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May 20th, 2022

How Muzzle Velocity Changes with Different Barrel Twist Rates

applied Ballistics Barrel Twist rate velocity testing test bryan Litz
Many barrel-makers mark the twist rate and bore dimensions on their barrel blanks.

Does muzzle velocity change with faster or slower barrel twist rates? Absolutely, but much less than you might think. Faster twist rates do slow down bullets somewhat, but the speed loss is NOT that significant. With Bartlein .308 Win barrels of identical length and contour, a 1:12″-twist barrel was only 8 fps faster than a 1:8″-twist barrel. That was the result of testing by Applied Ballistics.

The Applied Ballistics team tested six (6) same-length/same-contour Bartlein barrels to observe how twist rate might affect muzzle velocity. This unique, multi-barrel test is featured in the book Modern Advancements in Long Range Shooting, Vol. 1. That book includes other fascinating field tests, including a comprehensive chronograph comparison.

applied Ballistics Barrel Twist rate velocity testing test bryan Litz

applied Ballistics Barrel Twist rate velocity testing test bryan Litz
Barrel Twist Rate vs. Velocity — What Tests Reveal
by Bryan Litz
When considering barrel twist rates, it’s a common belief that faster twist rates will reduce muzzle velocity. The thinking is that the faster twist rate will resist forward motion of the bullet and slow it down. There are anecdotal accounts of this, such as when someone replaces a barrel of one brand/twist with a different brand and twist and observes a different muzzle velocity. But how do you know the twist rate is what affected muzzle velocity and not the barrel finish, or bore/groove dimensions? Did you use the same chronograph to measure velocity from both barrels? Do you really trust your chronograph?

Summary of Test Results
After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the average rate of approximately 1.33 FPS per inch of twist. In other words, your velocity is reduced by about 5 FPS if you go from a 1:12″ twist to a 1:8″ twist. — Bryan Litz

Savage Test Rifle with Six Bartlein Barrels
Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Most shooters don’t have access to the equipment required to fully explore questions like this. These are exactly the kinds of things we examine in the book Modern Advancements in Long Range Shooting, Vol. 1. In that book, we present experiments conducted in the Applied Ballistics lab. Some of those experiments took on a “Myth Buster” tone as we sought to confirm (or deny) popular pre-conceptions. For example, here’s how we approached the question of barrel twist and muzzle velocity.

Six .308 Win Barrels from Bartlein — All Shot from the Same Rifle
We acquired six (6) barrels from the same manufacturer (Bartlein), all the same length and contour, and all chambered with the same reamer (SAAMI spec .308 Winchester). All these barrels were fitted to the same Savage Precision Target action, and fired from the same stock, and bench set-up. Common ammo was fired from all six barrels having different twist rates and rifling configurations. In this way, we’re truly able to compare what effect the actual twist rate has on muzzle velocity with a reasonable degree of confidence.

Prior to live fire testing, we explored the theoretical basis of the project, doing the physics. In this case, an energy balance is presented which predicts how much velocity you should expect to lose for a bullet that’s got a little more rotational energy from the faster twist. In the case of the .30 caliber 175 grain bullets, the math predicts a loss of 1.25 fps per inch-unit of barrel twist (e.g. a 1:8″ twist is predicted to be 1.25 fps slower than a 1:9″ twist).

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied Ballistics

Above, data shows relationship between Twist Rate and Muzzle Velocity (MV) for various barrel twist rates and rifling types. From fast to slow, the three 1:10″ twist barrels are: 5R (canted land), 5 Groove, 5 Groove left-hand twist.

We proceeded with testing all 6 barrels, with twist rates from 1:8″ to 1:12″. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the average rate of approximately 1.33 fps per inch of twist. In other words, your velocity is reduced by about 5 fps if you go from a 1:12″ twist to a 1:8″ twist. [Editor: That’s an average for all the lengths tested. The actual variance between 1:12″ and 1:8″ here was 8 FPS.] In this case the math prediction was pretty close, and we have to remember that there’s always uncertainty in the live fire results. Uncertainty is always considered in terms of what conclusions the results can actually support with confidence.

Barrel Twist Rate Velocity Modern Advancements Book Bryan Litz Applied BallisticsThis is just a brief synopsis of a single test case. The coverage of twist rates in Modern Advancements in Long-Range Shooting Vol. 1 is more detailed, with multiple live fire tests. Results are extrapolated for other calibers and bullet weights. Needless to say, the question of “how twist rate affects muzzle velocity” is fully answered.

Other chapters in the book’s twist rate section include:
· Stability and Drag — Supersonic
· Stability and Drag — Transonic
· Spin Rate Decay
· Effect of Twist rate on Precision

Other sections of the book include: Modern Rifles, Scopes, and Bullets as well as Advancements in Predictive Modeling. This book is sold through the Applied Ballistics online store. Modern Advancements in Long Range Shooting is also available as an eBook in Amazon Kindle format.

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May 20th, 2022

CMP Awards 142 Scholarship Awards to Junior Shooters

CMP Shooting scholarships high school college 2022

The Civilian Marksmanship Program (CMP) has issued 142 scholarship grants to outstanding junior marksmen. The CMP Scholarship Program provides funds to gifted secondary students who will graduate from high school in 2022, and enroll in college in the fall of 2022.

CMP Shooting scholarships high school college 2022

CLICK HERE for Full List of Scholarship Winners »

CMP marksmanship college scholarshipsAlong with a generous $30,000 contribution from the Garand Collectors Association (GCA), the CMP awarded $178,000 in scholarships to remarkable young individuals from across the country. Of the applications received, the median grade point average was an incredible 4.05 — the highest in the history of the Scholarship program. Applicants came from 37 of the 50 states as well as military stations outside the USA. These scholarships will go towards college expenses for the collegiate term commencing in the fall of 2022.

Though most of the recipients received $1,000 scholarships, the CMP also provided $3,000 grants to 16 exceptional candidates with notable extra-curricular activities and/or community service as well as firm commitments to marksmanship. These special student-athletes each received $3,000 in funding. In addition, one $5,000 Carolyn Hines Memorial Scholarship was also awarded to the top overall applicant.

Top Young Marksman from Ohio Awarded $5000 Scholarship
The $5,000 Carolyn Hines Memorial Scholarship has been awarded to Johnathan Dorsten of Bryan, Ohio. Johnathan has committed to the Ohio State Pistol team for the upcoming school year.

Winners of $3,000 scholarships are: Phoebe Chandler (Parker, SD), Annie Downum (Springdale, AR), Sarah Folsom (Granbury, TX), Victoria James (Woodine, MD), Isaac Joback (Fenton, MO), Alexis Kunze (Oak Harbor, WA), Abbie Leverett (Bainbridge, GA), Chandler Livingston (Chula, GA), Molly Palko (Albuquerque, NM), Emma Rhode (Kempton, PA), Benjamin Rogers (Gardner, KS), Bryce Roop (Decatur, IN), Samuel Sparrow (Hendersonville, TN), Maria Tortorelli (APO), Hannah Vaagen (Devils Lake, ND), and Elysa Walter (Sugar Hill, GA).

cmp scholarship
Many of the scholarship winners learned their skills through youth air rifle programs.

To review all the scholarship recipients, view the CMP Scholarship Program Page. Congratulations to all these talented scholar-shooters. CLICK HERE for a spreadsheet listing all 2022 scholarship winners with their locations and shooting club affiliations.

Permalink News, Shooting Skills 1 Comment »
May 20th, 2022

Make Your Own Length-to-Lands Gauge — Quick & Easy

case OAL gauge home made

Here’s a tip we feature every year or so, because it is something that costs nothing, yet can be very useful in the reloading process. With a simple, easy modification to a fired case, you can determine the length to lands in your rifle barrel. As long as you set the tension right, the measurements should be repeatable, and you’ve just saved yourself $47.66 — the combined cost of a Hornady commercial OAL gauge ($42.00) and Modified Case ($5.66).

To achieve best accuracy with a rifle, you must control bullet seating depth very precisely, so all bullets end up in the same place relative to the entrance of the lands, every time. There may be multiple cartridge OALs which prove accurate. However, with each, you first need to determine a “zero” point — a reliable, and repeatable OAL where the bullet is “just touching” the lands.

There are tools, such as the Hornady (formerly Stoney Point) OAL Gauge, that will help you find a seating OAL just touching the lands. However, the tool requires that you use a special modified case for each cartridge you shoot. And, while we find that the Hornady OAL Gauge is repeatable, it does take some practice to get in right.

Make Your Own Length-to-Lands Gauge with a Dremel
Here’s an inexpensive alternative to the Hornady OAL tool — a slotted case. Forum member Andris Silins explais how to create a slotted case to measure length to the lands in your rifle:

“Here’s what I did to find length to lands for seating my bullets. I made four cuts into the neck of fire-formed brass. Then I pressed the bullet in lightly and chambered the entire gauge. As the cartridge chambers, the bullet slides back into the case to give you length to lands. It took less than five minutes to get it cut and working. A little light oil in the barrel just past the chamber helps ensure the bullet does not get stuck in the lands. It works great and is very accurate.

How to Adjust Tension — Length and Number of Neck Cuts
I made the cuts using a Dremel with a cut-off wheel. You can adjust tension two ways. First, you can make the cuts longer or shorter. Longer cuts = less tension. If you used only three cuts instead of four you would get more tension. The trick is to be gentle when you open and close the bolt. If you ram the bolt closed you may wedge the bullet into the lands. When you open the bolt it helps to keep a finger or two near by to guide the case out straight because the ejector wants to push it sideways.”

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