First outing with the #301618 NOE boolits

[Doc Highwall]

It is bullet caliber and length, twist, and velocity. The weight of the bullet is not a factor only length is.

[wmitty]

Yes, I should have asked what length of boolit Nobade thought the 15" twist rate would stabilize. I jumped in with out engaging the three brain cells I have left. I was wondering if the rest of those interested in paper patching for a hunting boolit load in thirty caliber would consider it worthwhile to go with a slower twist rate barrel (say 1:14") rather than the 1:10" we are normally working with. I have two of these in .300 Win Mag that I picked up for the 700 Rem action that I currently have a .375 H&H barrel mounted on. I think I have seen comments by Nobade and someone else here commenting about going with a slower twist .30 caliber barrel with paper patched slugs; to me it seems the way to go if hunting with a relatively high sectional density boolit is capable of being stabilized. Guess I am just trying to justify the cost of a slow twist rate barrel.

[Nobade]

According to Greenhill, a 1:14 will work with a boolit 1.016" long and a 1:15 will work with one .948" long. However, that is a bit conservative and especially here at 5300 ft. I can get away with a little more boolit than I could at sea level.

As for the 1:10 vs 1:14 in a 300 win mag, the 1:14 will give you a easier time finding accuracy with high velocity cast boolits, if they are patched or not - at least in my own experience. I know lots of folks poo poo that idea, but I have consistently seen it to be the case in my own experimenting. As they say, YMMV!

-Nobade

[Doc Highwall]

The original tests shot by the NRA with paper patched bullets that led to Lyman making the two paper patch moulds was shot using a 300 Winchester Mag at I believe 3000 fps. What is the standard twist for the 300 Winchester Mag 1-10"?

[Nobade]

Yep. I didn't say it couldn't be done - I just find it's easier with a slower twist.

-Nobade

[Harter66]

I was just running some numbers through the strelok calculator for hold over and drift. With a BC of.286 and a sedate 2300 fps for the 172gr reasonably attainable in an 06 or 308(maybe),it has a 1000 yd hold over of 1048 inches (87 feet 4 inches). It's just 26 feet at 750. How does one go about gauging that with an 03A3 GI peep and blade? I guess I'll have to get my spotter up to speed.

[303Guy]

The weight of the bullet is not a factor only length is.

I don't believe that is correct. The length determines the tipping forces while the gyroscopic force determines the resistance to tipping, i.e. stability. Gyroscopic force is a function of mass and angular speed which is in turn a function of the spin rate and diameter. So I'd suggest that the weight (mass) plays an important role in stability. Correct me if I'm wrong here folks.

[Nobade]

You are correct, but it's a question more of density than weight. A pure lead bullet of the same shape will be a bit more stable than one made of Linotype or copper or whatever. But with the materials we use for bullets it's not a huge range to choose from.

-Nobade

[Harter66]

There are gobs of physics involved also. I have a 308 that for whatever reason just refuses to shoot anything over 170 gr. The 180 RN I tried in it was actually shorter than the 150s and 168s. With that said generally we can shoot a heavier cast than jacketed because the cast is shorter per weight. The 308 above tumbles a Barns X 165 simply because it is too long . I suspect that it would do the same with many of the other high BC bullets. Shape enters into the physics of the bullets flight as well , it involves centers of gravity,lift and about 3 other force points . I understand it and could discribe it but to talk about in correct terms escapes me. The latter parts explain why a boat tail and rebated base are more effective at sub and transonic speeds than at super sonic speeds and why some shapes with only a tiny change in ogive length will fly stable but tumble on impact. I hate the football description of balistic stability but it's the easiest 1 to see. In the case of 30 cal we can use a 1-14 twist for a 150 gr 2700 fps spire point cup and core bullet, a pure copper bullet of like shape and weight may or may not stabilize and a 170 fp cast lead will stabilize. Sometimes a semi wad cutter that is completely outside of the "normal" window will also ,but because of aerodynamic effects on the shoulder rather than spin and length. Velocity enters into it also and while mechanically I don't get it mathematically it works out and delivers on target. It explains why a bullet can be shot in the same slow twist and shoot well from a 300 WM that won't from a 308.