Effects Of Cartridge Over All Length (COAL) And Cartridge Base To Ogive (CBTO) – Part 2 by Bryan Litz forBerger Bullets. Part One of this series focused on the importance of COAL in terms of SAAMI standards, magazine lengths, seating depths, and pressure levels. Another measure of length for loaded ammunition is highly important to precision, namely Cartridge Base to Bullet Ogive Length (CBTO).
Figure 2. Chamber throat geometry showing the bullet jump to the rifling or lands.
Look at Figure 2. Suppose the bullet was seated out of the case to the point where the base of the bullet’s nose (ogive) just contacted the beginning of the riflings (the lands) when the bolt was closed. This bullet seating configuration is referred to as touching the lands, or touching the riflings and is a very important measurement to understand for precision hand-loading. Due to the complex dynamics of internal ballistics which happen in the blink of an eye, the distance a bullet moves out of the case before it engages the riflings is highly critical to precision potential. Therefore, in order to systematically optimize the precision of his handloads, it’s critically important that the precision hand-loader understands how to alter bullet seating depth in relation to the barrel rifling. Part of the required knowledge is understanding how to accurately and repeatably measure the Cartridge Base To Ogive (CBTO) dimension. This is explained in the FULL ARTICLE.
Bryan Litz offers an extended discussion on how to measure CBTO using different tools and methods, including the Hornady OAL gauge. You can read this discussion in the full article found on the Berger Bullets website. CLICK HERE to Read Full Article.
Why Not Use CBTO as a SAAMI Standard?
If CBTO is so important to rifle accuracy, you might ask, “Why is it not listed as the SAAMI spec standard in addition to COAL?” There is one primary reason why it is not listed in the standard. This is the lack of uniformity in bullet nose shapes and measuring devices used to determine CBTO.
Figure 4. Two different bullet shapes, seated to the same CBTO length, but different COAL. Note the shiny scratches on the bullets made by the comparator tool which indicates a point on the bullet ogive near where the ogive will engage the riflings.
Benefits of Having a Uniform CBTO
There is another aspect to knowing your CBTO when checking your COAL as it pertains to performance. With good bullets, tooling, and carefully-prepared cases you can easily achieve a CBTO that varies less than +/- .001″ but your COAL can vary as much as .025″ extreme spread (or more with other brands). This is not necessarily bad and it is much better than the other way around. If you have a CBTO dimension that varies but your COAL dimension is tight (within +/- .002″) then it is most likely that your bullet is bottoming out inside the seater cone on the bullet tip. This is very bad and is to be avoided. It is normal for bullets to have precisely the same nose shape and it is also normal for these same bullets to have nose lengths that can vary as much as .025″.
Summary of Cartridge Base To Ogive (CBTO) Discussion
Here are four important considerations regarding bullet seating depth as it relates to CBTO:
1. CBTO is a critical measurement to understand for handloaders because it’s directly related to precision potential, and you control it by simply setting bullet seating depth.
2. Tools and methods for measuring CBTO vary. Most of the measurement techniques have pitfalls (which may give rise to inconsistent results) that you should understand before starting out.
3. A CBTO that produces the best precision in your rifle may not produce the best precision in someone else’s rifle. Even if you have the same rifle, same bullets, same model of comparator gauges, etc. It’s possible that the gauges are not actually the same, and measurements from one don’t translate to the same dimension for another.
4. Once you find the CBTO that produces the best precision in your rifle, it’s important to allow minimal variation in that dimension when producing quality handloads. This is achieved by using quality bullets, tooling, and properly preparing case mouths and necks for consistent seating.
Here’s a feel-good story, particularly for those of us getting up in years. Walt Berger recently proved you are as young as you feel — and you can enjoy shooting success at any age. Walt Berger, well into his 80s, won a big benchrest victory last month, taking the Sporter Class 100-yard Aggregate at the 2014 NBRSA Score Nationals. In so doing, Walt earned his 20th Hall of Fame Point. That’s a great accomplishment for the Elder Statesman of Benchrest. Congrats to Walt! And, yes, of course, Walt was shooting a projectile made by Berger Bullets — the 6mm 65gr BT Target bullet.
About Walt Berger
Walt Berger started making rifle bullets in 1955 because he believed he could make better bullets than those that were available at the time. He regularly participated in benchrest shooting competitions (and still does today), which requires the highest levels of precision in all components. In 1987, Walt grew his bullet making operation beyond a part time hobby after encouragement from his second wife Eunice (Walt lost his first wife Mary to cancer). Together, they grew the business into a large-scale precision rifle bullet-making operation.
Walt was born at the end of the Golden Twenties and the beginning of the Great Depression. His story is about overcoming great odds and seeing things through to success when almost everyone around him was convinced he would fail.
Walt Berger with two younger generation Berger Bullets employees at the 2014 NRA Annual Meeting.
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Brownells is offering more than month of deals on AR-15 hardware. Brownells’s “Back In Black Rifle Event” features six weeks of special, discount pricing on AR-15 upper receiver parts kits and accessories. The event culminates with blowout specials on the official Black Rifle Friday Weekend (from Friday, November 28 through Cyber Monday, December 1st).
Each Monday, leading up to Black Rifle Friday, Brownells will unveil a new package that includes all the required parts (except for lower receiver) to build a different version of the AR-15. Every package will give customers significant savings compared to buying all the parts separately(and eliminate the chance of overlooking important items).
“Rumble on the Range”, the 3-Gun Nation (3GN) Championship, takes place today, October 25th at the U.S. Shooting Academy in Tulsa, Oklahoma. The 2014 FNH USA 3-Gun Nation Pro Series culminates in this season-ending event. This is a big money match, with serious prize money going to the winners. Top 3GN Pro Series competitors will duel in a head-to-head, no holds barred shoot-off for cash, prizes and the championship title.
There are 40 competitors — 32 men and 8 women — with separate classes for the guys and the gals. In the men’s championship, the top 32 male finalists will compete for a $50,000 cash payday sponsored by Leupold and NRA Sports. Shooters will use pistols, AR-platform rifles, and shotguns — all tricked out for maximum speed and high capacity.
The 3-Gun Nation Ladies Professional Series, sponsored by Samson Manufacturing, concludes with the top eight (8) ladies competing for $25,000 Cash. The shooters to beat are 2013 Mens’ Champion SSG Daniel Horner of the USAMU and 2013 Ladies’ Champion Lena Miculek (at right).
Watch Video from 2013 3-Gun Nation Championship
HOW IT WORKS:
The event will feature 3 stages of fire (shoot-off stages). Each of the top 32 (males) and 8 (females) will be paired against each other based on series rank. The first of the paired competitors to complete the course of fire will advance. Stage 1 will feature 32 males; 8 females. Stage 2 will feature 16 males; 4 females. Stage 3 will feature the final 8 males; final 2 females. The final male will win the $50,000 cash prize. The final female will win the $25,000 cash prize.
U.S. Shooting Academy
6500 East 66th St N
Tulsa, OK 74117
Saturday, October 25
All Day 8:00 AM-6:00 PM
Grand Finale: 4:00-6:00 PM
3-Gun Nation Side Stage
A special Side Stage will be open to the public with guns and ammo provided. Spectators can try their hands at 3-Gun, shooting pistols, AR-type carbines, and shotguns. The top score wins a DPMS AP4 Carbine!
Machine Gun Shoot
A machine gun demo featuring a wide variety of full-auto firearms with be open to the public, under the direction of the U.S. Shooting Academy Range staff. Ammo fees apply.
Sneaky Ladies. Maggie Reese (left) and Janna Reeves (right) try to steal the big $25,000 check!
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Looking for a shooting range near you? There’s a new mobile App for that. The National Shooting Sports Foundation (NSSF) has released an all-new Where To Shoot mobile App that locates shooting ranges. This App is offered for Android devices as well as Apple iPhones and iPads.
Available for free in the Apple App Store and Google’s Android App Store, Where To Shoot puts North America’s most comprehensive directory of shooting ranges in the palm of your hand. It also includes video tips for shooters, news and firearm-safety information.
Users can search by current location or zip code and find specifics about each range, including shooting activities offered, accessibility and contact information. The app also makes it easy to get directions to the range.
The app is modeled after NSSF’s popular WhereToShoot.org® website and is updated frequently with range information in every U.S. state and Canadian province. New tips for hunters and shooters are also added regularly.
In recent years, the ranks of first-time handgun buyers have grown dramatically. Thousands upon thousands of Americans are purchasing their first-ever pistol. With so many handgun options available these days (from derringers to Desert Eagles) many first-time buyers have trouble making a choice.
A close relative recently contacted this Editor. Wanting to get started in handgunning, he sought my advice on purchasing his first handgun. “Should I get a Glock?”, he asked. “No” was my response. “Well how about an M&P?” he inquired. “Better ergos” I said, “but ‘No’ is still my reply.” “OK, how about a KelTec, they’re cheap…” “Absolutely not”, I replied.
I could tell he was getting annoyed, when he said “OK, Mr. know-it-all, so what handgun should I get?” Calmly, I replied: “Get a .22-caliber rimfire revolver. You will never out-grow it. You will learn sight alignment and trigger control. You can practice with inexpensive ammunition. A good .22 revolver will be considerably more accurate than 90% of the self-loading pistols you could buy. If you get a Smith & Wesson, you will keep the gun for the rest of your life and pass it on to your kids. If you or your heirs ever wear out the barrel or cylinder, Smith & Wesson will replace the parts for free, forever.”
First Handgun Choice — A very good choice for a first handgun is a Smith & Wesson .22 LR revolver, such as the S&W model 617. The model 617 is extremely accurate, with a very crisp trigger (in single-action mode), and good sights.
You can learn all the fundamentals with this ultra-reliable handgun, shooting inexpensive .22 LR ammo. The model 617 is rugged, durable, and can give you a lifetime of shooting fun. Once you have mastered the basics of shooting with a .22 LR, you can move on to larger caliber handguns suitable for self-defense. Below is a slide-show illustrating a S&W model 617 ten-shot, with 6″ barrel. S&W also makes a 4″-barrel version of this revolver. (See: Shooting Demo Video with 4″ model 617.)
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Here’s a handy product for pistol shooters and 3-Gun competitors. The NRA Handgunner Backpack provides a convenient transport solution for your pistols, magazines, and assorted range gear. This product offers all the carrying capacity of a large range bag, in a design that, when worn on your back, leaves your hands free to haul long-gun cases, target frames, spotting scopes, or other bulky hardware. Measuring 17″ wide, 22″ high and 9″ deep, the pack has plenty of room for your gear.
Quad-Pistol Gear Hauler
The cleverly-designed Handgunner Backpack carries up to four pistols. Undo the zipper, slide out the compartment, place your pistols in one of the four foam gun cradles. Store your magazines in a zip-up side pocket with six (6) individual mag sleeves. There are also specially designed compartments for ammo boxes, muffs, protective eyewear, target stapler, and more. You’ll find handy embroidered patches showing the right spot for each gear item.
Lars Dalseide, editor of the NRAblog, tells us this pack is comfortable and sturdy. The shoulder straps and the rear back panel feature moisture-wicking padding and the pack comes with a waterproof cover. And the pack won’t collapse when you set it on a bench — it stands up on its own.
We’re impressed with the design and features of this pack. A lot of smart thinking went into its design. As you might expect though, because the Handgunner Backpack has so many features, it’s not cheap. This specialized backpack sells for $119.95 at the the NRA Online Store. We don’t think that’s too much, considering what this pack can do. This could be a sweet Xmas gift for the pistolero or 3-Gun shooter in the family. If you are running a shooting match, the Handgunner Backpack would make a great prize — way more useful than a walnut plaque.
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Got fifty bucks? Well that’ll buy you an AR Lower this week. Quite simply, this is the best AR deal we’ve seen this year, and one of the best values on a firearm receiver we can remember. Right now, while supplies last, Brownells.com is offering Bushmaster-brand AR-15 stripped lower receivers for just $49.99. You read that right — you can get a major manufacturer AR lower for under fifty bucks. That’s a savings of $120.00 off the normal price. Get them while you can.
NOTE: Stripped lowers are considered the firearm, so this must be delivered to an FFL-holder. It is fairly easy to complete the lower with readily available parts and the trigger group of your choice.
Bushmaster Stripped Lower Receiver Product Description
Receiver is a rigid 7075 T6 aluminum forging with extra metal in the right places for added strength without unnecessary bulk. Features a beefy, M16A2-pattern reinforced area around the front pivot pin, a strengthening ridge over the receiver extension threads, and a ridge around the mag release button to guard against accidental magazine drop by preventing unintentional button activation. Bead blasted after machining to ensure a uniform, non-reflective surface before application of lusterless black military hardcoat A8625, Type III, Class 2 anodized finish that adds surface strength and resists abrasion. A final, nickel acetate seal coat provides extra protection against corrosion. Stripped lower is the perfect companion for Bushmaster Lower Receiver Parts Kit, available separately
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Kirsten Joy Weiss is a phenomenal off-hand rifle shooter. In this video, Kirsten performs a classic Annie Oakley trick shot, cutting a playing card in half with a bullet. Splitting a playing card would be hard enough with a scoped rifle shot from the bench. But Kirsten makes this amazing shot from standing position, shooting over iron sights, with an inexpensive rimfire lever gun. Trust us, that’s not easy. It did take Kirsten three tries, but we’re still impressed.
To accomplish this trick shot, Kirsten’s horizontal aim had to be ultra-precise. A playing card is only 0.25mm thick (about 1/100th of an inch). That leaves almost no room for error.
GIF Animation Shows Bullet Slicing Card in Half:
We know top benchresters can put five shots in one ragged hole at 100 yards, used a scoped rifle sitting on a stable rest. But make those folks stand on their hind legs, hold the rifle, and aim over primitive iron sights, and some of those benchrest aces would be lucky to hit a dinner plate at 100 yards. Kudos to Kirsten for making this great shot.
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For many years, the Varmint Hunters Association (VHA) has produced an excellent print periodical, The Varmint Hunter Magazine. Along with hunting stories, the magazine features articles about precision reloading and methods for accurizing rifles. The Varmint Hunter Magazine is available by subscription, and you can also purchase back issues through the VHA Online Store.
Right now the VHA is offering two FREE digital editions of The Varmint Hunter Magazine. Can’t beat that price. Click the links below to view (or download) the latest Fall 2014 Edition (Issue #92) or the previous Summer 2014 Edition (Issue #91). These digital eZines can be read on your computer or by most mobile devices. But since these are complete magazines, it make take a minute or two to download the full PDF files (be patient).
Sooner or later you’ll want to clean your rifle brass, even if you aren’t fussy about appearance. You can tumble your cases in a vibratory tumbler with dry media, but that can leave cases with a fine layer of dust, or worse yet, clogged flash holes. As an alternative to tumbling, many shooters are experimenting with ultrasonic case cleaning. Here are three tips to achieve the best results when using ultra-sound to clean your brass:
Try a Commercial Ultrasonic Cleaning Solution
As a companion product to its new ultrasonic cleaning tank, Hornady is selling a citric-acid based One Shot™ Sonic Clean™ Solution, that is claimed to speed up cleaning times, and not leave your brass an odd pinkish color like some “home-brew” solutions. We’ve heard good reports about the One-Shot Solution (cartridge case formula) as well as Citranox®. Both products are economical to use since you dilute them heavily with water. For example, Hornady recommends you mix forty (40) parts water to one part of One Shot Sonic Clean.
Forum member Dave B is a chemist/physicist with decades of experience working with the ultrasound process. Dave tried a variety of solutions and he favors a mix of water and Citranox®. Dave notes: “So far I’ve been very impressed with the Citranox. Once- or twice-fired brass clean up very quickly. The worst cases I tried were 6 Dashers that had been fired ten times with Varget and never cleaned. The worst fouling was in the bottom of the case around the flash hole. They took longer and I used a more concentrated cleaning solution but they did come out clean. The price is reasonable. I paid $35 a gallon and for once- or twice-fired cases I dilute the cleaner 100 to 1. There is much less chemical reaction with the brass than there is with vinegar. No weird colors, just shiny bright. I even used it with hot water, which speeds up the cleaning process. The cleaner is mostly detergents with a little citric acid. Even at a 1:75 ratio my $35 worth of cleaner will make 75 gallons of solution.” The price has gone up a bit since Dave acquired his Citranox, but Amazon.com sells Citranox for $45.50 per gallon.
Another good ultrasonic solution is L&R non-ammoniated Safety Cleaning Solution, sold by Brownells, item #515-000-004. Brownell’s L&R solution is non-toxic and biodegradeable. The strong surfactant in L&R solution helps penetrate the grit so the ultrasonic cavitation can carry the grime away.
De-Gas the Solvent Before Adding Brass
One of our readers, Eddy M. in Glasgow, Scotland writes: “I have read a couple of articles recently about ultrasonic cleaning of cases and not one has mentioned de-gassing the cleaning liquid before starting to clean items. As an engineer who traveled around for ten years servicing ultrasonic tanks I would like to point out that the cleaning liquid when first put into the tank has invisible dissolved air bubbles in it which will absorb ultrasonic energy until the liquid de-gasses. (Ten minutes in a powerful industrial tank — longer in a small hobby tank). You must let the tank run on its own for 20 minutes on the first use of the liquid to allow this to happen. Only after the new liquid or re-introduced liquid has been de-gassed will the tank give good results.”
Apply Dry-Lube Inside Case Necks
Jason Baney has found that Ultrasonic cleaning leaves the inside of the case-necks so “squeaky clean” that there is excess friction when seating bullets. On a fired case that has been cleaned conventionally (no ultra-sound), a thin layer of carbon remains to lubricate the bullet entry and exit. To restore that lubricity in cases cleaned with ultrasound, Jason applies a dry lube to the inside of his case necks. Jason prefers the $10.95 moly dry lube kit from Neconos.com. With this kit, small carbon steel balls transfer moly to the neck when you place your brass nose-down in the container.
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