07/01/2018
FYI... AR 15'S TWIST RATE'S EXPLAINED.
Common AR-15 rates of twist vary between 1:7 and 1:12, but why should you care what your rate of twist is, right? The reason is because different bullet weights perform better with certain rates of twist. So if you are just going to go plinking and do short- to medium-range target shooting, you may be happy with 40 grain bullet weights, which would mean a 1:12 rate of twist would be ideal for you.
If you are shooting long range, or want more pe*******on, you want a heavier bullet in the AR, such as a 62- or preferably a 77-grain. 62-grain bullets prefer a rate of twist around 1:8 and 77-grain bullets weights favor a 1:7 twist rate.
All of this being said, these days finding ANY AR-15 ammo is almost like winning the lottery, and if you are lucky enough to find any at all it is likely going to be the most common bullet weight which is 55-grain (a 1:9 twist rate). Ideal rates of twist for a particular bullet weight are somewhat subjective; however opinions will not vary greatly among the experts.
Bullet Weight: The Ideal Rate of Twist
So to simplify this for you, here is a chart you may want to print:
Bullet Weight Twist
40-Grain 1:12
55-Grain 1:9
62-Grain 1:8 or 1:7
77-Grain 1:7 or 1:8
80-Grain 1:7
As you can see from the chart, the heavier the bullet you want to shoot, the faster the rate of twist should be to most effectively stabilize the bullet. It’s not that you can’t shoot AR ammo that is on one end of the spectrum through a barrel with a twist rate at the other end of the spectrum, it’s just not ideal. You won’t get maximum effectiveness of your ammunition. One thing that can happen is over-stabilization; this occurs when you shoot a bullet through a barrel with too fast of a rate of twist for that particular bullet weight.
Here’s an example: you shoot a 40-grain AR bullet through a barrel with a 1:7 rate of twist; the bullet will over-stabilize and this will make the bullet not fly completely true at longer ranges. But you wouldn’t want to shoot a light AR bullet at long ranges anyway.
reposted from the shooters log....