Location: The rifle range, or archery range or behind the computer in Alaska
Re: Barrel Twist
You were getting your idea of below 2800 FPS by the green hill formula. His formulas dictate differant twist needs for differant velocity. 1500-2799 uses 1 constant and 2800 and above uses nother constant in the formulas. The faster you drive a bullet the less twist is needed. Most modern calcs use a gradual increase or decrease instead of 1 FPS being the deciding factor.
The JBM website has a very usefull twist calculator as well as the RSI and Reloaders Archive computer programs.
I hope that helps your research.
Long range shooting is a process that ends with a result. Once you start to focus on the result (how bad your last shot was, how big the group is going to be, what your buck will score, what your match score is, what place you are in...) then you loose the capacity to focus on the process.
Maybe a short description of a lengthy subject may help. You have two factors working against each other when considering barrel twist rates. First is the bullet's imbalance. Most bullets center of gravity and center of spin are not going to be perfect, considering manufacturing tolerences and what happens to a bullet from the forces during firing. The faster you spin a bullet the more it will wobble due to this imbalance, , the worse the dispersion will be, and the bigger your groups will be. For this reason, you would want the slowest twist possible to stabilise you bullet and and keep this effect to a minimum. The second factor to consider is from the bullet's impact with the atmosphere. I believe this has a greater effect on a bullet's stability than the first. This impact with the atmosphere causes the bullet to yaw. To overcome this, you have to spin the bullet faster. As you can see, you have to compromise imbalance stability for atmospheric pressure stability. Will you be using the gun for target shooting or hunting? Will you always hunt in the same area or maybe an elk hunt in the mountains and a deer hunt at sea level? If your going to use the gun at varried locations, you should probably go with the faster twist rate. Here is a link with some outstanding information on the subject:
Elroy, thanks I know understand the topic a little better [img]/ubbthreads/images/graemlins/smile.gif[/img] I will be using the rifle as a long range piece and hunting rifle in varied locations etc as you suggested so I guess a faster twist would be better?
Thanks again all
Vegitarian is an old indian word for lousy hunter