Matching, bullets to rate of twist

[Wayne S]

Which is more accurate ?
http://www.uslink.net/~tom1/twistrate.htm

OR

http://www.jbmballistics.com/cgi-bin/jbmstab-5.0.cgi

Example ,one says the 312-155 Lee at .973" long shot in a .308 bore is stable at 1200 FPS the other says 1650 + FPS is required ??

Ain't it always something

[felix]

It's a function of how much stability is required. The typical factor chosen is 1.5, but that is for condoms. Cast projectiles need only 1.3 or less, which means according to your results would be more like 1200 fps. ... felix

[303Guy]

I've had trouble with those calculations because they do not allow for the shape of a cast boolit. A boolit with a boat tail and a long spitzer point has a very different stability to a blunt round nose flat base cast. Specially at the sound barrier zone. Noe do they allow for the weight distribution of a boolit with a blunt and large hollow nose. Nor do they take into account the muzzle blast destabilizing effect.

[44man]

Twist is so much more important then anything else. Guys shooting revolvers ignore it too much but rifle shooters do a lot of work to find what works.
There is NOTHING in print that works. Shooting is the only way to find what a gun likes. There will be a velocity range for about any boolit but now and then one will just not shoot no matter what so it has to be retired from that gun.
Using different twists in a gun also depends on what distances you want to shoot with faster twists needed for long range and slower for shorter distance. An over spun boolit will shoot larger groups at 100 yards then one spun slower but might shoot very tight at 300 or more yards. That is easy to fix by loading lighter for closer ranges but if the twist is too slow and you want to shoot very far, you will not be able to push a boolit fast enough without going over pressure.
My suggestion is to stop reading, none of the charts are correct and Greenhill fails big time. Guys have made it work by juggling figures to match what they shoot, a back door fix so to say that shows the front door is missing.

[1Shirt]

Agree wtith 303Guy. To many variables for accurate comments in my opinion.
1Shirt!:coffee:

[405]

Twist rate tables and calculators are ONLY guidelines, not absolute rules. Bullet shape, how perfect the bullet's form is, the condition and attitude as it leaves the muzzle all figure into the picture. Also, how far the bullet remains stable is yet another variable. All the instability variables are more likely to come into play as the minimums are approached. Additionally, everyone has a slightly different definition for such things as stability and accuracy. Lastly, nothing takes the place of good methods of experimentation, meticulous records and range time.

[canyon-ghost]

Lastly, nothing takes the place of good methods of experimentation, meticulous records and range time.


Exactly, in load development, everyone has to do their own work. That's just how it is.