.270 twist rates and 150gr. bullets

2000Z-71 · Apr 23, 2009

When I bought a box of Barnes TSX 150 grain bullets for reloading my .270 I noticed the sticker on the box that recommends a 1:9.5 twist or faster. I didn't think anything about it and bought them anyway. I get homw and pull up the specs on my Winchester 70 and it has a 1:10 twist rate.

I'm not overly concerned but just wondering about the rationale of it. Also wondering it this is typical for the heavier bullets in .270. I've only shot and reloaded 150gr. loads in this rifle and I've gotten groups less than 1". Just curious more than anything else.

2000Z-71 · Apr 23, 2009

When I bought a box of Barnes TSX 150 grain bullets for reloading my .270 I noticed the sticker on the box that recommends a 1:9.5 twist or faster. I didn't think anything about it and bought them anyway. I get homw and pull up the specs on my Winchester 70 and it has a 1:10 twist rate.

I'm not overly concerned but just wondering about the rationale of it. Also wondering it this is typical for the heavier bullets in .270. I've only shot and reloaded 150gr. loads in this rifle and I've gotten groups less than 1". Just curious more than anything else.

OKFC05 · Apr 24, 2009

Short answer is that it is close enough for jazz, so shoot away. It helps to stick to higher velocity with the 150gr.

Long answer is that the longer the bullet, the more RPM it must turn to maintain a stable nose-forward attitude during flight. You get this with higher velocity and faster barrel twist. This is especially noticeable with ultra-long brass bullets. The .270 with 1 in 10 twist is optimum for about 130 to 140gr lead core bullets.

Each projectile will precess (move the nose in a slight circle) or wobble as it moves downrange. The more symetric the bullet and the greater the stability, the smaller the circle.

As the bullet slows down, it will reach a point where it actually turns from Beta (conditional) stability with the nose forward, and moves into the Alpha stability with the rear (heavy) part of the bullet leading.

All rifle bullets at maximum range tend to land rear foremost, as has been seen in many wars. So if you could somehow recover your .270 bullet at 1 1/2 miles, it would be traveling backwards.

.270 twist rates and 150gr. bullets

2000Z-71

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