Progressive rifling

[Mark Thomason]

Some rifle muskets used progressive rifling, meaning by the description I found that the groove was .005 deep at the muzzle and .015 deep at the breech end. I also read that this was adopted after extensive tests of at least twenty variations at Springfield Armory for our standard Springfield rifle muskets. They were convinced it worked after trying many things. What is current opinion? Did it work?

Are there other versions of progressive rifling out there, of groove width instead of depth, or of different depths?

Was it used in breach loading firearms? This would greatly expand how often it might be encountered.

This relates to proper bullet diameter, since if groove depth varies, it cannot answer the question of bullet diameter in any of the ways that I have heard.

Slugging one end of a progressive barrel would be misleading, too.

I realize this is pretty basic stuff, and I appreciate the your help. If I don't know the basics, I can't go farther.

[MtGun44]

Italian Mannlicher-Carcano used gain-twist rifling.

Bill

[runfiverun]

iirc it is still offered as a custom bbl [from shilen maybe.]

[Wayne Smith]

Two different things. Mark is talking about progressive lessening of the depth of the rifling groove, not the speed of the twist. Gain twist is old. The original idea, as I understand it, was the initial slow twist allowed the boolit to engrave the lands without skidding, once engraved the twist could speed up without damaging the boolit. The Patterson Colt had gain twist rifling.

I'm not sure about Mark's subject. Anyone know the history?

[44man]

A problem with muzzle loaders back then was fouling in battle. It was so bad that many soldiers carried a variety of different size balls or Minnie' balls so they could still load as the bore filled. Hardly any really fit the rifling and was why the Minie' was developed. But as the grooves filled with crud, they got harder to load and rifling stopped working like it should.
Since a Minnie' was smaller then bore size I imagine the idea was to have the skirt expand into deeper rifling and as it was squeezed into less deep grooves, it would scrape out fouling. A better gas seal is a side benefit.
Now I don't know if I am right but it's the only thing that makes sense.

[44man]

Another thing that works with breech loaders is a slight choke to the bore where the whole ID gets a little tighter near the muzzle. Pedersoli uses this in their cartridge rifles to great effect.

[curator]

Mark,

I am not aware of any Springfield rifle-musket made with progressive rifling. Enfield rifled muskets, yes.

Progressive rifling was designed to provide more "grip" on the bullet as well as increase the pressure curve of the black powder charge. Enfield cartridges were loaded with about 70 grains of high quality black powder and a 530 grain Prichett or Burton Minie bullet. The progressive rifling probably results in a bit more barrel time, and enough more pressure to give a cleaner burn and significantly less fouling.

A 1853 Enfield rifle using correctly made paper cartridges could be accurately fired as many at 50 times without cleaning. This was due in part to the progressive rifling as well as the powder quality, bullet design, and bee's wax lubricant. In essence, the rifle and cartridge were a "system" designed to work with the limitations and challenges of black powder and muzzle loading technology.

In contrast, the 1863 Springfield using American contract cartridges would usually be impossible to reload after twelve or often less shots.