Bullet Weight vs Barrel Twist
When it comes to picking the right twist rate for you barrel, you need to ask yourself what type of ammunition you will be using. For lower grain bullets you are going to want a higher twist rate. Most military rifles like the M4 will come with the twist rate of 1:7 for use with the M855 5.56 round that has a weight of 66 grains. This is ideal for the 1:7 twist.
If you are going to shoot a lower grain bullet, let’s say XM193 round that has a 55 grain bullet, you would be better off using a rifle barrel that has 1:9 twist. This will allow maximum twist to stabilize the bullet in flight without over rotation or under rotation for the lighter bullet.
For those that are unsure, your best choice would be the 1:8 twist rate. This will allow you to get the best performance out of your barrel when shooting different grain bullets. Take a look at the chart below to see what will work best for you.
Of course if you are not too concerned with accuracy or optimizing the best twist rate for your style of shooting, you could just go with straight lands and grooves like the Franklin Armory Reformation with a 4" MOA @ 50 yards......