Barrel Twist Rate
Would appreciate information on how the twist rates are determined for barrels.
Also, are the lands and groves different sizes and depths for different calibers??
Many thanks, 11thcanopy
Also, are the lands and groves different sizes and depths for different calibers??
Many thanks, 11thcanopy
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A twist rate of 1:10 means the bullet makes one complete turn (twist) for every 10 inches of barrel length. In a 20 inch barrel the bullet would turn completely twice before it exits. The faster the rate, the more a bullet spins after it exits the barrel. Most centerfires use a relatively fast rate of 1:9 or 1:10. The longer the bullet, the faster the twist rate you need to stabilize the bullet in flight. If the twist rate is too slow, the bullet may tumble. Muzzleloaders that shoot round balls (very short length obviously) need only a 1:66 spin or twist rate, but load a long heavy bullet in the same type gun, and you need a faster rate, say 1:24 or 1:48. The best rate can be determined by formula or experimentation 0 -
There is no industry standard on size and depth for lands and grooves. Marlin uses a "microgroove" rifling technique on most of its rifles. The grooves are very shallow, but there are many of them. This works well for jacketed bullets but not as good for cast lead bullets. Marlin uses a "ballard type" rifling (deeper and fewer grooves) for guns that may be used for heavy cast bullets (.45-70 for example. Deeper grooves take a deeper "bite" and give more consistant twist and stability. The military often used this type rifling as well. Many rifles have 4 sets of grooves, but some, for example, the 1903-A3 Springfield used only 2 to cut costs and speed production. Most rifling twist rates are constant from one end of the barrel to the other but Italy used a progressive rate on some of its military rifles. It started very slow, then the rate got much faster near the muzzle. These Carcano rifles are the only ones I know of that used this system, though there may be others. The rifling systems used to stabilize bullets vary greatly through time and regions. A book could easily be written on this topic. 0 -
Twist rates are determined by the Greenhill formula. This formula takes into account the length, weight and diameter of the bullet. 0 -
Here is some good info on the importance of twist.
http://www.lostriverballistic.com/LRB/DocsCorner-Twist.cfm
Mad Dog0 -
Checking the twist rate of a barrel is as simple as running a cleaning rod with a tight fitting patch down the barrel and measuring the amount of inches it takes to go one complete revolution of the rod......
I hope this helps a little......
mrbruce
Gun control is hitting what your aiming at.0 -
the greenhill formula was developed for artillery shells (1lb) and is only an approximation. Do some searches and you will find refined versions of that formula for rifle projectiles.
Simple explanation:
the faster the twist, the heavier and longer pills it will stabilize,..AS WELL AS the shorter, lighter ones. The slower the twist,..the more limited you are in the weights of bullets you can stabilize. However,..in an extremely fast caliber (220swift for example) the RPM's generated by 4100fps and a 1:7 twist tube will tear the jackets off of light bullets with varmint jackets and they will explode in flight, even the VLD 80gr pills in some barrels. In that case,..the twist has to be slowed to reduce the RPM's.
Go to Shilen's website,..they have a chart for all calibers and twist rates for all available bullet weights.
why chase the game when the bullet can get em from here?....
Got Balistics?0 -
Thanks to all for the information.
The reason for the question is that we really want to build a rifle for the 10 mm cartridge to go along with our pistol.
So we are just in the thinking stage for things like rate of twist given the available bullets for the round.
We have saved the sites mentioned.
Thanks again.0
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