Initial radar testing shows an interesting stability trend for slugs vs. pellets: drag is minimized for pellets in slower-twist barrels, while drag of slugs is minimized for a faster twist. Also, consistency of drag/BC is best when drag is minimized (BC maximized).
Show below are test data for .300 caliber 44.5 grain Slug and .300 caliber 44.8 grain Pellet, both shot from an air rifle around 800 FPS. Experienced air rifle shooters told us to expect this so it’s nice to see the measurements supporting this trend!
So why is fast twist good for slugs while bad for pellets and vice versa? Air rifle pellets with a skirt are mostly drag-stabilized, not spin-stabilized. So, they don’t need much if any spin at all to fly point forward; the skirt catches the air like the fins of a rocket. As such, spinning the pellets faster only becomes a problem of dynamic stability. If I had any suggestion after looking at this data, it would be to try an even slower twist for pellets, perhaps a 1:60″ (one turn in 5 feet) or even 1:120″.
Slugs are spin-stabilized so it reasons that more spin suppresses yaw and maximizes BC, to a point. Based on these results, it appears the slug is reaching max stability/BC with the 1:22″ and the 1:18″ provides no further benefit. Again, these are just initial findings, we’re eager to explore further in the coming weeks! To view our recent Air Rifle projectile testing, with full 8-minute video, CLICK HERE.
This report is from Bryan Litz and the ScienceofAccuracy.com website.
As long as there have been rifles, there has been a debate as to how much – if any – the rifle moves prior to the bullet exiting the bore. The first video below shows a Barrett MRAD chambered in .338 Lapua Magnum firing a 300gr Lapua Scenar bullet. Capturing projectiles at 100k+ frames per second allows us to visualize aspects of the firing sequence that are otherwise invisible to the human eye.
Click Video to see barrel with suppressor (on right) move with recoil before bullet exits.
What is clear from this video is that the rifle system is moving rearward while the bullet is traveling through barrel and subsequently through the suppressor. During the “in-bore” portion of bullet travel, any deviation of the muzzle orientation from the initial point of aim can cause a point of impact change. This is because the bullet will exit while the barrel is pointed somewhere different than when the shot was initially fired. Much of the shot’s point-of-aim orientation can be maintained through consistent marksmanship fundamentals and recoil management techniques. However, most shooters are not likely capable of managing it to less than 0.001″ for EVERY shot, especially given on lightweight magnum rifles.
Here’s another example with a 180gr bullet in a Rem 700 BDL .30-06 rifle. “Every time we watch a video like this it reminds us that guns like this, the majority of accuracy and precision come from the gun/sight/support system, not the ammo. When you consider that 0.005″ of muzzle deflection, (orthogonal to the bore) results in ~1.5 moa of dispersion (.75 in any direction) and you see this massive barrel movement prior to bullet exit, it’s clear that the vast majority of dispersion [for typical rifles] is coming from this movement”.
Precision rifle systems, such as benchrest, PRS, and F-Class rifles, tend to minimize the movement away from the bore axis prior to bullet exit to achieve the best possible precision. A common theme among the most precision systems is higher-weight rifles with lower-weight projectiles. This relates to basic physics: Newton’s Third of Motion “For every action, there is an equal and opposite reaction.” With all else held equal, if the rifle weighs more and the bullet weighs less, there is a lower magnitude of motion prior to the bullet leaving the barrel.
In our latest book, Modern Advancements in Long Range Shooting Volume III, Chapter 3 covers the Theory of Precision for Rifles which mathematically describes and estimates the precision potential of rifles based on rifle mass and kinetic energy of the bullet. The chapter includes all the live fire test data to support the theory and great discussion on the testing performed can be found on our podcast at the Science of Accuracy Academy website.
Applied Ballistics has just launched a great, new online resource for shooters: The Science of Accuracy Academy. This subscription-based website is launching with nearly 30 podcast episodes, with many more planned, as well as video content, Zoom classes, and much more.
The main goal of this new online resource is to adapt and modernize the delivery of content coming from Applied Ballistics LLC. In past years, books, DVDs, and seminars were the primary avenues for delivering information. Modern technology has evolved, and the delivery of information can be done in more efficient ways such as streaming videos, podcast discussions of book and seminar content. In addition to being a more modern delivery platform, The Science of Accuracy Academy allows for more frequent updates than traditional books and DVDs.
Bryan Litz, owner of Applied Ballistics LLC tells us: “I’m very excited about this avenue to share what we’re learning in the Applied Ballistics lab. I think many shooters will benefit from the podcasts, which contain very insightful discussions and can be enjoyed in your car, or as you work. We look forward to publishing more of our research thru the Science of Accuracy Academy”.
About the Science of Accuracy Academy Content and Programs
Below, Bryan Litz comments about the Academy’s new podcast offerings and other interactive content. Bryan notes: “We’ve benefited a great deal from practicing the scientific method, and we want to share what we’ve learned.”
Book Content via Podcasts — Many of the podcast episodes are specific reviews of Applied Ballistics book chapters. I’ll sit with Mitch or Francis (both experienced, champion shooters) and discuss the chapter, what it was like to do the tests. We will also discuss behind the scenes problems, as well as what we’ve learned since publishing the books. This lets subscribers get knowledge from the books. And, as a podcast, you can listen while driving, working out, or whatever.
The World of Doppler Radar — In recent years we have spent considerable time visiting shooting matches with the AB Mobile Lab and running Doppler radar. Between that and some of the government contracting work, we’ve built up a lot of experiences and it’s been a long time since a book was published. This Academy is a great outlet for us to update the shooting world on what we’ve been doing and learning.
Ballistics Science and Precision Loading — We’ve been doing hardcore ballistic science for the past few years and have a lot to share. We’ve come to see some aspects of handloading and shooting in a fundamentally different way. For example, understanding the statistical nature of precision has caused us to re-shape how we make decisions in the handloading process. As a result, we now better understand cause-effect relationships and can make deliberate, reliable progress as a result.
Bryan Litz Announces the New Science of Accuracy Academy
The Lighter Side — Bryan told AccurateShooter.com: “Some of the podcast episodes are much less serious! We have fun arguing about which shooting disciplines are harder. For example, Mitch Fitzpatrick and I talk with Francis Colon and Chad Heckler about PRS vs. ELR shooting. We discuss what we like and dislike about the different sports, what we would like to see changed, and what competition shooting has meant for us as individuals. This open-ended format explores long range shooting from the technical to the personal and everything in-between.”
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