Twist of Rate?
Can someone tell me more about Twist of Rate as to how it affects what bullet you need,size powder charge etc. or where I can find some info, in ENGLISH.
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If you mean 'rate of twist' it is the number of inches it takes for the bullet to turn around once in a gun barrel. Such as a 1 in 10 twist, means the bullet turns once in 10 inches. For any of the other information, it can be found in the info section of any good reloading manual or try Cartridges of the World for all you ever want to know!Good luck !
dan0 -
Also, your rate of twist will be what is knows as either "heavy" or "light" for whatever caliber you are using. Now, most factory guns, from whatever manufacturer, will be close to the same as all others. They are made to be a mid range barrel as far as twist rates go, this way they will shoot most all weights of factory ammo, MODERATELY well.
General rule is :
Heavy twist groups heavy bullets better
Light twist groups lighter bullets better.
here is an example, colts as well as all other AR15 varaints come in several twist rates, which are 1:7, 1:9, and 1:12. The 1:7 is the heavy twist barrel, because it will twist the bullet one revolution in only seven inches of barrel where the lighter twist barrel (1:12) will only twist the bullet 1 revolution in 12 inches of barrel. My experience is that the heavier bullets, of a given caliber, need to be twisted in a greater revolution, to stabilize properly, and the lighter bullets stabilize with less revoultions. That is why Nat'l match AR15/M16 barrels are stamped 1:7. They are able to stabilize the longer and heavier 69 and 75gr bullets, which as a result of their longer design and heavier weight have a higher Balistic coefficient. the balistic coeficient of any given bullet is a function of its weight, length, and surface area. This all translates into a heavier and therefore, longer bullet, being able to overcome wind drift and gravity for longer distances. Physics laws state that an object of greater mass, will retain it's energy over greater distances than will a smaller mass object, propelled at the same velocity. That being said, heavy twist rates are for heavier longer range loads, and lighter twist rates are for lighter, shorter range bullets.
You will hear folks say that they can get this and that, and the other, weight of bullet to group the same in their rifle. That may be true, but all they have done is adjusted the powder charge to propell the different weighted projectiles at the speed necessary for that weighted projectile to be stabilized by that twist rate. Quite often, it is dropping powder charge, which decreases velocity, and therefore, you have effectively reduced your impact energy. IMHO all this can be acheived much easier by just buying a smaller caliber and shooting the bullet which it likes best, and not spending all that time on the loading bench. I like my twist rates to stabilize the bullet I want to use, and do so at near max. pressures. that's the point of the caliber, not to be downloaded to produce the enrgy of a smaller caliber just for the sake of grouping a bullet the barrel didn't like in the first place. That is the whole reason twist rates exist, so you can choose a rate of twist which is conducive to sub MOA groups in the weight range of bullet you wish to use. If that wasn't the science behind it, all like calibers by all manufactureres would have the same twist rates.
Are you thoroughly confused yet?
I'm a man,....but I can change,.....If I have to,......I guess.0 -
Just a noteon this. It's asier to call it "fast twist" or "slow twist" less confusing! A fast twist 17 calibr barrel is 1 in 6" and will stabilize the 35 grain VLD(very low drag) bullets but will vaporize the little 20-25 grain bullets in a very short distance! Whn Remington came out with the 244Remington they used a 1 in 12" twist in the barrel. They were phenomenal with bullets of 85 grains or less but were "too slow twist" to stabilize 100 grain bullets that would have made the 244 a very useful gun for varmints to deer. Winchester brought out the 243 using 1 in 9.5 inch twist and took the market by storm because they had a caliber that would handle light varmint bullets and the 100 grain deer bullets. Remington then reintroduced their same case and called it the 6mmRemington but had a twist of 1-9 or 1-10 and they had a winner! But the 243 had already gained market share and still has it today. GHD 0 -
JustC, that was a great post. Everything is correct, and well said. D@D, the caliber was not mentioned in your original post. I'm sure this will have a impact on what twist rate you will need.
Rameleni10 -
I have a couple Remington model 700 in both 270 and 308cal. Thanks for the posts as always very informative. 0 -
D@D....here's more on the subject:
http://www.loadammo.com/Topics/July01.htm
http://www.schuetzen.net/rifling_twist_rate.htm
http://www.snipercountry.com/hottips/TwistRate.htm
"Teacher, may I leave the room. My brain is full.)0 -
There's something called the "Greenhill Formula for Twist":
Twist = (150 x bullet diameter)/(bullet length to diameter ratio)
The book says this formula works for "jacketed, sharp point bullets" as well as (I assume) round-nosed jobbers. The book also says this formula works well for velocities up to 1800 fps, and for faster bullets, use 180 instead of 150.
Example: A .308 caliber bullet 1.125 inches long
Twist = (150 x .308")/(1.125"/.308") = (46.2")/(3.653) = 12.65"
which means the Twist should be 1 turn in 12.65 inches.
I think, though, that there is a more detailed and sophisticated form of the Greenhill Twist Formula out there....0 -
To make it simple go to "SST's Rifleroom". There is twist rate info from Shilen that covers calibers and bullet wgt./
Bud0 -
Go where Bud? 0 -
To determine rate of twist for your rifle, simply insert a cleaning rod with a tight patch into the breech. Mark the depth of the rod with a peice of tape and push in until the rod has made one rotation. Mark again and withdraw the rod an measure distance between tape edges to determine twist rate. 0
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