twist rate - too fast?

[wmitty]

I'm sure some of you have noticed in the Fouling Shot that one shooter is shown to be using a Hart barrel with a 1/14'' twist to stabilize the rcbs .30-180 sp at 2100 fps. (rotational speed of 1800 rev/sec) Would there be any significant accuracy improvement in a hunting rifle using cast by going to such a slow twist rate.? I realize the benchresters are using the slow twists to minimize the effect of imbalance with their bullets and I wondered if someone who has "been there" would express their opinion.

[Larry Gibson]

I'm sure some of you have noticed in the Fouling Shot that one shooter is shown to be using a Hart barrel with a 1/14'' twist to stabilize the rcbs .30-180 sp at 2100 fps. (rotational speed of 1800 rev/sec) Would there be any significant accuracy improvement in a hunting rifle using cast by going to such a slow twist rate.? I realize the benchresters are using the slow twists to minimize the effect of imbalance with their bullets and I wondered if someone who has "been there" would express their opinion.

Yes, to answer the question. It is increasing RPM tyhat invariably causes inaccuracy. With hunting rifles using alloys for the cast bullet of malleable nature instead of those that shatter can maintain accuracy of 2 MOA or less upwards of 130,000 RPM. This is in the 1800 fps range for a 1'10" twist, 2000 fps range for a 1-12" twist and 2500 fps with a 1-14" twist barrel.

If one is willing to accept less accuracy than 2 MOA then the velocities can be pushed a little farther. Just depends on what is "acceptable" accuracy. Also I developed a load using a 311041HP cast of WQ'd shot (3-5% antimony) in my M94 30-30 with a 1-12" barrel. This load pushing right at 2100 fps out of a cold clean barrel will put the first 5 shots into 2 - 2.5" at 100 yards (with aperture sights). Shoot 5 more shots from the now fouled barrel and the group is around 5 MOA. Clean the barrel (no real leading so normal cleaning routine is fine) and the next 5 shots go back into 2 - 2.5". Point here is that is a great hunting load as I've yet to shoot more than 2 shots when hunting so the accuracy limitation of the first 5 shots is moot. I've a load identical to this performance in a .308 Win M70 with a 1-12" twist.

That being said I have shot some 3" groups at 2500 - 2600 fps from a 1-10" twist 30-06 with some hard cast bullets of a special bore ridng design weighing 154 gr. I've been told they work well on deer but I've no first hand knowledge in that regards. As a comparison neither the Lee 312-155 or the RCBS 30-150-FN when cast of linotype will hold that accuracy level at that velocity.

Larry Gibson

[felix]

One reason lead boolits take less twist is because lead is replacing the copper on the outside diameter. The heaver the boolit is for a given length, the less twist is required for the same stability. Because jacket material is roughly the same thickness for all condoms (jacketed bullets), the smaller the boolit caliber, the better the advantage gained using lead boolits with factory" twists. ... felix

[Bass Ackward]

I'm sure some of you have noticed in the Fouling Shot that one shooter is shown to be using a Hart barrel with a 1/14'' twist to stabilize the rcbs .30-180 sp at 2100 fps. (rotational speed of 1800 rev/sec) Would there be any significant accuracy improvement in a hunting rifle using cast by going to such a slow twist rate.? I realize the benchresters are using the slow twists to minimize the effect of imbalance with their bullets and I wondered if someone who has "been there" would express their opinion.


Mr mitty,

Now you have the reason for the superiority of the 35 bore for using cast bullets with bottle neck cases. Best twist rates for cast per bullet weight going.

[wmitty]

Bass, I understand what you are saying about the .35s but I still have trouble removing the thought from my mind that boolets with a higher sectional density (relatively speaking) are what's needed for hunting. I guess this is best described as the "Elmer Keith" syndrome although I think I was infected by Bob Hagel's book "Game Loads and Practical Ballistics for the American Hunter". I have paid close attention to what you have written concerning higher sectional density cast boolets and alloy strength. So failure is due to a lack of compressive strength and even a relatively low muzzle pressure can't overcome the problem of a distorted boolet?


Thanks for all your replys to the initial question!

[Char-Gar]

I had for a number of years a Springfield 03, 3006 with a Phfier 1-14 twist barrel. It would shoot condom bullets up to 165 grains very well, but the 180s went wobbly. It would shoot 180 grains cast like a champ.

It is the length of the bullet that matters and lead bullets are heavier for their length than condom bullets.

I never tried that rifle with cast bullets heavier than 180, so know knowledge on how heavy you can to with a 1-14 twist 30 cal barrel.

[Bass Ackward]

Bass, I understand what you are saying about the .35s but I still have trouble removing the thought from my mind that boolets with a higher sectional density (relatively speaking) are what's needed for hunting.


Mr mitty,

I have killed numerous game with almost every bore diameter going. The 35 is the most consistent killing machine for deer that I have ever had my hands on. And the beauty of it is you couldn't tell if you were shooting cast or jacketed judging from the game's reaction.

No other bore diameter has shown me that before.

[wmitty]

I think it finally has dawned on me what you are saying, Chargar. The lead alloy boolet is more dense than the jacketed bullet of the same weight and is therefore shorter, allowing stabilization at a slower twist rate. Now I see!

Thanks, fellers!