Rifles - Cartridges - Ballistics - Copyright.
Rifling Twist Rates
Rifling Twist Effects
Rifle Barrel Break-In
Rifle Barrel Cryogenics
Rifle Barrel Free-Bore
Rifling Twist Effects:
 Not all bullets are of the same hardness therefore will also expand differently according to rifle barrel length and rifling twist rate. Either too much expansion of the bullet or not enough, of which, results in very poor performance for hunting use.

Bullet Centrifugal Force:
 The centrifugal force of a bullet helps to expand the bullet when the bullet impacts a solid object. Velocity and rifling twist rate determine the ballistic centrifugal force of a bullet so barrel length and barrel twist rate together changes the bullets centrifugal force and as a bullet travels downrange the R.P.S. value is constantly decreasing.
R.P.S. = Revolutions Per Second = Centrifugal Force Value.
Note: Higher R.P.S. = More Expansion Of The Bullet.
Ammuntion: Winchester, .243 Winchester.
Bullet Diameter: .243 Inch.
Bullet Weight: 100 Grains.
Bullet Ballistic Coeffecient: .356.
/ FPS. = Feet Per Second.
/ FT.LBS. = Foot Pounds.
/ IN. = Inches.
/ RPS. = Revolutions Per Second.
Rifle Barrel Length: 26 IN.
Bullet Muzzle 200 Yds. 400 Yds.
Velocity / FPS. 3,010 2,495 2,035
Energy / FT.LBS. 2,012 1,382 920
Trajectory / IN. - 1.5 0 - 21.2
1 in 9" Twist / RPS. 4,013 3,326 2,713
1 in 10" Twist / RPS. 3,612 2,994 2,442
1 in 12" Twist / RPS. 3,010 2,495 2,035
Rifle Barrel Length: 20 IN.
Bullet Muzzle 200 Yds. 400 Yds.
Velocity / FPS. 2,860 2,361 1,916
Energy / FT.LBS. 1,816 1,238 815
Trajectory / IN. - 1.5 0 - 23.9
1 in 9" Twist / RPS. 3,813 3,148 2,554
1 in 10" Twist / RPS. 3,432 2,833 2,299
1 in 12" Twist / RPS. 2,860 2,361 1,916

Bullet Failure, Over-Expanding:
 A bullet when it first exits the rifle barrel is very hot, almost molten, as it travels down-range it slowly cools and its expansion properties change as well. Bullet heat increases with faster twist barrels as well, friction between bullet and rifling are greater. Longer barrels also increase bullet heat due to longer friction time frame applied to the bullet. Targets engaged at very close distance will most likely result in bullet failure for light-weight bullets giving very little penetration.

 When choosing a rifle cartridge you should always evaluate what you are going to use the rifle for and then select the rifle with the correct rifling twist rate for your imparticular use by bullet weight to gain the most accuracy and correct bullet expansion.

 A good rule of thumb is that the heavier and longer a bullet is, the faster the rifling twist rate needs to be to stabilize it in flight, therefore a lighter shorter bullet needs a slower rifling twist rate to give proper bullet spin for correct flight and expansion.

 High velocity, fast spinning light-weight bullets can disentegrate in flight when fired from fast twist barrels and if they don't blow up before reaching a target, they most likely will not be very accurate and if they do reach the target, penetration value will be very low.

Bullet Failure, Non-Expanding:
 On the other side of this is the very common non-expansion of hunting bullets on game animals, this is normally due to short rifle barrels that feature a slow twist rate and the user tries out the latest heavy hitter deer smashing ammo that features the use of a heavy-weight brush-busting bullet. Out to 25 yards this ammo will most likely work quite well because of the heat the bullet was subjected to prior exiting the rifle barrel, however, at 150 yards all targets engaged simply run off as if nothing happened, problem, non-expansion of the hunting bullet.

243 Winchester Problem:
 For years, this and just this reason alone, higher velocity 80 - 90 grain bullets worked well in 1 in 10 inch twist barrels for deer hunting with a 243 Winchester and 100 grain bullets worked very well with in 1 in 9 inch twist barrels for deer hunting with rifles sporting short 20" - 22" barrels.

Resources And References:
Rifle Scopes
Rifle Scope Mounts
Rifle Scope Mounting
Rifle Sight-In
Rifle Sight-In For Hunting
Muzzle-Loading Rifle Ballistics
Centerfire Rifle Ballistics
Rimfire Rifle Ballistics