Best Bullet Weight for 1 in 7 Twist Rate?

By Robert A. Sadowski
Posted in #Gear
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Best Bullet Weight for 1 in 7 Twist Rate?

March 3rd, 2023

6 minute read

Ever wondered how bullet weights and barrel twist rates relate? Robert A. Sadowski examines what is the best bullet weight for a 1 in 7 twist. In the process, he teaches us the basics of everything that’s involved.

As a bullet is fired, the rifling in the barrel forces the bullet to spin. So, in a 1:8” twist, rate the bullet rotates one full turn every eight inches. In a 1:7” twist, the bullet rotates one turn in seven inches. The smaller the number, the faster the twist; you need to remember this.

best bullet weight for 1 in 7 twist
Do you understand the relationship between bullets and barrel twist rates? Can you ID the right .223 bullet weight for a 1:7″ twist? Image: Adobe/Natalia80

There’s a balance between twist rate and bullet weight, sort of a yin and yang of opposite forces that when combined bring balance and harmony. It means all the difference in stabilizing the bullet for better accuracy and terminal performance.

If a bullet spins too slowly, it cannot stabilize and won’t achieve either optimum velocity or accuracy. What occurs is called yaw. The bullet is unstable and does not hit the target with the tip of the bullet, but perhaps the side of the bullet.

1 in 7 twist marking on ar barrel
The SAINT Edge ATC was built for maximum accuracy. It’s fitted with a Ballistics Advantage barrel with a 1:7″ twist rate.

I built a retro AR-15 with a 20” barrel and 1:12” twist and fired 77-gr. bullets that perfectly keyholed the target because the rifling couldn’t stabilize the longer, heavier bullet. So, the bullet hit the target sideways. Accuracy is horrible with heavy bullets in that rifle. With 55-gr. bullets, however, that retro rifle with a 1:12 twist shoots the black out of the target. Rifling can also be too fast and over-stabilize the bullet causing the bullet to fragment in flight and lose all effectiveness.

heavy 223 bullets from 1 in 12 twist barrel
This is how 77-grain bullets perform in a 1:12 twist barrel; three perfect keyhole shots. The slow rifling did not stabilize the heavy bullet, causing the bullet to yaw and hit the target sideways.

When Eugene Stoner developed the AR-15, the idea was to use lightweight bullets in the 45- to 55-gr. range through a 20” barrel. Barrels were rifled in a slow 1:12” twist rate, capable of stabilizing lightweight bullets but not heavier bullets. Fast forward a few decades, and .223 bullets have evolved in bullet style, bullet material and weight. Today 75- and 77-gr. .223 bullets are just as common as 55- to 62-gr. bullets. Twist rate is your clue on what weight bullets will perform optimally in your gun. Some shooters might not think twice about the twist rate in their barrel, but if they knew that could fine-tune their bullet performance they might pay closer attention.

Twist Rate Sweet Spot

Most AR-15 rifles and carbines produced today use rifling with a 1:8 twist rate. In my opinion, a twist rate of 1:8 is perfect for a general-purpose, 16” barrel AR since this twist offers versatility and can easily stabilize both light and heavy bullets. In fact, the sweet spot for 1:8 bores are bullets weighing from 62 to 77 grains.

1 in 8 twist barrel
Most general purpose AR’s have a 1:8 twist rate, like this SAINT Victor. This is a versatile twist rate capable of handling bullets from 62 to 77 grains.

In the 1980s, when the U.S. military moved to the M16A2 rifle and the 62-gr. M855 cartridge, it chose a 1:7 twist rate that has become the de facto rifling in all U.S. military rifles and carbines chambered in 5.56 NATO. The change had to do with the 1:7 twist rate stabilizing heavier 70- to 77-gr. bullets and the rifling’s ability to stabilize tracer rounds. The 1:7 twist can stabilize bullets weighing up to 90 grains.

I had an engineering professor who was fond of saying, “Test them like you use them”. So, to prove out the thesis, I sat down at the range bench with a stock, off-the-shelf Springfield Armory ATC with its 1:7 twist rate for heavy bullets and mounted with a Leupold Patrol 6HD 1-6x24mm scope. I used Nosler cartridges since they provide a wide assortment of bullet weights, bullet material and bullet types — from lightweights like the Expansion Tip 55-gr. lead-free ET rounds and the Ballistic Tip 55-gr. BTV, to Match Grade 70-gr. RDF (Reduced Drag Factor), and the lunker in the bunch Match Grade 77-gr. HPBT.

Heavy Bullets, Small Groups

After running a bunch of orphan cartridges through the ATC — these are leftover rounds from training and testing — at 50 yards, I loaded up the hefty Nosler 77-gr. HPBT rounds and tweaked the zeroed at 100 yards. Those 77-gr. HPBTs gave me a muzzle velocity of 2,391 fps and a best three-shot group that was as big as my thumbnail and measured 0.39”.

nosler 77 gr match 223 ammo
Long-range shooting requires heavier bullets. Nosler’s 77-grain HPBT (Hollow Point Boat Tail) ammo is designed for competition and produced this 0.39″ group.

Moving to 70-gr. RDF rounds, my group opened up to 0.52”. All the heavier bullets were shooting sub-MOA. I tried the lighter 55-gr. rounds next. The 55-gr. all copper ET bullets provided a best group of 1.05” and deflated my balloon. My expectations were low with the 55-gr. BTV rounds, but I needed a screwdriver to remove the goofy grin after shooting a group that measured 0.34”.

55 grain bullet weight from 1 in 7 twist barrel
Varmint hunting rounds like the Nosler 55-grain BTV (Ballistic Tip Varmint) can still be used successfully in a 1:7 twist barrel. This group measures 0.34″.

Will this rifle shoot other 55-gr. ammo with the same accuracy? Maybe. Just know, the bullet weight’s sweet spot for a 1:7 twist rate is 69 grains and heavier. It will also shoot lighter bullets, but the accuracy may not be as good as it can be.

The Answer

What’s the answer to the best bullet weight for 1:7? In short, usually heavier bullets — but not always. Read the twist rate on modern AR barrels chambered in .223 Remington and 5.56 NATO you will most likely see: 1:9, 1:8 and 1:7. These are the most common twist rates on AR-15s produced today. Nearly all Springfield Armory SAINT series rifles have a 1:8 rifling twist rate designed to strike the best balance of accuracy and performance with the broadest range of bullet weights. But remember, the SAINT Edge ATC barrel has 1:7.

match the ammo to the barrel twist rate
Bullets of varying weights can be run through a 1:7” barrel. Heavier weights will be the best for the twist, while others will produce acceptable accuracy, just not optimal for the twist rate.

Pairing the proper bullet weight with the twist rate of your AR’s barrel means a better-stabilized bullet. It isn’t the silver bullet to accuracy (sorry couldn’t resist the pun), but it will get you down the right path to improved accuracy. You still need to put in some bench time trying different ammo brands. It’s not a guarantee to stellar accuracy, you will still need to run through ammo to understand what your particular rifle likes and what your barrel is capable of. Think about bullet weight and barrel twist rate when choosing ammunition for your AR, and try it out. You’ll likely find a loading that your particular rifle loves.

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Springfield Armory® recommends you seek qualified and competent training from a certified instructor prior to handling any firearm and be sure to read your owner’s manual. These articles and videos are considered to be suggestions and not recommendations from Springfield Armory. The views and opinions expressed on this website are those of the authors and do not necessarily reflect the views and opinions of Springfield Armory.

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Robert A. Sadowski

Robert A. Sadowski

Robert A. Sadowski has written about firearms and hunting for more than fifteen years. He has trained with some of the country’s finest firearm instructors in handguns, rifles/carbines, shotguns and long-range shooting. He is the author of numerous gun books, including 9MM — Guide to America's Most Popular Caliber, a #1 New Release on Amazon. He is a contributing editor to numerous gun-enthusiast magazines and websites, including Combat Handguns, Black Guns, Gun Tests, Gun Digest, Gun World, Ballistic,, SHOT Business, and others. He also edited Shooter’s Bible Guide to Firearms Assembly, Disassembly, and Cleaning; 50 Guns That Changed the World; and Gun Traders Guide.

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