January 18th, 2016

Bargain Finder 18: AccurateShooter’s Deals of the Week

Accurateshooter Bargain Finder Deals of Week

At the request of our readers, we have launched a “Deals of the Week” feature. Every Monday morning we offer our Bargain selections. Here are some of the best deals on hardware, reloading components, and shooting accessories. Be aware that sale prices are subject to change, and once clearance inventory is sold, it’s gone for good. You snooze you lose.

1. Midsouth — Vortex Diamondback Scopes under $200.00

Vortex scopes are probably the most popular optics used by Precision Rifle Series competitors. The reason is that Vortex optics offer good performance and great value for money. Here’s a killer deal on mid-power variable Vortex scopes suitable for hunting or plinking rifles. The Vortex Diamondbacks are very rugged, and are supported by a no-BS Lifetime warranty.

2. Natchez — RCBS Special-5 Reloading Kit

Cabelas clearance case gun AR15

This kit is easily worth the $199.99 just for the press, primer tool, and powder measure (not to mention all the other stuff you get). We like the compact Reloader Special press as a secondary press for range use or special tasks such as bullet-pointing. This $199.99 RCBS Kit (which qualifies for a $10.00 RCBS Rebate) includes: Reloader Special-5 Press, Uniflow Powder Measure, RCBS Priming Tool, RCBS Loading Block, Deburring Tool, RCBS Powder Trickler, Powder Measure Stand, Funnel, and Nosler Loading Manual. Even if you already own a basic reloading press, this Kit is a great overall value.

3. MidwayUSA — Sierra BlitzKing Bullets, $105.99 for 500

MidwayUSA Sierra blitzking bullets

Varmint slayers rejoice. Here is a super deal on Sierra’s plastic-tipped BlitzKing bullets. Right now you can get 500 BlitzKing bullets for just $105.99. Get this low price on the .204-caliber 39gr boattail, or the .224-caliber 50- or 55-grain boattails. MidwayUSA also has other Sierra BlitzKing Bullets on sale, with big saving off the regular price. For example, the 6mm, 70gr BlitzKing is now just $134.99 for 500.

4. Cabela’s — Combo Tactical Hard Case and Soft Case Duo

Cabelas clearance case gun AR15

Get two (2) cases for the price of one. Here’s a sweet clearance deal from Cabelas.com. Right now you can get a tactical hard case PLUS a padded nylon soft case for just $79.88 (marked down from $119.99). The hard case measures 36″L x 13.25″W x 4.5″ on the inside. It features a high-density foam interior plus 4 steel external latches. The soft case features a water-resistant polyester shell and polyester lining.

5. MidwayUSA — Norma .22 LR Rimfire Ammo on Sale

MidwayUSA Norma .22 LR rimfire ammo Tac 22 Match 22

This Norma .22 LR rimfire ammo is good stuff. We’ve shot hundreds of rounds of the Tac-22 and it has performed well for cross-training and tactical rimfire games. We like this Norma rimfire ammo much better than the Remington and Federal bulk packs — and the price is very competitive. Right now MidwayUSA is offering 500-round boxes of Tac 22 for $59.95 (that’s just 12 cents a round).

6. Sportsman’s Guide — Henry AR-7 Packable Survival Rifle

MidwayUSA Norma .22 LR rimfire ammo Tac 22 Match 22

Here’s a unique item to add to your collection. The Henry AR-7 Survival rifle breaks down and stows in its own buttstock. Weighing just 3.5 pounds, this little semi-auto rimfire can perform pest-control duties for a farmer or rancher, or serve as a utility rifle carried in a truck or ATV. The cleverly-designed AR-7 is affordably priced at $227.99 ($216.59 for Sportsman’s Guide Club Members).

7. Amazon — Signature Zee Rings (with Pos-Align Inserts)

Amazon.com Burris Signature Zee Rings

Burris Signature Zees are our “go-to” rings for use with benchrest rifles. Right now Amazon has the 1″-diameter High Sig Zee rings on sale for $34.00 (Matte Black) or $38.00 (Nickel). Burris also offers medium height 1″-diameter Sig Zees. The 30mm Signature Zee rings are somewhat more expensive (about $50.00), but still well worth the price in our view. This Editor uses 30mm Signature Zee Rings for his personal 6mmBR rifle. The polymer inserts allow you to pre-load elevation, and also eliminate the need to lap your rings.

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January 18th, 2016

The Effect of Barrel Twist Rates on Muzzle Velocities

Barrel Twist Rate Test Bryan Litz

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
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. 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 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.

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 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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