Gain twist

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(Firearms) twist of which the pitch is less, and the inclination greater, at the muzzle than at the breech.

See also: Twist

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
I control pressure by using a 20" Bartlein gain twist barrel starting at 1:13 and ending at 1:6.5 at the muzzle.
AET indicates that the rifling in the barrel actually increases in twist as it nears the muzzle, otherwise known as gain twist rifling.
Lewis rifled his guns with a gain twist, and the rifling in this piece appears to be designed for a patched picket bullet rather than a round-ball.
In order to mislead the police and give the crime a "murder for gain twist", Roshan stole some gold jewellery from Saurabh's home and dumped them in a nearby lake.
For another, the Model 460XVR employs 1:100/1:20 "gain twist rifling" in the bore.
Schuemann Barrels (SCHUEMANN.COM) offers its premium M1911 barrels with either a 1:16, 1:24 or 1:32 twist and has announced its intention to eventually standardize on a 1:24 Gain Twist format.
Smith & Wesson is using this process now for quite a few of their barrels, including the gain twist used on the .500 S&W Magnum.
Gain twist starts bullet rotation slowly and speeds it up toward the muzzle, lowering pressure and enhancing extraction.
Gain twist simply means the twist of the barrel rifling becomes faster towards the muzzle.
Back in the 19th century, when rifling was cut deeper and more coarsely with tools less precise than used by gunmakers today and revolver bullets were soft-lead balls, a gain twist prevented the sharp lands and grooves from "stripping" material from the ball in the forcing cone and then merely sliding down the bore without sufficient spin.
For more information, "Gain Twist Barrels For Palma" (December 2016) covers more.