The are many benefits to understanding and matching the twist rate of your barrel with the projectile weight you are using. Primarily, accuracy.Ensuring that the projectile coming out of the end of the barrel is correctly stabilised thanks to gyroscopic stabilisation (a spinning object with tend to self-stabilise). Mismatch the twist rates and bullet weight and you can under stabilise – the bullet won’t be flying as true as it could.Too fast a twist rate and the projectile can potentially1 damage the projectile jacket as the excessive force separates the jacket from the core.
Twist rates and bullet weight are often understood, but there are some simple and practical guidelines.But first, a little background.
Twist RateYou can read an expanded article on twist rate over here – but in summary, a twist rate is the number of times your rifling (the groove in your firearm barrel) makes a full revolution over a set distance – this is generally expressed in inches – so a “1 in 10” makes one revolution of rifling every ten inches of barrel length.
Bullet WeightBullet weight has increased as we are reached out further and further with our rifles.A heavier projectile (more grains) will often come with a better (higher BC) – that is, the ability of the projectile to buck wind – they fly truer, for longer.However, it’s not just as simple as putting the heaviest bullet you can down the barrel. More weight requires more powder to move – and speed is still a priority as a slow-moving bullet spends more time in the air, has more time to be affected by the wind, and in the understanding that everything drops at the same speed (thanks, gravity!) the faster it moves, the further it can reach with less ballistic drop.
Matching Twist Rates and Bullet WeightSo, in very simple terms, the heavier the projectile, the faster (lower number) twist rate you are likely to want to utilise.I know, I know, just tell us already – what do I put in my rifle?Well – here is a very basic chart that will set you off on the right foot. Like all things reloading, there are always exceptions.
|Twist Rate||Projectile Weight|
|.224 / 5.56 (your .223 Ar)|
|1:16||Up to 55 grains, 4300 fps or more|
|1:15||Up to 55 grains, 4100 to 4300 fps|
|1:14||Up to 55 grains, less than 4100 fps|
|1:8||70 grains or more|
|1:9||Up to 130 grains|
|1:8||130 grains or more|
|1:15||up to 150 grains|
|1:14||150 to 168 grains|
|1:12||168 to 170 grains|
|1:10||170 to 220 grains|
|1:8||220 grains or more|
This is obviously just a quick list to give you an idea.
Learn More!Keen to learn how to calculate your own twist rate stability factory? Cool. Just click on the video below and for less than the price of shouting me a beer – you can get an extra tutorial on calculating it yourself, using free resources online! I use Vimeo for hosting, but it’s easy enough to join – do it once, and it’s done for good! Thanks for the support!It’s only $3 to rent the video for 48 hours, or, if you prefer, $15 to subscribe to all the videos. Watch them as much as you want!If you want to subscribe, make sure you select that before entering in payment details. If you want, pop over here to see what else we have for you – video.thebloke.co.nz
actually unlikely these days, but there have been reports ↩