Variable/Gain Twist rifling

[Ram4x4]

Anyone have, or used a barrel with gain twist rifling?  I've read some on it and understand the premise, but wondering if anyone has ever had experience with it?

One thing I often see printed is that fast twist rates, especially useful in smaller calibers with heavier bullets, is that it can raise pressures and with high speed, small calibers (like 22-250) can cause problems with the bullet jackets.

I see some of the newer VLD (Very Low Drag) bullets in .224 are as heavy as 80 or 90 grains (like the Berger 80 grain Match VLD and 90 grain HPBT VLD-Target).  Obviously these need a pretty fast twist to stabilize.  It makes sense to me that a gain twist barrel would allow lower pressures (and thus allow hotter loads to crank out the heavy bullets at higher velocities).

I can imagine a 5R gain twist for .224 that starts at something like 1:18 and ends at 1:7 or 1:8 twist to shoot a 70-80 grain boat tail varmint grenade or V-max type bullet.  I'm thinking the ballistics on such a bullet leaving the barrel at 3500 fps would be quite viable out to 800 yards or beyond.  Ballistics calculator shows way more than enough retained energy and velocity at that range to still provide "explosive" impact with the varmint bullet.  It also provides for a 350 yard MPBR (Maximum Point Blank Range) for a 3 inch target.

If I had the money, I'd have a custom barrel like that made to experiment with.

[BUGEYE]

Being an expert in only one field which doesn't include guns, I'm guessing that gain twist would be easier on the bullet.  start with less violence and gradually speed up.
but remember, I'm just guessing.

[RevJim]

 For a short time, back in 2007, I had a custom rifle with a gain twist barrel. My gunsmith had made this rifle in .338 RUM on a Howa action and an inline magazine (you opened the floor plate, dropped in two rounds and closed it) it had a a barrel that was made by a company in Kalispell, WY, but I can't remember its name, they went out of business. Anyhow, the barrel as 25" long, with a 1" in 30 to 10! Started out at 1/30 and was 1/10 at the muzzle. I was able to get the Nosler 180gr Accubond to 3500 fps! I used a case full of H4831 and Fed 215M primer. I shot a huge Aoudad ram with it near Sanderson, TX at a tad over 250yds, one shot, and down he went. The Accubond acted like Partitions, which was neat and that rifle was super flat shooting! It had one big problem for me...it was butt ugly! Had a Pepper laminate stock and it just did not appeal to me. My Outfitter, however, liked the rifle so much he offered me a ton of money for it and its Leupold 3x10, so I left it in Texas! I now wish I still had it, just because that barrel was a novelty in itself! I only have that one experience, but it was a good one! Good luck to you Pard.

[roper]

Anyone have, or used a barrel with gain twist rifling?  I've read some on it and understand the premise, but wondering if anyone has ever had experience with it?

One thing I often see printed is that fast twist rates, especially useful in smaller calibers with heavier bullets, is that it can raise pressures and with high speed, small calibers (like 22-250) can cause problems with the bullet jackets.

I see some of the newer VLD (Very Low Drag) bullets in .224 are as heavy as 80 or 90 grains (like the Berger 80 grain Match VLD and 90 grain HPBT VLD-Target).  Obviously these need a pretty fast twist to stabilize.  It makes sense to me that a gain twist barrel would allow lower pressures (and thus allow hotter loads to crank out the heavy bullets at higher velocities).

I can imagine a 5R gain twist for .224 that starts at something like 1:18 and ends at 1:7 or 1:8 twist to shoot a 70-80 grain boat tail varmint grenade or V-max type bullet.  I'm thinking the ballistics on such a bullet leaving the barrel at 3500 fps would be quite viable out to 800 yards or beyond.  Ballistics calculator shows way more than enough retained energy and velocity at that range to still provide "explosive" impact with the varmint bullet.  It also provides for a 350 yard MPBR (Maximum Point Blank Range) for a 3 inch target.

If I had the money, I'd have a custom barrel like that made to experiment with.

 

I really don't think you gain much.  Unless someone has already build rifle you want, no way to compare and good point is RevJim data for his 338 RUM.  My nephew had 338 RUM build used PacNor 1/10 twist barrel and using Nosler data with 180gr bullets he got over 3500fps and Nosler max load velocity is 3544fps. 

You might want to call Bartlein http://www.bartleinbarrels.com/Trifling.htm and ask them.

[Mikey]

Ram:  the gain twist has been used in artillery for years and is or has been used with mortars, I believe.
 
In rifles, the gain twist was most noticeably used in the Italian Carcano rifle, in both the 29 and 20" rifle and carbine.  The Carcano, known formally as the Mannlicher Carcano in 6.5x52mm used a very effective heavy for the bore bullet weighing 160 gns.  Pre-war versions of both the rifle and the carbine, made either by Terni or Beretta (??, maybe) were very well made and quite accurate.  Wartime versions used a baked on paint for protective covering and made what was otherwise a well made military rifle look like junk.  The action itself is strong enough for the 6.5mm Italian round as well as the 7.35mm Italian round, both of which perform comparatively with their comtemporaries.  Some Carcano actions were barrelled in the 8x57mm cartridge.  Many detractors of the Italian rifle and cartridge speak to weak actions, a inaccurate cartridge and many of the war-time surplus as having been dropped only once.  None are true.  There are similarities between the Carcano and the Mosin actions but overall, teh gain twist rifling used in the Carcano rifles was quite successful.
 
As to the concept that the use of a gain twist would reduce throat wear - possibly but I wouldn't be willing to go the expense of having a smaller caliber rifled in such a twist just to experiment with it. 
 
I'm also not so certain that it is the twist rate that causes pressure problems with small bore rifles as pressure decrease as the bullet moves down the bore.  I would think pressure problems are more a function of  powder and depth of bullet seating rather than twist.  jmo though.

[Catfish]

Gain twist has been around since the muzzle loading day and has never caught on. I would think that if it had any real advantage it would be popular by now.

[Ram4x4]

That's the thing.  I know gain twist has been around since the muzzle loaders and by all accounts, on modern rifles gain twist seems to be quite successful when used.  I suspect it hasn't caught on probably due to an economic concern.  Not having actually priced a custom gain twist barrel yet, I suspect the likes of Remington, Savage, Ruger, etc can't mass produce an off-the-shelf rifle with a gain twist barrel that wouldn't cost a fair bit more than a "standard" model could be had for, or at least not economical enough that they'd sell well.

Looking at the BR competition or some other long range discipline it seems the calibers and velocities those guys are using don't really show a big need for gain twist.

I'm just very intrigued by the possibilities of an 80 or 90 grain bullet in .224 caliber for long range varminting.  Since my initial post I've done more reading and it looks like gain twist works well for bullets with small contact area in the rifling, exactly what you would find with a muzzle loader and a round ball, and not so much with modern, longer bullets that have large contact areas.  However, what's interesting with the muzzle loader is that a round ball doesn't need much rotation to stabilize it.  1:72 is sufficient for round ball, hmmm.

My interest in the gain twist isn't about throat erosion at all, only to allow the charge to accelerate a long, heavy bullet easier to avoid upsetting the bullet jacket (also my desire for 5R rifling since it doesn't have lands direcly across from each other squeezing into the bullet).  The ratchet profile helps protect the bullet jacket as well from sharp edges of standard rifling and also makes cleaning easier.

There's a couple of barrel makers still offering gain twist barrels.  I might price one out to see what I can build a 22-250 on to shoot the 90 grain berger.  The idea here is something in .224 caliber that is capable of taking out pdogs at 800+ yards...just because 

I realize this would be a very cartridge/bullet combo specific rifle, which is perfectly OK if it works.

[Bugflipper]

I tried them several years ago when I was doing bench rest in a 6 ppc as an experiment. My main purpose was to shorten the case to get a compressed load, hoping to increase velocity a little and maintain accuracy. I did 3 of them. The first was with a standard length chamber, experimenting with over sami pressure rounds. The second was reduced a bit just shortening the neck on the round. The third was with the shoulder set back a little and a standard length neck. Accuracy was best with the 3rd barrel. But honestly was considerably less than I was getting with standard ppc match chambers in regular twist barrels. The only difference was I was able to get a little more velocity to fight the wind a bit. With gusts my groups would be tighter but on still days a standard barrel grouped better.


 I rechambered the 2 shorter ones to standard length. Turned one into a long range groundhog rifle. Turned another one down to make a light weight deer rifle. The 3rd one I can't remember what I did with it. Seems like I used it as a tractor gun for awhile, who knows? You can get a little more velocity out of them since the sami pressure standards for a regular twist are lower than what the initial twist is actually giving. Just a guess with no fact behind it: I figured that  it was creating more drag as the bullet went further down the barrel, increasing harmonics over what it would be in normal rifling. They were all 2" bull barrels so harmonics didn't play a whole lot, but a bad group back then would have been a 32nd bigger, so not trying to imply that they were grossly inaccurate, just trying to relate that the ones I played with weren't more accurate than standard rifling.

[Ram4x4]

Nice info, thanks.  I don't think I'm expecting better accuracy.  I'm worried what a standard barrel in a 1:8 or 1:9 twist might do to a 90 grain .224 bullet banging out at 3300+ FPS. 

I'm also trying to get an idea what sort of velocity a 22-250 case could push a 90 grainer.  I'd like to push that bullet at least 3300 fps, preferably 3500, or even higher if I can.  Want/need the retained energy at 800+ yards.  That depends on a lot of factors, so tough to figure out.  I can get a rough idea if using the 1:14 twist found on most 22-250's, but if tightening up the twist to 1:8 or 1:9 that'll change things too.

Of course, it's all just mental games at this point.  Heck, the deeper I go into it, I might even end up building up a wildcat if I need a little more case capacity.

I know there are other rounds out there that will already give me the ability to shoot that far, but that isn't the point at all.  I want to do it with a .22 bullet!  ;-P

[gypsyman]

There are several gunsmith/builders that set up at Camp Perry that use gain twist rifling in AR type rifle's. Most have pretty good luck out to the 600yd line. After that, to many variables that can affect that small .22 bullet. Some have competed at the 1000yd range, but, usually without much luck. If all your going to do is punch holes in paper, go for it. If your varmint hunting, I'm sure you'll have better luck with the 6mm/.25/ or 6.5mm bullets. I have talked with several varmint hunters, that have laid claim to 800yd and out kills on p-dogs. With .22cal rifle's, but, with several shots and Kentucky windage. gypsyman

[thesandman]

greetings Ram;  you do know that a longer bullet has more surface area to contact crosswinds. kind of like a high profile vehicle compared to a sportscar.  I think your concerns of pressure spikes at take off are minimal, as in a overbore case like 22 250 a very slow powder is used, and lite bullets dont lite the fire as efficiently.  when you change the rate of twist it changes the groove/land mark on the jacket actually increasing drag as twist increases. changing rotation speed of a bullet that is just starting to move is much easier than changing it at 3000fps.  this will cause shear in the jackets.  that is one reason why a vld bullet is designed to reduce friction/heat.  mho is that its a experiment in diminishing returns.  a simple fix to your percieved problem would be to lap a barrel to a taper reducing dia. of lands as bullet travels foward.  stability of a bullet is crutial at start up.  having recovered many bullets for inspection. a barrel doesnt fix a bullet. If it enters badly it leaves badly causing bullet to become deformed. bullet jump or freebore all play a role.  lots to think about.  good luck with project.