as recoilless.

2. How much powder energy goes into rotating a projo? Do the math:

.50 BMG, 3000 fps, 1:15" twist, 700 grain projo.
Muzzle energy (kinetic energy in direction of travel) = 14,000 ft-lbs.
Rate of rotation at muzzle works out to 144,000 rpm.

We need to know the rotational inertia, but I'll simplify and assume that the projo is a perfect cylinder. Since its mass distribution is actually much closer to the rotational axis, this should be a close or conservative estimate (real projo rotational energy would be lower than this estimate).

Still working in the awkward Imperial units:
Mass of Projo = .0031 Slugs(no pun intended!!), Rotational Inertia = 7.3 x 10e-6 Slug-Square Feet.
Kinetic Energy of Rotation = 83 ft-lbs.

So the rotational energy of a projo, in this case, is about 1/2 a percent of its linear kinetic energy. And since perhaps 25-30% of the powder energy actually goes into the final linear kinetic energy of the projo (stoichiometric efficiency), I wouldn't call about one-thousandth a "substantial portion of the total gunpowder energy".

3. Yes, other military guns *do* use gain twist rifling. The 20mm Vulcan ends up at 1:20". The 40mm Bofors L/60 goes from 1:45" to 1:30". My Vulcan and Bofors barrels look kinda weird when you gaze down the bore, almost dizzying... I seem to recall bigger arty may use gain twist as well.

4. I believe the main advantages of using gain twist may be:

-reduced chamber pressure, from reduced projo start force from trying to make it instantly fit into twisting rifling

-less stress on the rotating band

-perhaps easier to manufacture twist that's constantly increasing, instead of worrying about backlash in the barrel rifling equipment causing the rifling twist to "drift"? This kind of drift may contribute to projo "balloting" as it "rattles" axially. Better to keep a rotational force constantly in the same direction?

5. Certain revolver cannons used smooth bores, with the only rifled portion a small insert just ahead of the cylinder. The smooth bore flattened down the flanged rotating band, to streamline the projo (much like Probert rifling). See the original Marquardt 20mm cannon, which evolved into a more conventional design (the Mk 11). I have a round of original Marquardt 20mm ammo, the wide projo flange also helped keep the round's case neck from crushing forward as it was rammed into the cylinder during the loading cycle.

-Phil

rockstar.esq
October 19, 2006, 11:35 PM
This reminds me of an article I read in Rifle Reloader where they reprinted the findings of a writer who started with a 30" Springfield 06 in 30-06. The author charted the velocity differences of I think it was five different loadings as he trimmed one inch off the barrel each iteration until he got to a 12" barrel! The origninal test was done circa 1950 before the short barrel laws so I'll answer those questions before they start. The final results were interesting. Overall the trend is that velocity lowers as barrel length decreases. There were however occassions where a given loading actually gained velocity when the barrel was shortened by an inch! If I remember the data correctly the main finding was that there is no constant velocity deduction for a reduction in barrel length. I know this is a little off the topic however I though it relavent given the early comment regarding how mounting the progressively rifled barrel backwards netted the same result. I suffered through Physics for scientists and engineers and the only lasting scars from that class revolve around projectile motion. The staggering amount of information that is assumed when these calculations are made is without a doubt the reason there's so many ways to "skin a cat".

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