Rate of twist?
- Thread starter Mr.IDontKnow
- Start date
Rate of twist means how fast your rifle barrel spins a bullet before it leaves the barrrel. There are ideal twists that match bullet weight that take into consideration what you want to do with the rifle. Normally faster twist means heavier bullet.
Just to fill in a bit more, rate of twist is expressed as one complete 360 degree rotation of a point travelling along the rifling groove per X inches of barrel length, with the rotational axis being the centre of the barrel bore. So if the point rotates completely in 7 inches of barrel length (called 1-7 twist) that is considered "fast". And if the point rotates completely in 14 inches of barrel length (1-14) that is considered "slow".
To give you an idea: I own a Remington R5 with a 1-11.25 twist which is just slightly faster than the standard 1-12 twist usually found in .308 rifles. Supposedly, this difference in twist makes the rifle shoot 175 grain bullets better than it shoots 168 grain bullets, but you would have to be a better shooter than me to really tell.
Rate of twist is quite important when talking about rifles shooting .223. An older style 1-12 barrel will really only shoot the 55-grain stuff, whereas the modern 1-8 or 1-9 barrels will shoot the high-end 68 and 75-grain bullets.
To give you an idea: I own a Remington R5 with a 1-11.25 twist which is just slightly faster than the standard 1-12 twist usually found in .308 rifles. Supposedly, this difference in twist makes the rifle shoot 175 grain bullets better than it shoots 168 grain bullets, but you would have to be a better shooter than me to really tell.
Rate of twist is quite important when talking about rifles shooting .223. An older style 1-12 barrel will really only shoot the 55-grain stuff, whereas the modern 1-8 or 1-9 barrels will shoot the high-end 68 and 75-grain bullets.
Mr.IDontKnow
New member
Hmm I get it now, but will faster or slow affect my accuracy? Or it will just shoot better bullets with different grain?
Greener has a formula, at least a century old, that calculates the optimal twist for bullet diameter, muzzle velocity, and shape. All else being equal - seldom the case but still - a bullet fired down a barrel with the optimum twist for its caliber, form and mv, will be more accurate than if it were fired down a barrel with an other than optimum twist. While it is possible to over-stabilize a bullet, accuracy suffers first when a bullet is under-stabilized, by being fired through a too slow twist. (It fails to develop enough gyroscopic stability to minimize the effects of perturbances in its flight path.) Since, in any given cartridge, safe muzzle velocity decreases as bullet weight increases, a twist siutable for a light or mid-weight bullet will not optimally stabilize a heavy-for-cartidge bullet.
Rifle manufacturers must strike a happy compromise, choosing a twist rate that suits best for the most effective bullet weight range for any particular cartridge.
Only if your shooting is higly specialized - long heavy bullets for long range, for instance, do you really need to concern yourself with any but factory rates of twist.
Rifle manufacturers must strike a happy compromise, choosing a twist rate that suits best for the most effective bullet weight range for any particular cartridge.
Only if your shooting is higly specialized - long heavy bullets for long range, for instance, do you really need to concern yourself with any but factory rates of twist.
Greenhill
