Here is a calculator for the velocity adjusted Greenhill formula that allows you to change the inputs and see the results. Change the entries in BOLD RED to see results. It is also conditionally formatted so you can see what bullet length and velocity work the best for your known barrel twist +/-1".

Also worked for me - Win XP/Firefox/Open Office.

Thanks for sharing !

Phil

LRF ... both tables download - open - saved to computer directory and work
Noticed changing the 150 multiplier to 125 in the twist rate table did not change any output values

LRF - I downloaded the zip table that bohemianway posted.
* Opened the zip fie
* changed the multiplier between 125 & 150 for 0.308
No values changed in the table

Question:  how do I change the table output to a graph format?

Sorry for the confusion. On mine the only cell you change is the "Diameter" of the bullet. Remember it is a velocity table therefore the 150 and 125 are simplification constants are built into the formula.

Some things to remember regarding stability besides what have been talked about are:

1. Sectional density (SD)

2. Position of the center of gravity. Basically that will change with nose shape.

3. Effects of transonic on bullet stability.

Also, if you'll remember, the Army did some accuracy testing with the 45/70 at 1/4 mile or futher with a 22 twist and the 500 gr bullet, I don't remember any descusion of lack of stability in those trials.

I'm not a LR shooter so, I'm out of my league regarding personal testing that I've done but, for 200 yards or less with Simi-spitzer or spitzer nose shapes, the basic Greenhill formula can use the constant of 175 in our basic 14 - 1500 fps range but, as noted above, there are other factors that will need to be considered.

The first thing that I discovered happened in 1986. I got a close friend into the sport and when I bought my rifle, I thought I had a standard 16 twist and I bought what was the current Ron Long mold for it (1.16" lg). My friend had a HW and I told him to get a Douglas 16 twist barrel and that RL bullet well, it just wouldn't shoot (of course) and tipped all over the place. I then checked my twist, because mine always shot well and discovered that I had a 15 twist barrel. I felt bad that I hadtold him what to get so, I cut .050 off of his base band and from that moment on, his rifle shot just as well as mine!!!

I then played with the GH formula and found what I had to do was change the 150 constant to 175 and mirrored the change that I had done with his twist and bullet lenght. I then used that factor untill I discovered JMB program. 

From there, I found the Geoffrey-Kolbe program about 3 years ago and that program has the best results for at least 200 yard cast and any range jacketed bullets.

For ~200 yard shooting faster twists give NO benefit and can give less accuracy at that range. I say this because I don't want people interested in Schuetzen to think they should get a fast twist barrel.

Frank

Quote:

Frank, that would be the 2 Mile Shoot at Sandy Hook (NJ) with an 1873 Trapdoor 1:22 twist
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