The U.S. Army Marksmanship Unit (USAMU), in cooperation with Shooting USA TV, has created a series of instructional Pro Tip pages covering a wide range of shooting disciplines. All totaled, there are more than 50 USAMU Pro Tips. Most relate to rifle marksmanship but there are also numerous tips for shotgunners and pistol shooters. Each Pro Tip entry includes multiple photos and 6-15 paragraphs, in an easy-to-follow format. Many Pro Tips also include an instructional video produced by Shooting USA. Here are three Pro Tip videos, and links to seven more Pro Tip web pages.
USAMU TOP TEN PRO TIPS
1. Reading the Wind with SGT Sherri Gallagher.
Apart from gravity, wind has the most pull on the bullet as it travels down range. Being able to accurately read the wind and mirage will greatly enhance your performance on the rifle range. National Champion, SGT Gallagher gives you some of her tips.
2. Angle Shooting with SFC (Ret.) Emil Praslick.
SFC Praslick shows you how to determine the angle to your target, and then how to include that to change your data necessary to hit your target on the first shot.
3. Rifle Grip, Stance and Body Position for 3-Gun with SFC Daniel Horner.
Professional 3-gun marksman SFC Daniel Horner, U.S. Army Marksmanship Unit (USAMU), give tips on how to properly handle a semi-automatic rifle, including grip, stance and body position.
We will be interviewing Bryan Litz of Applied Ballistics tomorrow at SHOT Show in Las Vegas. As a sneak preview of some of the topics we’ll cover, here are some highlights of some important, original research conducted by Bryan and his Applied Ballistics team. Bryan wanted to know how much velocity was altered by twist rate. The “real world” test results may surprise you….
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. That book includes many other fascinating field tests, including a comprehensive chronograph comparison.
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?
Savage Test Rifle with Six Bartlein Barrels
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. 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).
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 the testing in all 6 barrels from 1:8” to 1:12”. After all the smoke cleared, we found that muzzle velocity correlates to twist rate at the 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 a surprising number — much less than most folks would predict.] 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.
This is just a brief synopsis of a single test case. The coverage of twist rates in Modern Advancements in Long-Range Shooting 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 in eBook format in the Amazon Kindle store.
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Sometimes you’ll get a barrel that doesn’t stabilize bullets the way you’d anticipate, based on the stated (or presumed) twist rate. A barrel might have 1:10″ stamped on the side but it is, in truth, a 1:10.5″ twist or even a 1:9.5″. Cut-rifled barrels, such as Kriegers and Bartleins, normally hold very true to the specified twist rate. With buttoned barrels, due to the nature of the rifling process, there’s a greater chance of a small variation in twist rate. And yes, factory barrels can be slightly out of spec as well.
Before you purchase a bunch of bullets and set off to develop loads it’s wise to determine the true twist rate of your new barrel. Sinclair International, in its Reloading Press Blog provides a simple procedure for determining the actual twist rate of your barrel. Read on to learn how….
How Twist Rate Affects Bullet Stability
Most of you know that the twist of the rifling in the barrel is what puts spin on the bullet. As a bullet is pushed down the barrel and compressed into the rifling, the bullet follows the path or twist of the rifling. The combination of velocity and bullet spin is what stabilizes the bullet. Finding the twist rate for your barrel will help you in selecting appropriate weight bullets for your firearm. Remember, the general rule is that the faster the twist rate for a given caliber, the longer the bullet (of that caliber) you will be able to stabilize. (Generally speaking, a longer bullet will also be a heavier bullet, but the bullet geometry dictates the needed twist rather than the weight per se.)
Determining Barrel Twist Rate Empirically
Twist rate is defined as the distance in inches of barrel that the rifling takes to make one complete revolution. An example would be a 1:10″ twist rate. A 1:10″ barrel has rifling that makes one complete revolution in 10 inches of barrel length. Rifle manufacturers usually publish twist rates for their standard rifle offerings and custom barrels are always ordered by caliber, contour, and twist rate. If you are having a custom barrel chambered you can ask the gunsmith to mark the barrel with the twist rate.
Sinclair’s Simple Twist Rate Measurement Method
If are unsure of the twist rate of the barrel, you can measure it yourself in a couple of minutes. You need a good cleaning rod with a rotating handle and a jag with a fairly tight fitting patch. Utilize a rod guide if you are accessing the barrel through the breech or a muzzle guide if you are going to come in from the muzzle end. Make sure the rod rotates freely in the handle under load. Start the patch into the barrel for a few inches and then stop. Put a piece of tape at the back of the rod by the handle (like a flag) or mark the rod in some way. Measure how much of the rod is still protruding from the rod guide. You can either measure from the rod guide or muzzle guide back to the flag or to a spot on the handle. Next, continue to push the rod in until the mark or tape flag has made one complete revolution. Re-measure the amount of rod that is left sticking out of the barrel. Use the same reference marks as you did on the first measurement. Next, subtract this measurement from the first measurement. This number is the twist rate. For example, if the rod has 24 inches remaining at the start and 16 inches remain after making one revolution, you have 8 inches of travel, thus a 1:8 twist barrel.
This rifling illustration was created by Danish graphic artist Erik Dahlberg. It is published here courtesy FireArmsID.com, an excellent website for forensic firearms examiners.
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Choosing the right-diameter bullet can have a big effect on accuracy in match rifles. “Wait a minute”, you might say, “doesn’t one simply choose a 6mm bullet for a 6mm barrel and a 7mm bullet for a 7mm barrel, what’s the big deal?” Well… it’s not that simple. Not all bullets of the same nominal caliber actually have the same true diameter. We’ve seen different-brand 6mm bullets vary by as much as a full thousandth (.001″) in diameter. We have seen undeniable evidence that a poor “fit” of bullet diameter to bore dimensions can result in a poor-shooting gun, even one with a high-grade barrel.
Conversely, if you find the bullet diameter you barrel likes, that may instantly improve your accuracy. The accuracy gain may be more significant than making changes to the bullet seating depth or even powder charge. The importance of bullet diameter is compounded by the fact that 6mm match barrels are available with both .236″ and .237″ land diameters. Some barrels prefer “fat” bullets while other barrels prefer “skinny” bullets.
Last year, Jason Baney measured 12 different sets of 6mm Match Bullets, including a couple different lots of the same bullet design. Interestingly, Jason did measure the “old” Berger 105 VLD, the new-generation Berger 105 VLD (first lot from the new die), and the “new, improved” Berger 105 VLD from the new die, after it was polished. Ten (10) Bullets were measured per type. Each bullet was measured three times (3X) around the largest circumference, normally where a pressure ring would be located (some bullets have a pronounced pressure ring, others do not). NOTE: We provide the numbers from Jason’s tests, but remember that bullets from different production runs may have slightly different dimensions. You should augment our findings with your own measurements from later-produced bullets.
The first two columns of the chart show the smallest and largest bullet diameters measured for each 10-bullet sample. The third column shows the extreme spread over each 10-bullet set. Note, these numbers are NOT averages, but represent the “low” and “high” diameters for each set. (FYI: Jason noted that while the Lapua Scenars were very consistent, an earlier 2005 “JEVDAK” lot had smaller meplats than 2007 and 2008 lots.) A Mitutoyo Micrometer was used, zero-checked for each bullet.
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Krieger Barrels, respected maker of cut-rifled match and hunting barrels, announced it will offer 5R rifling for 6mm, 6.5mm, 7mm, and .308 caliber barrels. This kind of rifling features 5 lands and 5 grooves, but the lands are angled (slanted) on the sides (rather than 90°) for a gentler transition between land and groove. Krieger’s 5R rifling slants BOTH the leading and trailing edge of the lands (unlike “ratchet” rifling which is angled on one side only). 5R rifling also places each land opposite a groove. Having lands opposing grooves, along with slanted sides on the lands, is thought to give a better gas seal and reduced fouling. Additionally, some folks believe 5R rifling reduces jacket deformation by displacing less jacket metal. Overall, proponents of 5R rifling say it helps a barrel foul less and deliver more velocity than conventional rifling.
5R rifling will add $30 to the cost of a Krieger barrel. Krieger will NOT offer 5R rifling for gas gun barrels. Additionally, 5R rifling is offered only for constant twist-rate barrels. So, you can NOT get a gain twist barrel with 5R rifling. At this time 5R rifling is limited to 6mm, 6.5mm, 7mm, and 30 caliber bores, as listed in Krieger’s official announcement:
“Thanks to approval by Boots Obermeyer, Krieger Barrels, Inc. is now offering the true Obermeyer 5-R rifling pattern as an option on limited calibers with our barrels. We are very proud of the fact that Krieger Barrels was chosen as the only Obermeyer-approved maker of his style of 5-R rifling in North America. At this time we are limiting the 5-R option to the calibers listed below, but may offer others in the future as greater demand arises. There is a $30.00 up-charge to the base cost of the barrel for 5-R rifling. Currently available calibers:
5-R rifling is ONLY available in standard bore/groove dimensions listed and standard twist rates at this time. Please call if you have questions about availability of a certain caliber/twist combination. Please note, we are not, and have no plans to offer 5-R rifling in our finished ‘Gas Gun’ lines of M14, M1 Garand, AR-15, and AR-10 variants.”
5R Rifling in Production Guns
In the past, limited runs of Remington 700 tactical rifles, including some LE and SS (stainless special) models, have been offered with factory hammer-forged 5R barrels. These rifles have a reputation for shooting faster and more accurately than Rem 700s with conventional factory barrels. The Remington 5R barrels, though based on Obermeyer designs and similar to Mike Rock 5R barrels produced for the Army’s M24 sniper rifles, are NOT cut-rifled, but are produced in-house using the hammer-forging process.
Thompson/Center (T/C) Icon and Venture rifles currently feature 5R factory barrels. On T/C 5R barrels, the sides of each land are cut at a 65° angle vs. a 90° angle for standard rifling. See diagram. T/C claims that “because the edges of each land do not cut into and deform the bullet jacket… there will be less jacket fouling in the grooves”. T/C says this produces “greater bullet stability over multiple shots, and ultimately a rifle that’s easier to clean[.]”
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Sometimes you’ll get a barrel that doesn’t stabilize bullets the way you’d anticipate, based on the stated (or presumed) twist rate. A barrel might have 1:10″ stamped on the side but it is, in truth, a 1:10.5″ twist or even a 1:9.5″. Cut-rifled barrels, such as Kriegers and Bartleins, normally hold very true to the specified twist rate. With buttoned barrels, due to the nature of the rifling process, there’s a greater chance of a small variation in twist rate. And yes, factory barrels can be slightly out of spec as well.
