As an Amazon Associate, this site earns a commission from Amazon sales.











August 16th, 2021

Bullets Spinning Fast Enough? Use Berger Twist Rate Calculator

Berger twist rate calculator

Berger Twist-Rate Stability Calculator
Berger twist rate calculatorOn the Berger Bullets website you’ll find a handy Twist-Rate Stability Calculator that predicts your gyroscopic stability factor (SG) based on mulitiple variables: velocity, bullet length, bullet weight, barrel twist rate, ambient temperature, and altitude. This cool tool tells you if your chosen bullet will really stabilize in your barrel.


CLICK HERE to Go to TWIST RATE CALCULATOR PAGE »

How to Use Berger’s Twist Rate Calculator
Using the Twist Rate Calculator is simple. Just enter the bullet DIAMETER (e.g. .264), bullet WEIGHT (in grains), and bullet overall LENGTH (in inches). On its website, Berger conveniently provides this info for all its bullet types. For other brands, we suggest you weigh three examples of your chosen bullet, and also measure the length on three samples. Then use the average weight and length of the three. To calculate bullet stability, simply enter your bullet data (along with observed Muzzle Velocity, outside Temperature, and Altitude) and click “Calculate SG”. Try different twist rate numbers (and recalculate) until you get an SG value of 1.4 (or higher).

Gyroscopic Stability (SG) and Twist Rate
Berger’s Twist Rate Calculator provides a predicted stability value called “SG” (for “Gyroscopic Stability”). This indicates the Gyroscopic Stability applied to the bullet by spin. This number is derived from the basic equation: SG = (rigidity of the spinning mass)/(overturning aerodynamic torque).

Berger twist rate calculator

If you have an SG under 1.0, your bullet is predicted not to stabilize. If you have between 1.0 and 1.1 SG, your bullet may or may not stabilize. If you have an SG greater than 1.1, your bullet should stabilize under optimal conditions, but stabilization might not be adequate when temperature, altitude, or other variables are less-than-optimal. That’s why Berger normally recommends at least 1.5 SG to get out of the “Marginal Stability” zone.

In his book Applied Ballistics For Long-Range Shooting (3rd Ed.), Bryan Litz (Berger Ballistician) recommends at least a 1.4 SG rating when selecting a barrel twist for a particular bullet. This gives you a safety margin for shooting under various conditions, such as higher or lower altitudes or temperatures.

Story idea from EdLongrange. We welcome reader submissions.
Permalink - Articles, Bullets, Brass, Ammo, Reloading, Tech Tip 2 Comments »
June 22nd, 2021

AR Platform Video Series from Brownells — Watch and Learn

Brownelss tech tip video AR15 ar platform rifle gunsmithing

Do you own or shoot an AR-platform “black rifle”? Then you know these rifles run dirty, and have some unusual maintenance requirements. On the other hand, the AR “Modern Sporting Rifle” is fun and versatile with a vast range of options among buttstocks, barrels, handguards, and grips. You can assemble a simple 16″ barrel .223 Rem rig for home defense, or build a long-barreled 6mm ARC rifle with bag-rider buttstock and high-magnification optic for long range target work. The choice is up to you.

To help with your black rifle journey, here are four helpful videos from Brownells. These will help ensure your AR rifle cycles reliably and runs longer, with reduced wear. Brownells also explains how to choose the optimal barrel twist rate. CLICK HERE to order AR parts, accessories, and ammo from Brownells.

AR Bolt/Bolt Carrier Lubrication — Smarter Methods

This video shows the proper way to lubricate an AR-15 bolt-carrier assembly. The video identifies the key metal-on-metal friction points where you actually need lubrication: the rails on the underside of the carrier, shiny wear points on top, and just a dab on the cam pin. How much oil/lubricant should you use? The AR-15 is pretty forgiving on that point. Some spots work best with grease, others work best with a lighter oil. Just keep it out of the combustion areas. Those little holes in the carrier are gas vent holes, NOT oil holes!

AR Barrel Twist Rates — What You Need to Know

AR barrels can be ordered with a variety of twist rates from 1:12″ to 1:7″. Basically, the longer/heavier the bullet you plan to shoot, the faster the twist rate you need. For example, Sierra recommends a 1:7″ twist rate for the 90gr SMK. A 1:12″ could work with the small lightweight bullets up to 55 grains. The 1:9″ barrel will stabilize the light and mid-weight bullets up to about 77 grains. We recommend a 1:8″ or 1:7″ twist rate for the best versatility. You’ll find a detailed discussion of AR twist rates on PewPewTactical.com.

Barrel Gas Block Alignment — Key to Reliable Cycling

In this Tech Tip, Brownells gun tech Steve Ostrem explains surefire methods to align your gas block. The most common problem with AR builds is poor cycling, commonly caused by misalignment between the gas block and the barrel’s gas port.

Setting Up Gas Tube Systems

This Tech Tip examines AR-platform gas systems, and shows how to select the proper length gas tube, and how to configure multiple tube systems if you change your barrel to different lengths. This is worth watching for anyone re-barreling an AR.

Permalink - Articles, - Videos, Gunsmithing, Tactical No Comments »
December 1st, 2019

Common Misconceptions about Twist Rate and Stabilization

FirearmsID.com barrel rifling diagram

Understanding Twist: Bullet Stabilization

by Sierra Bullets Ballistic Technician Paul Box for Sierra Bullets Blog.

Based on the questions we get on a daily basis on our 800 (Customer Support) line, twist is one of the most misunderstood subjects in the gun field. So let’s look deeper into this mystery and get a better understanding of what twist really means.

When you see the term 1:14″ (1-14) or 1:9″ twist, just exactly what does this mean? A rifle having a 1:14″ twist means the bullet will rotate one complete revolution every fourteen inches of the barrel. Naturally a 1:9″ turns one time every nine inches that it travels down the barrel. Now, here’s something that some people have trouble with. I’ve had calls from shooters thinking that a 1:14″ twist was faster than a 1:9″ because the number was higher with the 1:14″. The easiest way to remember this is the higher the number, the slower the twist rate is.

Now, the biggest misconception is that if a shooter has a .223 with a 1:8″ twist, his rifle won’t stabilize a 55gr bullet or anything lighter. So let’s look at what is required. The longer a bullet is for its diameter, the faster the twist has to be to stabilize it. In the case of the .223 with a 1:8″ twist, this was designed to stabilize 80gr bullets in this diameter. In truth the opposite is true. A 1:8″ will spin a 55gr faster than what is required in order to stabilize that length of bullet. If you have a bullet with good concentricity in its jacket, over-spinning it will not [normally] hurt its accuracy potential. [Editor’s Note: In addition, the faster twist rate will not, normally, decrease velocity significantly. That’s been confirmed by testing done by Bryan Litz’s Applied Ballistics Labs. There may be some minor speed loss.]

FirearmsID.com barrel rifling diagram
Many barrel-makers mark the twist rate and bore dimensions on their barrel blanks.

Think of it like tires on your truck. If you have a new set of tires put on your truck, and they balance them proper at the tire shop, you can drive down a street in town at 35 MPH and they spin perfect. You can get out on the highway and drive 65 MPH and they still spin perfect. A bullet acts the same way.

Once I loaded some 35gr HP bullets in a 22-250 Ackley with a 1:8″ twist. After putting three shots down range, the average velocity was 4584 FPS with an RPM level of 412,560. The group measured .750″ at 100 yards. This is a clear example that it is hard to over-stabilize a good bullet.

Twist-rate illustration by Erik Dahlberg courtesy FireArmsID.com. Krieger barrel photo courtesy GS Arizona.
Permalink - Articles, Bullets, Brass, Ammo 3 Comments »
September 18th, 2019

Too Fast or Too Slow — What’s Your Optimal Twist Rate?

Glen Zediker Twist Rate .223 Rem Barrel Top Grade Ammo Midsouth
Here’s an extreme range of .224-Caliber bullets: 35gr varmint bullet and 90gr match bullet. Of course, along with bullet length/design, you need to consider MV when choosing twist rate.

Even with the same caliber (and same bullet weight), different bullet types may require different rates of spin to stabilize properly. The bullet’s initial spin rate (RPM) is a function of the bullet’s muzzle velocity and the spin imparted by the rifling in the barrel. You want to ensure your bullet is stable throughout flight. It is better to have too much spin than too little, according to many ballistics experts, including Bryan Litz of Applied Ballistics. Glen Zediker has some basic tips concerning barrel twist rates and bullet stability. These come from his latest book, Top Grade Ammo.

Choosing the Right Twist Rate
I’d always rather have a twist too fast than not fast enough. Generally… I recommend erring toward the faster side of a barrel twist decision. 1:8″ twist is becoming a “new standard” for .224 caliber, replacing 1:9″ in the process. The reason is that new bullets tend to be bigger rather than smaller. Don’t let a too-slow twist limit your capacity to [achieve] better long-range performance.

Base your next barrel twist rate decision on the longest, heaviest bullets you choose to use, and at the same time realize that the rate you choose will in turn limit your bullet choices. If the longest, heaviest bullet you’ll shoot (ever) is a 55-grain .224, then there’s honestly no reason not to use a 1:12″. Likewise true for .308-caliber: unless you’re going over 200-grain bullet weight, a 1:10″ will perform perfectly well.

Glen Zediker Twist Rate .223 Rem Barrel Top Grade Ammo Midsouth

Bullet Length is More Critical than Weight
Bullet length, not weight, [primarily] determines how much rotation is necessary for stability. Twist rate suggestions, though, are most usually given with respect to bullet weight, but that’s more of a generality for convenience’s sake, I think. The reason is that with the introduction of higher-ballistic-coefficient bullet designs, which are longer than conventional forms, it is easily possible to have two same-weight bullets that won’t both stabilize from the same twist rate.

Evidence of Instability
The tell-tale for an unstable (wobbling or tumbling) bullet is an oblong hole in the target paper, a “keyhole,” and that means the bullet contacted the target at some attitude other than nose-first.

Glen Zediker Twist Rate .223 Rem Barrel Top Grade Ammo MidsouthIncreasing Barrel Length Can Deliver More Velocity, But That May Still Not Provide Enough Stability if the Twist Rate Is Too Slow
Bullet speed and barrel length have an influence on bullet stability, and a higher muzzle velocity through a longer tube will bring on more effect from the twist, but it’s a little too edgy if a particular bullet stabilizes only when running maximum velocity.

My failed 90-grain .224 experiment is a good example of that: I could get them asleep in a 1:7″ twist, 25-inch barrel, which was chambered in .22 PPC, but could not get them stabilized in a 20-inch 1:7″ .223 Rem. The answer always is to get a twist that’s correct.

These tips were adapted from Glen’s newest book, Top-Grade Ammo, available at Midsouth. To learn more about this book and other Zediker titles, and read a host of downloadable articles, visit ZedikerPublishing.com.

Permalink - Articles, Bullets, Brass, Ammo, Tech Tip 1 Comment »