Bullet length is more critical than weight for stabilization. From left to right: 67-grain Hammer 80-grain Barnes TTSX 100-grain Hornady InterLock 100-grain Swift Scirocco and 90-grain Hornady GMX. 25 caliber cartridges, stabilizing almost all. 250 Savage load, Arthur Savage changed to 1:10, still the standard twist for most. In 1920, with the introduction of a 100-grain. In 6mm, the difference between 1:10 and 1:12 proved a deal-breaker. 223/5.56 NATO-the smaller the bore diameter the more critical correct twist becomes, especially as projectiles continue to develop. 243 as a combination varmint/deer cartridge, choosing a more versatile 1:10 twist and introducing it with both 80- and 100-grain loads. 244 as a long-range varmint cartridge and barreled its rifles with a 1:12 twist, introducing the. The best-known exception is the situation between the. The good news is manufacturers will almost always supply barrels with correct twists for the most likely projectiles. Twists that are too fast seem more likely to simply yield poor groups. In my experience, keyholing is more common with twists that are too slow to stabilize the bullet. Clockwise from top left: 62, 69, 70 and 73 grains.
Accuracy suffers with heavier bullets, but in this barrel tumbling is unusual. Then bullets may tumble end over end after exiting the barrel. If the rate is too slow for the projectile, accuracy will typically deteriorate gradually until a breaking point is reached. Generally, there is a range of suitable projectiles, not an abrupt precipice like I encountered with that. 45-70 is standard with a 1:20 twist because the most common projectiles are relatively short and light for caliber. Slow twists are uncommon today, but they still exist. 30 caliber cartridges designed for longer bullets have a 1:10 twist. Roundnose bullets are shorter for weight than sharp-pointed, spitzer bullets.
Of these, projectile length, or at least the bearing surface that contacts the rifling, is critical. The formula for determining a proper stabilizing twist considers the length, weight, and shape of a projectile. Rifling twist imparts gyroscopic stability to a projectile, enabling much greater accuracy than a smooth bore. Yep, it’s light for caliber, but it stabilized, and I’m able to push it to almost 3,200 fps with no pressure signs. My friend Kyler Hamman directed me to Hammer Bullets in Idaho, which makes a 67-grain 0.257-inch copper bullet intended for the old 1:14 twist. 250 Savage rifles were barreled with a slow 1:14 twist for the initial 87-grain load.
I should have known that before 1920 all. I have dies, so I loaded a few 90-grain GMX, but if the bullets hit paper at all, they hit sideways. Thing is, I wanted to use it on the Central Coast, but there are no California-legal unleaded factory loads in. Between my eyesight and the irons, I’ll never know how well it really shoots, but it grouped just fine with 100-grain Hornady InterLocks. 250 Savage from my buddy Joe Bishop’s widow-clean, in great shape, flip-up aperture. Yeah, I know I’m supposed to know everything about sporting rifles.
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