Question on a new term I discovered step rifling

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Question on a new term I discovered step rifling

Post by Precision » Sat Nov 14, 2020 6:41 pm

According to the guy who invented / patented his version of step rifling

At first glance, the 260 Terminator looks like a 260 Ackley Improved (AI) with a different name, but the key difference lies in the +P throat design.

Patented by Shawn Carlock, the +P throat uses stepped rifling at the throat to change where peak pressure occurs while maintaining precision. Think of it as a running start for the bullet. As the bullet leaves the case it’s supported by a shallow section of rifling. This shallow section allows the bullet to be partially engraved and supported before reaching peak chamber pressure and slamming into the full-profile rifling. By experimenting with the depth and length of this step, an ideal balance of velocity potential and accuracy can be reached. I won’t profess to know everything about the concept, but I can tell you that it works very well. A side benefit seems to be less sensitivity to bullet seating depth and concentricity while handloading. The two previous +P throated rifles I’ve worked with were very easy to load for. This one is, too.
The whole article buy a gun writer. ... al-review/

I don't really understand how this might work and how it might make for +P of a rifle cartridge. It also seems like it would increase the effect of throat erosion for the initial baby rifling portion.

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Re: Question on a new term I discovered step rifling

Post by BDK » Sat Nov 14, 2020 10:54 pm

I think I people have been experimenting with progressive rifling for years. I suppose better computer modeling might get it to work.

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Re: Question on a new term I discovered step rifling

Post by HTRN » Sat Nov 14, 2020 11:23 pm

It's a solution in search of a problem. Shallow angle lease in the throat sounds like it does the same thing, with none of the nonsense this setup involves

As for gain twist, it works decently with black powder rifles shooting cast lead, usually muzzle loaders shooting minor balls, but it seems to have no advantage with smokeless powder cartridge rifles shooting copper jacketed lead, and has the issue of limited ways to achieve the effect - you can't do it with rifling button for example.
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Re: Question on a new term I discovered step rifling

Post by toad » Sun Nov 15, 2020 6:54 am

The Germans used it for Tank guns . Various versions of the 88 mm and 75 mm guns. Sometimes called "Progressive" rifling . It was considered to expensive for small arms , the gain wasn't worth the cost. IIRC it was used on some custom double rifles.

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Re: Question on a new term I discovered step rifling

Post by Vonz90 » Fri Nov 20, 2020 10:48 pm

The M91 Carcano used progressive rifling. I am sure there were others.

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