More than the barrel length itself, the twist rate matters a lot with the Blackout 300 upper. You’ll probably hear different misleading theories and mostly wrong opinions, but it’s all rather simple if you do the math.
So, between 300 Blackout 1-7 vs 1-8, what’s the ideal twist rate? Together with my team of experts, I shot a few rounds out on the range and came up with these results.
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What’s the Difference Between 300 Blackout 1-7 & 1-8?
Most AR-15 upper 300 Blackout rifles feature the 1:7 and 1:8 twist rate, which is the rifle barrel’s spin rate. We refer to it as one rotation over a particular inch of barrel. With a 1-7 twist rate, for instance, it means that the bullet will be spun once over 7 inches of rifling. That’s 8 inches of barrel for the 300 BLK 1-8.
In this ratio, the smaller the second number is, the faster the bullet spins, while a larger second number will indicate a slower rate. If the twist rate isn’t fast enough, the bullet may not travel with stability, leading to inaccuracy downrange.
Ideal for self-defense and match rounds, the Blackout 300 1-7 twist rate is the path most barrel manufacturers are going. The 300 BLK may have started with the 1:8, but most premium barrel users have shifted to the 1-7 as it stabilizes everything it can shoot. For the 300 Blackout suppressed and other suppressors, the 1:7 twist rate benefits heavier subsonic rounds.
When it comes to competition guns and precision firing, the 1-8 rate is popularly regarded as the most universal as it can handle most bullets that run in an AR-15 platform, such as the Blackout 300. The 1:8 twist ideally works with lightweight supersonic rounds.
Ideal Twist Rate Based on Bullet Weight
- 1:8 or 1:7
- 1:7 or 1:8
Based on the chart, if you plan to use a heavier bullet, choose a faster twist rate to ensure stability. Generally, you can still shoot through 300 Blackout barrels with a twist rate that’s at the end of another fence, but it won’t ideally give you the maximum ammunition performance.
Key Factors to Consider
Twist Rate Over-stabilization
When choosing between 300 Blackout 1-8 or 1-7 twist rates, consider over-stabilization. This usually happens when you shoot a bullet through a gun barrel with a faster twist rate than what’s required for the particular bullet weight.
For instance, if you shoot a 40-grain bullet through a BLK 300 with a 1:7 twist rate, the bullet tends to get over-stabilized, and this won’t make the bullet fly entirely true at a longer range. 
In determining twist rates, the bullet weight’s role is more of a correlation. A significant factor in choosing the right twist rate boils down to the length of the bullets. The reason weight comes into the picture is because the longer the bullet, the heavier it will be. And the heavier it is, the faster the twister rate you’ll need to reach stability in that round in flight.
For bullets, you might want to take a look at 6.5 Grendel vs 308 here.
1-7 & 1-8 Twist Keyholes
When picking between the 300 Blackout 1-7 vs 1-8 twist, the main goal is to find an AR-15 barrel that will give your rounds the straightest and flattest trajectory by spinning it at just the right amount.
When an AR round isn’t stabilized, the bullet tends to topple end-over-end and will hit the target on what is usually known as a “keyhole” shot. A keyhole shot is characterized to take the shape of the actual bullet when creating a bullet hole.
If the twist rate is extreme, it tends to put too much spin, and over-spinning will cause keyholing. This can be dangerous as excessive spins may cause a round to fragment and send lead or other debris flying off.
When it comes to twist rate accuracy, there is no “one size fits all” concept. There is no all-inclusive twist that will work for any of your cartridges or any single cartridge in the market, for that matter. To be accurate, twist rates need to match the components of the bullet you’re firing. If the rate is too low, there won’t be enough round spin. This will lead to destabilization in the air.
To give you a clearer picture when choosing between the BLK 300 1-7 and 1-8 twist, let’s look at the same physics as throwing a football. When you throw a football, you impart spin to stabilize the ball to help it reach precisely where you aim. The same thing happens when you impart spin on a bullet using the barrel rifling.
Twist Rate Over-spinning
One of the more common concepts you may have heard about twist rates is that a heavier bullet requires a faster twist. While this isn’t relatively false, it’s not entirely true, either.
As per our experience, the longer (not heavier) bullet needs a faster twist. Choosing otherwise may result in over-spinning. Generally, longer bullets are heavier, but there are exceptions when it comes to specialty rounds.
If we dig into its scientific application and dynamics, a long object moving through air is naturally more unstable and will require more stabilization. With inadequate spin, the rounds will topple over, eventually destroying your range and accuracy. But, it is just as important to make sure that you do not over-spin a bullet as over-spinning may also result in inaccuracy and possible ripped rounds.
We like shooting long-range, so either the 300 BLK 1:7 or 1:8 twist rate works fine. However, one drawback to this is that when you have a faster twist rate, the barrel will also wear out faster.
On the basis thereof, know your purpose or intention first. What kind of shooting do you envision doing? Once you’ve determined that, it will be easier to pick between the 1-8 and 1-7 twist rates.
Looking for long-range bullets? 5.56 NATO and 6.5 Grendel are good options.
300 Blackout 1-7 & 1-8: Final Verdict
When choosing between the 300 Blackout upper 1-8 or 1-7 twist rates, keep in mind that this barrel isn’t initially designed for hunting. The BLK 300 is fashioned as a subsonic cartridge to complement and enhance the suppressor technology. ACC, the company that developed the Blackout 300 cartridge, recommends the 1:7 twist rate. But, if you won’t be using it for subsonic loads, you may find the 1:8 rate as a better choice.
- Over-stabilization and over-spinning affects accuracy
- A heavier bullet requires a faster twist rate
- 1:7 twist rate is designed for heavy, subsonic rounds
- 1:8 twist rate performs best in lightweight supersonic rounds
Need a rifle? We highly recommend TC Compass and Ruger American.