Progressive/regressive rifling

[JackAubrey]

Forgive me for asking such a silly question,but would someone be so kind as to explain the concept of progressive rifling found in some rifled muskets.I understand the lands and grooves are more pronounced at the breech and taper off somewhat near the muzzle.I fail to see the advantages of such rifling and the name.It would appear to be quite the opposite would produce superior accuracy( starting shallow and progressively becoming more substantial toward muzzle.)I would think the last thing one would want to contact the projectile would be stout rifling.And since the rifling is diminishing as the missile goes amuzzle I should think it would be named regressive rifling.I have oft wondered on this.Best regaeds,J.A. :hatsoff:

 

[Wes/Tex]

Usually, 'progressive' rifling not only indicates rifling changing in depth but also in rate of twist. The rifling is cut deeper at the breech and gradually becomes shallower toward the muzzle but the rate of twist speeds up as the rifling is cut toward the muzzle as well. The idea, as explained to me, was that the deeper rifling got a better hold of the patched ball (or Minie ball in the military version) and prevented either projectile type from stripping from the faster twist up front. While this theory sounds O.K. from the Minie point of view, I'm not sure how the advantage kicked in for patched balls. The Pietta made "shooters" version of the M.1858 Remington revolver uses this type rifling and has won international competitions shooting round balls. Admittedly, there is a difference between patched balls in single shot weapons adn bare balls in a revolver but the rifling seems to work. My personal opinion is that it's a good system that may not be worth the added cost unless it works with some serious competition.

 

[Toomuch_36]

Wes Tex has it about right. I have seen a few "gain twist" rifles come through the shop as well from some of the more serious competition shooters. The rifling will start out slow to get a good grip on the ball and speed up towards the muzzle. This type of rifled barrel is a bit more costly to produce, and though it produces excelent results unless you plan on joining the ranks of the realy serious "blood shooters" may not be worth the extra bucks. This would be a choice you would have to make for yourself.

Toomuch
..........
Shoot Flint

 

[Bobby Cunningham]

You have some real good Info allready I just wanted to add this their are some 20MM Vulcan Bbls floating around that are being cut in 1/2 and made in to Smoke poles these have a progressive twist, the back 1/2 works for this but the rest is two fast of twist to be of any use, unless you build a wall gun out of the entire Bbrl.

 

[paulvallandigham]

The change in depth of the rifling adds " choke " to the projectile, making it more likely that gases will be sealed behind the projectile. The gain in rate of twist was intended to slowly increase the spin to the ball or bullet so that the lead would not " strip" in the rifling by being started out at such a high rate of spin. All this seemed to work when we only had pure lead ball and bullets. With the advent of alloys, paper and copper jackets, etc, and the invention of chronographs, it now appears that gain twist has little effect on accuracy, that the lead does not " strip ", as was feared, and that there are much better ways to seal the gases than using choke in guns firing single projectiles. ( An over powder wad does the trick).

 

Where might one find and or purchase one of these 20 mm barrels? Bob

 

[John Taylor]

In the book about Pope barrels it talks about making the bore with a slight choke that runs the full length. Pope used 31 plug gauges for a 30 inch barrel so he could check each inch of the bore and "scraped" the rifling insted of using a cutter. He did shoot some very good groops with his 32-40 loading it with paper patched bullets from the muzzle, cartridge with powder was loaded from the other end.
I don't believe in gain twist barrel. I know some shooters think they are great but I'm still not sold on the idea. When the gun is fired the ball/bullet is starting from a standstill and increases volocity as it goes down the bore. With a standard twist rifling the ball will increase spin as it increases volocity. With a gain twist the ball/bullet need to increase spin faster than it increases volocity making it harder for the rifling to grip the patch or bullet. This is my 2 cents worth.
lonesomebob, send me an e-mail about a 20MM barrel. [email protected]

 

[Slamfire]

The Italians probably have the machinery just lyin' around. They used gain twist barrels in their Carcano Rifles from the time they were adopted until the final WWII model, when it was dropped for conventional rifling. I have shot both and danged if I can tell the difference. Maybe one of those premier shooters could. :hatsoff:

 

[arcticap]

From what I can gather, the breech end of the barrel starts out with a rather slow twist so the projectile won't be apt to slip the rifling as it gains velocity. The progressively faster rate of twist adds additional stabilizing energy to the projectile by increasing the spin rate, while the choked bore also contributes to increased velocity and further aids to keep the projectile from slipping. Thus, imparting more overall energy to the projectile and creating potentially longer range accuracy, at least in theory.
The important factor I guess, would be to not create a progressive rifling twist which would be too fast for the particular projectile, or it's trajectory might suffer rather than be enhanced.

One interesting antecdote from a machinist's forum reads:
"dan;
there is and always has been a controversy over gain twist VS constant twist.

my own personal opinion, and ive come to this after picking Bill Larges brain for hours, is that a properly cut barrel if straight and with a tight fitting patch for the 4" closest to the muzzle is more accurate than the guy shooting it.

Bill won the 1934, i believe, national shoot using a .35 cal. rifle and his spread was .370" which was a mean deviation of .010" on 2 shots. this was a chunk gun shoot 60 yrs. shaded open sights over a log, like in Sgt. York with Gary Cooper. i have seen the target and that was some fine shooting.

Bill didnt cut gain twist but he did refresh them back in the 30's and 40's. when i met him in the early '70s he was busier than a one legged man in a butt kicking contest.

any way the gain twist barrels that ive ever headr of started out real slow around 1:96" or 1:72" and ended around 1:48".

i do know that 1:66" was the twist that Bill used to hand cut his premium barrels but he also had several Pratt & Whitney's for 1:48" for .45 cal and smaller...jim
[url] http://www.practicalmachinist.com/ubb/ultimatebb.php/topic/13/2115.html[/url]

I also happened to read that progressive twist rate barrels are quite popular among paintball gun shooters, and shooting paintballs is somewhat similiar to shooting PRB's. They sure don't like their paintballs to burst inside their barrels.

 

[JackAubrey]

I appreciate all the replies,quite informative.I gather there is a difference of opinion on the benefits of progressive rifling and gain spin rifling.I was once told the Armi Sport 1861 Springfield has progressive rifling.It does appear rather shallow at the muzzle.Has anyone heard likewise?Jack

 

[musketshooter]

It seems that most of you are confusing progressive gain twist rifling and progressive depth rifling. CW muskets have constant 1 in 72 twist rifling. Italian rifles all have gain twist rifling (remember, they lost the war-poor firearms). CW muskets have progressive depth bores. The muzzle is tighter than the breech end. The intent is that the skirt on the musket ball "blows out" to engage the rifling in the breech and then as it goes down the bore, the "choke" in it keeps the bullet engaged in the rifling as it compresses the skirt. Great idea and it sure works.

 

[CoyoteJoe]

Thanks Musketshooter, you are right on and saved me the trouble of trying to figure out how to explain it. Progressive rifling and gain twist are two totally different critters, though one barrel could use both features. Cutting a gain twist is appearantly no big deal since Numrich Arms use to offer gain or straight for the same price.