What is “Overbore”? That’s a question rifle shooters can debate to no end. This article from our archives proposes one way to identify “overbore cartridges”. We think the approach outlined here is quite useful, but we know that there are other ways to define cartridges with “overbore” properties. Whenever we run this article, it stimulates a healthy debate among our readers — and that is probably a good thing.
Forum Member John L. has been intrigued by the question of “overbore” cartridges. People generally agree that overbore designs can be “barrel burners”, but is there a way to predict barrel life based on how radically a case is “overbore”? John notes that there is no generally accepted definition of “overbore”. Based on analyses of a wide variety of cartridges, John hoped to create a comparative index to determine whether a cartridge is more or less “overbore”. This, in turn, might help us predict barrel life and maybe even predict the cartridge’s accuracy potential.
John tells us: “I have read countless discussions about overbore cartridges for years. There seemed to be some widely accepted, general rules of thumb as to what makes a case ‘overbore’. In the simplest terms, a very big case pushing a relatively small diameter bullet is acknowledged as the classic overbore design. But it’s not just large powder capacity that creates an overbore situation — it is the relationship between powder capacity and barrel bore diameter. Looking at those two factors, we can express the ‘Overbore Index’ as a mathematical formula — the case capacity in grains of water divided by the area (in square inches) of the bore cross-section. This gives us an Index which lets us compare various cartridge designs.”
OVERBORE INDEX Chart
So what do these numbers mean? John says: “My own conclusion from much reading and analysis is that cartridges with case volume to bore area ratio less than 900 are most likely easy on barrels and those greater than 1000 are hard on barrels.” John acknowledges, however, that these numbers are just for comparison purposes. One can’t simply use the Index number, by itself, to predict barrel life. For example, one cannot conclude that a 600 Index number cartridge will necessarily give twice the barrel life of a 1200 Index cartridge. However, John says, a lower index number “seems to be a good predictor of barrel life”.
John’s system, while not perfect, does give us a benchmark to compare various cartridge designs. If, for example, you’re trying to decide between a 6.5-284 and a 260 Remington, it makes sense to compare the “Overbore Index” number for both cartridges. Then, of course, you have to consider other factors such as powder type, pressure, velocity, bullet weight, and barrel hardness.
Overbore Cases and Accuracy
Barrel life may not be the only thing predicted by the ratio of powder capacity to bore cross-section area. John thinks that if we look at our most accurate cartridges, such as the 6 PPC, and 30 BR, there’s some indication that lower Index numbers are associated with greater inherent accuracy. This is only a theory. John notes: “While I do not have the facilities to validate the hypothesis that the case capacity to bore area ratio is a good predictor of accuracy — along with other well-known factors — it seems to be one important factor.”
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Nosler has introduced a new 6.5mm (.264 caliber) hunting cartridge, the 26 Nosler. Nosler will initially offer 26 Nosler cartridge brass, and then, eventually, 26 Nosler loaded ammunition.
This new cartridge is designed to be a speedy, flat-shooting hunting cartridge, with performance exceeding a 6.5-284. This is possible because the 26 Nosler is a big, long cartridge with plenty of “boiler room”. Length from base to neck/shoulder junction is 2.33″ for the 26 Nosler, compared to 1.91″ for the 6.5-284 (and 2.04″ for a 7mm Rem Magnum). The 26 Nosler has a 35° shoulder angle and a magnum-size 0.534″ outside rim diameter.
The 26 Nosler cartridge can drive the Nosler 129 grain, AccuBond® LR bullet at 3400 fps. Zeroed at 350 yards, the 26 Nosler has a Point Blank Range of 0-415 yards. Loaded with the 129gr Accubond, the 26 Nosler retains as much velocity at 400 yards as a .260 Rem produces at the muzzle. This makes the 26 Nosler a “quintessential deer, antelope and long-range” cartridge according to company CEO/President Bob Nosler.
Bryce Towsley has authored an informative article on Reclaiming .223 Rem Brass. Writing for Shooting Illustrated Online, Towsley confesses: “I’m a brass horder…. I end every shooting match on my hands and knees. If the rest of the competitors want to litter the range with their discarded cases, I see it as my civic duty to clean up the mess.” If you burn through a lot of .223 Rem ammo on the varmint fields or in multi-gun matches, we suggest you read Towsley’s article.
Towsley advises that you need to be cautious with range pick-up brass: “Range brass is full of dirt, dust, sand and debris that can be damaging to loading dies, as well as causing other problems.” So, range pick-up brass must be cleaned and then sorted carefully. Towsley explains that you should toss brass that is badly dented, and you have to make sure to remove the primer pocket crimp in military brass. This can be done with a crimp reamer or a swaging tool such as the Dillon Super Swage 600. The latter works well, but Towsley cautions: “For the swager to work properly, you must sort the cases by brand and lot, and then readjust the swager for each new lot.”
Trimming Quantities of Brass
Before loading, “reclaimed” range brass should, of course, be full-length sized and you should trim all the brass to the same length. “Cases that are too long can cause all kinds of problems”, explains Towsley.
We envy the system Towsley uses to trim brass. He has a Dillon Rapid Trim 1200B set up on the top of a single-stage press: “You simply insert a case into the shell holder and raise the ram to trim it instantly. The process is so fast, it almost feels like cheating.” The Rapid Trim is a very neat gadget — it even has an attachment for a vacuum hose to remove the cuttings. The photo at right shows a 1200B installed on a Dillon progressive press.
We definitely recommend you read Bryce Towsley’s Reclaiming Range Brass Article from start to finish. The article offers useful advice that will help you reload any rifle cartridge — not just .223 Rem range brass. Towsley also showcases many good labor-saving devices that can speed up and simplify the process of bulk rifle cartridge reloading.
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Norma is making a big push to expand its presence in the North American market. As part of this effort, Norma is introducing seven (7) new types of cartridge brass for 2014. We’re pleased to report that Norma-USA will be importing top-quality brass for the 6.5 Grendel, and 6.5 Creedmoor, two popular target cartridges. In addition, for 2014, Norma will offer 7mm RUM, 7mm Blaser Magnum, 300 AAC Blackout (300 BLK), .300 RUM, and the .338 Blaser Mag. The Norma brass we have shot in other chamberings (6 PPC, 6mmBR Norma, 6XC, .243, 7mm RSAUM) has all been excellent, giving good accuracy. Case weights were very consistent and the neck-wall thickness was very uniform, particularly with the PPC and BR brass. The new 300 BLK brass is an important offering for AR shooters. (NOTE: You can also make 300 BLK cases from Norma or Lapua .221 Fireball brass).
Though the annealing “shadow” may not be as visible as with Lapua brass, the case necks of Norma brass cartridges are indeed annealed near the end of the manufacturing process. This assures more consistent neck tension — something critical to accuracy. Most of the new cartridge brass offerings should be be available at vendors by early April, 2014. You can get Norma brass from Bullets.com, Grafs.com and Midsouth Shooters Supply, as well as many other online vendors.
New Norma-USA Brass Offerings for 2014:
7mm Blaser Magnum
300 AAC Blackout (300 BLK)
.338 Blaser Magnum
Product Tip from EdLongrange. We welcome reader submissions.
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On his Riflemans’ Journal blog, German Salazar wrote an excellent article about cartridge Case-Head Separation. We strongly recommend that you read this article. German examines the causes of this serious problem and he explains the ways you can inspect your brass to minimize the risk of a case-head separation. As cases get fired multiple times and then resized during reloading, the cases can stretch. Typically, there is a point in the lower section of the case where the case-walls thin out. This is your “danger zone” and you need to watch for tell-tale signs of weakening.
The photo below shows a case sectioned so that you can see where the case wall becomes thinner near the web. German scribed a little arrow into the soot inside the case pointing to the thinned area. This case hadn’t split yet, but it most likely would do so after one or two more firings.
One great tip offered by German Salazar involves using a bent paper clip to detect potential case wall problems. Slide the paper clip inside your case to check for thin spots. German explains: “This simple little tool (bent paper clip) will let you check the inside of cases before you reload them. The thin spot will be immediately apparent as you run the clip up the inside of the case. If you’re seeing a shiny line on the outside and the clip is really hitting a thin spot inside, it’s time to retire the case. If you do this every time you reload, on at least 15% of your cases, you’ll develop a good feel for what the thin spot feels like and how it gets worse as the case is reloaded more times. And if you’re loading the night before a match and feel pressured for time — don’t skip this step!”
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California shooter Mark LaFevers has come up with a slick, adjustable fixture that delivers a precise, repeatable inside-neck chamfer every time. He uses a Holland Case Mouth Chamfer Tool with a 14° cutter, but this set-up works equally well with other chamferers with an extended handle. With Mark’s tool jig, the Holland Tool inserts through the top, indexing vertically off a shoulder. A small recess is cut in the center of the wood base for the case head. The tool mount can be raised or lowered with the adjusting bolts on all four corners. Simply slide a trimmed-to-length case in the middle, give the Holland Tool a few spins, and you get a perfect, identical chamfer every time. Now that’s ingenuity! Mark isn’t planning to produce these commercially, but he’s happy if someone wants to copy his jig design.
NOTE: In the photos above, you see an older version of the tool. Hollands has improved the design of its current 14° Chamfer Tool. The cutting head now has a 3-flute design that provides a smoother, chatterless cut. The head is now made of carbide so it cuts faster and holds its cutting edge longer. This tool is available from Holland’s Shooters Supplies for $32.00 (item CMCT-CAR).
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Lapua just dropped a bombshell — multiple bombshells, in fact. Lapua just announced that it will be producing .221 Fireball brass and .50 BMG brass starting early 2014. This will be the first truly match-grade brass ever offered for the .221 Fireball. That’s great news for varminters, who can use Lapua’s new .221 Fireball brass “as is” or neck it down to .20 Vartarg or 17 Fireball. Tactical shooters can also use the .221 Fireball brass to make the .300 Whisper and 300 Blackout sub-sonic cartridges. At the other end of the spectrum, ultra-long-range shooters now have a new ultra-premium brass source for the mighty .50 BMG. This is potentially a “game-changer” for fifty-cal shooters who have had to “make do” with military surplus brass for the most part. Lapua says the new brass, both .50 BMG and .221 Fireball, should be in the USA by early April, 2014. Sorry, no pricing info is yet available.
Here is the Lapua Product Announcement for .221 Fireball and .50 BMG Brass:
New 180-Grain and 150-Grain 7mm Scenar-L Bullets
The other big news from Lapua is the release of two new 7mm (.284 caliber) Scenar-L target bullets. Recognizing the popularity of 7mm cartridges among F-Class Open Division shooters, Lapua will offer a high-BC, 180-grain bullet. As part of the “L” series, this new 180-grainer bullet should exhibit extreme consistency in base-to-ogive measurements and bullet weight. We expect this new 180gr projectile to be extremely accurate in the .284 Winchester, .284 Shehane, 7mm WSM, and 7mm RSAUM — popular chamberings for F-Class and long-range benchrest shooters. No BC information has been released yet, but we expect the BC number to be quite high, giving this bullet great wind-bucking capability. In addition to the new 180gr 7mm Scenar-L, Lapua will offer a new 150gr 7mm bullet. This is optimized for medium range competition in Silhouette and Across-the-Course competition. It should offer great accuracy, but with less felt recoil than its 180-grain bigger brother.
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Chances are that many of you have packed away your ammo and shooting supplies for the winter. Maybe you put your brass in a storage bin that might also contain solvents, old rags, or used bore swabs. Well, if you use any ammonia-based solvents, we suggest you separate the brass and ammo and keep it away from potential ammonia vapors. This is because long-term exposure to ammonia fumes can cause cracks to form in your brass. This can lead to case ruptures and possible injury.
This case-cracking phenomenon has been called Season Cracking, a form of stress-corrosion cracking of brass cartridge cases. Season cracking is characterized by deep brittle cracks which penetrate into affected components. If the cracks reach a critical size, the component can suddenly fracture, sometimes with disastrous results. If the concentration of ammonia is very high, then corrosion is much more severe, and damage over all exposed surfaces occurs. The brass cracking is caused by a reaction between ammonia and copper that forms the cuprammonium ion, Cu(NH3)4, a chemical complex which is water-soluble. The problem of cracking can also occur in copper and copper alloys such as bronze.
Season Cracking was originally observed by the British forces in India a century ago. During the monsoon season, military activity was reduced, and ammunition was stored in stables until the dry weather returned. Many brass cartridges were subsequently found to be cracked, especially where the case was crimped to the bullet. In 1921, in the Journal of the Institute of Metals, the phenomenon was explained by Moor, Beckinsale, and Mallinson. Apparently ammonia from horse urine, combined with the residual stress in the cold-drawn metal of the cartridges, was responsible for the cracking.
Don’t store ammunition (or brass) for long periods in a box or container holding ammoniated solvents:
The Australia Department of Defense (AUSDOD) has also explored the problem of brass cracking caused, at least in part, by exposure to ammonia. A study was done to see whether the amount of cracking (from ammonia exposure) varied according to the duration and temperature of the annealing process used on the brass. CLICK HERE to read AUSDOD Research Report.
Story idea from Boyd Allen. We welcome reader submissions.
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When neck-turning cases, it’s a good idea to extend the cut slightly below the neck-shoulder junction. This helps keep neck tension more uniform after repeated firings, by preventing a build-up of brass where the neck meets the shoulder. One of our Forum members, Craig from Ireland, a self-declared “neck-turning novice”, was having some problems turning brass for his 20 Tactical cases. He was correctly attempting to continue the cut slightly past the neck-shoulder junction, but he was concerned that brass was being removed too far down the shoulder.
Craig writes: “Everywhere I have read about neck turning, [it says] you need to cut slightly into the neck/shoulder junction to stop doughnutting. I completely understand this but I cant seem to get my neck-turning tool set-up to just touch the neck/shoulder junction. It either just doesn’t touch [the shoulder] or cuts nearly the whole shoulder and that just looks very messy. No matter how I adjust the mandrel to set how far down the neck it cuts, it either doesn’t touch it or it cuts far too much. I think it may relate to the bevel on the cutter in my neck-turning tool…”
Looking at Craig’s pictures, we’d agree that he didn’t need to cut so far down into the shoulder. There is a simple solution for this situation. Craig is using a neck-turning tool with a rather shallow cutter bevel angle. This 20-degree angle is set up as “universal geometry” that will work with any shoulder angle. Unfortunately, as you work the cutter down the neck, a shallow angled-cutter tip such as this will remove brass fairly far down. You only want to extend the cut about 1/32 of an inch past the neck-shoulder junction. This is enough to eliminate brass build-up at the base of the neck that can cause doughnuts to form.
The answer here is simply to use a cutter tip with a wider angle — 30 to 40 degrees. The cutter for the K&M neck-turning tool (above) has a shorter bevel that better matches a 30° shoulder. There is also a 40° tip available. PMA Tool and 21st Century Shooting also offer carbide cutters with a variety of bevel angles to match your case shoulder angle*. WalkerTexasRanger reports: “I went to a 40-degree cutter head just to address this same issue, and I have been much happier with the results. The 40-degree heads are available from Sinclair Int’l for $13 or so.” Forum Member CBonner concurs: “I had the same problem with my 7WSM… The 40-degree cutter was the answer.” Below is Sinclair’s 40° cutter for its NT-1000, NT-1500, and NT-4000 neck-turning tools. Item NT-3140, it sells for $12.95. There is also a 40° cutter for the NT-3000 tool, item NT-3340 ($13.95).
Al Nyhus has another clever solution: “The best way I’ve found to get around this problem is to get an extra shell holder and face it off .020-.025 and then run the cases into the sizing die. This will push the shoulder back .020-.025. Then you neck turn down to the ‘new’ neck/shoulder junction and simply stop there. Fireforming the cases by seating the bullets hard into the lands will blow the shoulder forward and the extra neck length you turned by having the shoulder set back will now be blended perfectly into the shoulder. The results are a case that perfectly fits the chamber and zero donuts.”
Get an inside look at the how ammunition is made with this step-by-step production guide from Hornady. The video begins by showing the stages in production of a lead-core jacketed bullet with exposed tip, such as the Hornady Interlock. Next, at the 1:38″ time-mark, the video shows how cartridge cases are made, starting with small brass cups (photo right). The brass is lengthened in a series of stages involving annealing, drawing, polishing, and the formation of the case head with primer pocket. Finally, at the 2:40″ time mark, the video shows how bullets and powder are seated into cartridge cases on the Hornady assembly line. In the final production stages, the completed ammunition is tested and packaged.
Watch Ammo Production Video
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Hornady plans to start producing .50 BMG ‘Match Grade’ Cartridge Brass. MSRP is $131.99 for twenty (20) cases (Item #8772). Hornady claims the new brass will have very uniform case wall thickness, and very consistent case weight and internal capacity. Hornady has not stated when its .50 BMG brass will start shipping. When the Hornady .50 BMG brass (Item #8772) does hit the market, we expect it will be in high demand. Our friends at the Fifty Caliber Shooters Association (FCSA) tell us that it is “getting harder and harder to get your hands on good .50 Cal brass these days.”
Reloaders Rejoice! There’s a new source for bullets, brass, powder, and primers, as well as loaded ammunition. The all-new Bullets.com website offers all these products, plus reloading tools and dies, barrels, gun stocks, scopes, rings, shooting rests, range bags and much more. Primers, you need primers you say? Yes, Bullets.com currently has some types of CCI, Federal, and Remington primers in stock, including the hard-to-find CCI 450 small rifle magnum primers.
You definitely want to include Bullets.com among the vendors you visit when you need components and gun hardware. The new Bullets.com webstore will carry 8,000+ shooting-related products from over 50 top brands such as Lapua, Norma, Federal, CCI, Berger, Sierra, Berry’s, Bald Eagle, Bushnell, Hodgdon, Alliant, Nightforce, Kowa, Vortex, Winchester, MTM, Magpul and many more! Check out the website at www.bullets.com or call 1-800-235-0272 to get a free 60-page color catalog.
POWDERS IN STOCK — Among the popular powders in stock at Bullets.com today are:
Bullets.com carries projectiles from the leading bullet-makers including Berger, Lapua, Sierra, Speer, and Berrys. Yes Bullets.com has premium bullets in stock right now, including the hard-to-find Berger 6mm 105gr Hybrid, and 7mm 180gr Hybrid. Grab ‘em while you can boys!
Along with reloading components, factory ammo, and reloading dies, you’ll find the hardware you need to build a complete rifle. Bullets.com caries Bartlein barrels (in a wide range of calibers and contours), laminated gun stocks, and a full line of optics, including Nightforce, Kowa, and Vortex rifle-scopes and spotting scopes.
Who Are Those Guys? About Bullets.Com
Bullets.com was launched as a result of the intense passion for shooting by its President, Shiraz Balolia. Shiraz has been shooting pistols, rifles and shotguns for almost 40 years and has been involved in long range rifle shooting at the National and International level for almost 10 years. He served as the Captain of the U.S. F-Class Open Rifle Team for the 2013 World Championship and was a member of the 4-man team that won the 2013 Nat’l 1,000-yard Championship. He has won numerous gold medals in long range shooting and has set several National records.
Bullets.com is a division of Grizzly Industrial that was started by Mr. Balolia in 1983. During those 30 years, Grizzly became a powerhouse in the metalworking and woodworking machinery industry serving over a million regular customers and growing its warehouses with 1.2 million square feet of space in three states (WA, PA, MO).
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