October 1st, 2015

The Transonic Zone — What Happens to Bullet Stability and BC

These four photos show the substantial changes in the shock wave and turbulence patterns for the same 7.5mm bullet at different velocities. The “M” stands for Mach and the numerical value represents the velocity of the bullet relative to the speed of sound at the time of the shot. Photos by Beat Kneubuehl.

“Going transonic” is generally not a good thing for bullets. The bullet can lose stability as it enters the transonic zone. It can also become less slippery, losing BC as a consequence of dynamic instability. In this video, Bryan Litz of Applied Ballistics analyzes what happens to bullet stability (and BC) as projectiles approach the speed of sound. Transonic effects come into play starting about Mach 1.2, as the bullet drops below 1340 fps.

Transonic Ballistics Effects Explained by Bryan Litz
What happens when the bullet slows to transonic speed, i.e. when the bullet slows to about 1340 feet per second? It is getting close to the speed of sound, close to the sound barrier. That is a bad place to fly for anything. In particular, for bullets that are spin-stabilized, what the sound barrier does to a bullet (as it flies near Mach 1) is that it has a de-stabilizing effect. The center of pressure moves forward, and the over-turning moment on the bullet gets greater. You must then ask: “Is your bullet going to have enough gyroscopic stability to overcome the increasing dynamic instability that’s experienced at transonic speed?”

Some bullets do this better than others. Typically bullets that are shorter and have shallow boat-tail angles will track better through the transonic range. On the contrary, bullets that are longer… can experience a greater range of pitching and yawing in the transonic range that will depress their ballistic coefficients at that speed to greater or lesser extents depending on the exact conditions of the day. That makes it very hard to predict your trajectory for bullets like that through that speed range.

When you look at transonic effects on stability, you’re looking at reasons to maybe have a super-fast twist rate to stabilize your bullets, because you’re actually getting better performance — you’re getting less drag and more BC from your bullets if they are spinning with a more rigid axis through the transonic flight range because they’ll be experiencing less pitching and yawing in their flight.

Bryan Litz Applied Ballistics Transonic Twist Rate Stability

To determine how bullets perform in the “transonic zone”, Bryan did a lot of testing with multiple barrels and various twist rates, comparing how bullets act at supersonic AND transonic velocities. Bryan looked at the effect of twist rates on the bullets’ Ballistic Coefficient (BC). His tests revealed how BC degrades in the transonic zone due to pitching and yawing. Bryan also studied how precision (group size) and muzzle velocity were affected by twist rates. You may be surprised by the results (which showed that precision did not suffer much with faster barrel twist rates). The results of this extensive research are found in Bryan’s book Modern Advancements in Long Range Shooting.

Bryan notes: “A lot of gunpowder was burned to get these results and it’s all published in layman’s terms that are easy to understand”. If you’re interested in learning more about transonic bullet stability, you may want to pick up a copy of Bryan’s book.

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October 1st, 2015

Gun Trader’s Guide (37th Edition) Just Released

Gun Trader 37th Edition gun valuesThe new, 37th Edition of the Gun Trader’s Guide has just been released. This fully-illustrated resource features current market values for thousands of rifles, pistols, and shotguns. This 37th Edition, now with over 1000 photographs, includes dozens of new entries added since the previous edition. Along with the Blue Blue of Gun Values, the Gun Trader’s Guide is one of the two definitive resources on gun prices. If you buy or sell firearms, the Gun Traders’ Guide is a must-have item that will pay for itself. Over two million copies of the Gun Trader’s Guide have been sold to date. Order soon to be one of the first to own the new 37th Edition. Amazon’s price is $23.24.

If you don’t want to lug the big book around, a Kindle (electronic) Edition of the 2014 Gun Trader’s Guide to Rifles is available for just $16.17. This 608-page eBook edition of the 2014 Guide can be viewed on a Kindle, iPad, laptop, or your home computer. This is handy if you want to access gun values at a gunshop, estate sale, or auction.

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October 1st, 2015

Field Test of Nightforce SHV by LongRangeHunting.com

If you’ve been considering the new Nightforce SHV scope for a hunting application, head over to LongRangeHunting.com. There you’ll find an in-depth field test of the 4-14x56mm SHV by Nicholas Gebhart. This is a very thorough review — Gebhardt checks every feature of the scope and comparison tests the SHV against the more costly Nightforce NXS 3.5-15x50mm. Gebhardt even put the SHV scope in his freezer for a weekend to ensure there was no fogging.

NXS SHV scope review long range huntingOverall, Gebhardt was very pleased with the SHV: “Optical clarity, image brightness, contrast and resolution were all extremely good.” The tester also liked the MOAR reticle in his scope. He didn’t think it was too “busy” though he thought the hold-over lines would benefit from numbers: “Nightforce’s MOAR was easy to use and provided a clear sight picture for engaging small targets. The line thickness is perfect for both precise shot placement and visibility. My personal preference however would be for the even hash marks to be numbered for the entire lower portion of the reticle.” Gebhart noted that the SHV’s side parallax knob had yardage marking numbers that proved accurate (and handy to use) — most other scopes just have lines.

Nightforce SHV vs. Nighforce NXS
How did the new SHV stack up against the NXS in a side-by-side comparison? Gebhardt was impressed with the $995.00 SHV, saying it held its own with the pricier NXS model: “I took about 30 minutes to evaluate the optics of the SHV and see how it compared to an older Nightforce NXS 3.5-15X50. Both of these scopes are made in Japan but given the price differential, I expected to see some difference in the optical quality. To my surprise, I couldn’t find any optical difference between the two except for a very slight possibility of a brighter image with the SHV.”

Nicholas Gebhardt longrangehunting.com Nightforce SHV review

CLICK HERE to Read Full Nightforce SHV Scope Review.

View Nightforce SHV 4-14x56mm Specs in Long-Range Hunting Store ($975.00).

Nicholas Gebhardt has been an active hunter primarily pursuing mule deer, antelope, coyotes and prairie dogs since he was old enough to legally hunt. Nicholas is also a precision rifle competitor and a Captain in the Montana National Guard.

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