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February 8th, 2016
We are often asked, “Can you recommend a good reloading book that picks up where the typical reloading manual leaves off — something that goes into more detail about the processes involved.” There is such a book, and it’s fairly recent: Metallic Cartridge Handloading: Pursuit of the Perfect Cartridge, by M.L. (“Mic”) McPherson. Released in 2013, this 425-page book goes into greater depth than McPherson’s popular intro reloading guide, Metallic Cartridge Reloading. McPherson’s latest reloading treatise covers all aspects of the reloading process: the cartridge case; maintaining, improving and loading the case; the seating and reading of primers; the loading of propellant; bullets and the loading of bullets; accurate load development; internal and external ballistics; bullet making and casting; and reloading presses.
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With hundreds of photos and illustrations, this book is a good reference for shooters getting started in precision reloading for accuracy. Compared to some other books on reloading procedures, McPherson’s new resource is more up-to-date, so it references more modern reloading tools and techniques. NOTE: This is NOT a reloading manual containing specific load data. Rather, it is a how-to book that covers the process of cartridge reloading from start to finish.
Reviews by actual book buyers:
A great resource for handloaders although a little technical for beginners. I have been reloading for 40+ years and picked up some good ideas. — Loren R.
This is a book intended for people who have been reloading for a while. The book contains very detailed information about reloading. — Kaj H.
About the Author, M.L. (“Mic”) McPherson:
Mic McPherson, Technical Editor of Hand Loader’s Digest, is the author of numerous firearms resource books including Metallic Cartridge Reloading and Accurizing the Factory Rifle. He has written scores of articles for leading gun periodicals including Precision Shooting, The Accurate Rifle, Rifle Shooter, and Varmint Hunter Magazine. Mic also served as an Editor of the 8th and 9th Editions of Cartridges of the World.
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January 11th, 2016
Here’s an item of interest to hunters (and maybe a few F-Open shooters). Nosler has just introduced a new magnum-type cartridge, the 30 Nosler. Sharing the same parent case as the 26 and 28 Nosler® cartridges, the 30 Nosler® has the case capacity to launch big 30-caliber bullets at impressive velocities (3000 FPS for a 210-grainer). Nosler says the 30 Nosler combines the best qualities of other 30-cal magnums: “The 30 Nosler® easily meets the velocity of the 300 Weatherby, headspaces on the shoulder like a 300 RUM, has an efficient powder column like the 300 WSM and fits in the same standard length action of a 300 Winchester Magnum.”
30 Nosler Will Function in a Standard Length Action
The 30 Nosler has a C.O.A.L. of 3.340″ allowing this cartridge to be operated in a standard length action for lighter weight and shorter bolt throw when compared to magnum-length actions.
The 30 Nosler is a SAAMI-standardized cartridge so there will be standardized dimensions for brass, dies, and chamber reamers. Nosler will support this new cartridge with Nosler Brass, Trophy Grade™ Ammunition and a series of M48 hunting rifles. The initial offerings in Nosler’s Trophy Grade™ Ammunition will be:
Nosler® Trophy Grade™ Ammunition: 180gr AccuBond® 3200 fps
Nosler® Trophy Grade™ LR Ammunition: 210gr AccuBond® LR 3000 fps
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November 25th, 2015
Here’s something you don’t see very often — Lapua cartridge brass on sale. As part of its Back-to-Black promotion, Brownells has deeply discounted its inventories of Lapua Brass. For most cartridges/calibers, the price has been reduced at least $10.00 per 100-count box. Here are the sale prices, good through the end of the week:
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.222 Rem – $53.99 (reg. $61.99)
.223 Rem – $53.99 (reg. $61.99)
220 Russian – $89.99 (reg. $99.99)
.22-250 – $89.99 (reg. $99.99)
6mmBR – $81.99 (reg. $91.99)
.243 Winchester – $89.99 (reg. $99.99)
6.5 Grendel – $89.99 (reg. $99.99)
6.5×47 Lapua – $99.99 (reg. $109.99) |
260 Remington – $89.99 (reg. $99.99)
6.5×55 Swedish – $71.99 (reg. $81.99)
6.5-284 – $109.99 (reg. $124.99)
7.62×39 – $54.99 (reg. $59.99)
.308 Winchester – $69.99 (reg. $79.99)
.308 Win Palma – $76.99 (reg. $86.99)
.30-06 Springfield – $99.99 (reg. $109.99)
.338 Lapua Magnum – $239.99 (reg. $269.99) |
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October 23rd, 2015
Efficient cartridges make excellent use of their available powder and case/bore capacity. They yield good ballistic performance with relatively little recoil and throat erosion.
Cartridge Efficiency: A Primer (pun intended!) by USAMU Staff
Each week, the U.S. Army Marksmanship Unit (USAMU) publishes a reloading article on its Facebook Page. In this week’s article, the USAMU discusses cartridge case efficiency and its benefits. While this is oriented primarily toward NRA High Power Rifle and Long Range (1000-yard) competition, these factors also apply to medium/big game hunters. Assuming one’s rifle and ammunition are accurate, key considerations include ballistic performance (i.e., resistance to wind effects, plus trajectory), recoil, and throat erosion/barrel life.
Efficient cartridges make excellent use of their available powder and case/bore capacity. They yield good ballistic performance with relatively little recoil and throat erosion. A classic example in the author’s experience involved a featherweight 7x57mm hunting/silhouette rifle. When loaded to modern-rifle pressures, just 43-44 grains of powder pushed a 139gr bullet at 2900 fps from its 22” barrel. Recoil in this light rifle was mild; it was very easy to shoot well, and its performance was superb.
An acquaintance chose a “do everything” 7mm Remington Magnum for use on medium game at short ranges. A larger, heavier rifle, it used ~65 grains of powder to achieve ~3200 fps with similar bullets — from its 26″ barrel. Recoil was higher, and he was sensitive to it, which hampered his shooting ability.
Similarly efficient calibers include the 6mm BR [Norma], and others. Today’s highly-efficient calibers, such as 6mm BR and a host of newer developments might use 28-30 grains of powder to launch a 105-107gr match bullet at speeds approaching the .243 Winchester. The .243 Win needs 40-45 grain charges at the same velocity.
Champion-level Long Range shooters need every ballistic edge feasible. They compete at a level where 1″ more or less drift in a wind change could make the difference between winning and losing. Shooters recognized this early on — the then-new .300 H&H Magnum quickly supplanted the .30-06 at the Wimbledon winner’s circle in the early days.
The .300 Winchester Magnum became popular, but its 190-220gr bullets had their work cut out for them once the 6.5-284 and its streamlined 140-142gr bullets arrived on the scene. The 6.5-284 gives superb accuracy and wind performance with about half the recoil of the big .30 magnums – albeit it is a known barrel-burner.
Currently, the 7mm Remington Short Action Ultra-Magnum (aka 7mm RSAUM), is giving stellar accuracy with cutting-edge, ~180 grain bullets, powder charges in the mid-50 grain range and velocities about 2800+ fps in long barrels. Beyond pure efficiency, the RSAUM’s modern, “short and fat” design helps ensure fine accuracy relative to older, longer cartridge designs of similar performance.
Recent design advances are yielding bullets with here-to-fore unheard-of ballistic efficiency; depending on the cartridge, they can make or break ones decision. Ballistic coefficients (“BC” — a numerical expression of a bullet’s ballistic efficiency) are soaring to new heights, and there are many exciting new avenues to explore.
The ideal choice [involves a careful] balancing act between bullet BCs, case capacity, velocity, barrel life, and recoil. But, as with new-car decisions, choosing can be half the fun!
Factors to Consider When Evaluating Cartridges
For competitive shooters… pristine accuracy and ballistic performance in the wind are critical. Flat trajectory benefits the hunter who may shoot at long, unknown distances (nowadays, range-finders help). However, this is of much less importance to competitors firing at known distances.
Recoil is an issue, particularly when one fires long strings during competition, and/or multiple strings in a day. Its effects are cumulative; cartridges with medium/heavy recoil can lead to shooter fatigue, disturbance of the shooting position and lower scores.
For hunters, who may only fire a few shots a year, recoil that does not induce flinching during sight-in, practice and hunting is a deciding factor. Depending on their game and ranges, etc., they may accept more recoil than the high-volume High Power or Long Range competitor.
Likewise, throat erosion/barrel life is important to competitive shooters, who fire thousands of rounds in practice and matches, vs. the medium/big game hunter. A cartridge that performs well ballistically with great accuracy, has long barrel life and low recoil is the competitive shooter’s ideal. For the hunter, other factors may weigh more heavily.
Cartridge Efficiency and Energy — Another Perspective
Lapua staffer Kevin Thomas explains that efficiency can be evaluated in terms of energy:
“Cartridge efficiency is pretty straight forward — energy in vs. energy out. Most modern single-based propellants run around 178-215 ft/lbs of energy per grain. These figures give the energy potential that you’re loading into the rifle. The resulting kinetic energy transferred to the bullet will give you the efficiency of the round. Most cases operate at around 20-25% efficiency. This is just another way to evaluate the potential of a given cartridge. There’s a big difference between this and simply looking at max velocities produced by various cartridges.”
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September 8th, 2015
“Once-fired, lot-number-traceable Lake City 7.62×51. This has been de-primed, pocket-swaged, small base body die’d, full-length sized, trimmed with a Gracey Trimmer, and tumbled. Now it’s shiny again. It’s like gourmet macaroni for shooters!” — Dennis Santiago
Our friend Dennis Santiago shoots a variety of disciplines, including Vintage Military Rifle. He burns through a lot of brass, some of it run through gas guns, so he often saves money by acquiring once-fired Lake City Arsenal brass. But that stuff is often pretty ugly when it arrives. For his “previously-owned” Lake City Brass, Dennis does a complete case prep operation and a thorough cleaning/tumbling operation. Special attention is paid to the primer pockets — they are swaged to remove the military crimp. The cases are trimmed and chamfered in one operation using a Gracey Powered Case Trimmer.
Dennis likes once-fired Lake City brass for some applications. The price is right, and with proper attention to detail during case prep, Lake City brass can shoot exceptionally well indeed. You may want to sort Lake City brass by weight. To remove the military crimp you have a variety of options — you can swage it out with a special tool like Dennis does, or you can ream out the crimp. For Wilson trimmer owners, Wilson makes a special Primer Pocket Reamer to remove military crimps. It works very well, as shown below:
 
Case Processing with the Gracey Trimmer
Designed by Doyle Gracey 30 years ago, the Gracey machine trims, deburs and chamfers in one operation, indexing off the case shoulder. The manufacturer claims the Gracey will process 20 cases per minute while holding .002″ tolerances on trim length. Two steel cutters are employed — one cutter trims the case to length and puts a chamfer on the inside of the case mouth. The second cutter removes the burr from the outside of the case-mouth. A 1/15 hp motor turns 1550 rpm. Interestingly, a clamped rubber hose serves as the “drive shaft” to turn the cutting head.
Trey Tuggle, writing in Shooting Sports USA, reviewed the Gracey Trimmer, giving it generally high marks, though it lacks some of the refinements of the more modern Giraud Trimmer:
“This model may have a piece of wood for a base, no on-off swith and a piece of bent sheet metial to contain brass shavings — but it does trim, debur and chamfer with great speed and accuracy at a nice price. The [Gracey] two-bladed cutter requires a little more patience to adjust than the one-piece cutter on the Giraud, but it gets the job done superbly. [The Gracey] does the job for less money, if you’re willing to tinker with the cutter blade adjustment.” Gracey machines are still available new from MatchPrep.com for $335.00 (or $235.00 without motor).
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April 22nd, 2015
OK, guys, it’s time to practice your downloading skills. Here’s a very handy cartridge information sheet you will definitely want to save for future reference. Shown below is Page One of the Primer Size and Bullet Diameter Chart created by Graf & Sons. This chart shows the bullet diameter and primer size for more than 320 popular cartridges*. The full three-page chart is available in PDF format for easy printing.
DOWNLOAD Graf’s Cartridge Primer Size and Bullet Diameter Chart
NOTE: If you have the PDF reader installed in your browser, the Graf’s Chart may open in a new tab when you click on the image above. To save the three-page PDF file to your computer or device, click the Floppy Disc icon that appears in the lower right (after the PDF file opens). Here is the direct link: http://www.grafs.com/uploads/technical-resource-pdf-file/12.pdf.
Note: There are a few mistakes. If you are making 22 BR from Lapua brass, you’ll want a small rifle primer. Likewise with 25-20 WCF, you want a small primer.
Resource Tip from EdLongrange. We welcome reader submissions.
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December 4th, 2014
Every year we anxiously await the new product announcement from Lapua. In 2014, Lapua brought out new bullets and new cartridge brass — .221 Fireball and .50 BMG. For 2015, Lapua once again brings out new brass offerings, this time three new flavors of cartridge brass, all made to Lapua’s exacting standards. First, Lapua will introduce factory 300 AAC Blackout (300 BLK) brass. This promises to take this highly-efficient, AR-friendly .30-caliber cartridge to another accuracy level. Second, Lapua will offer premium brass for the 7mm-08 cartridge, a very popular round among hunters and silhouette shooters. Lastly, in 2015, Lapua will produce 8x57mm JS brass. That’s good news for fans of this classic Mauser cartridge.
300 AAC Blackout Brass
Lapua’s Press release states: “Few cartridges have generated as much immediate interest as the 300 Blackout. Standardized by AAC, this diminutive cartridge is derived from the 223 Remington. Intended specifically for use in suppressed firearms, the versatility of the Blackout has appealed to a much broader range of shooters than just the audience for which it was originally designed. [Originally] intended to drive 220 grain bullets at subsonic velocities, the switch to lightweight bullets such as the 125 grain offerings delivers performance very similar to the venerable 7.62×39 cartridge. This makes the 300 Blackout potent enough for a wide range of shooting tasks, from certain tactical applications to many short range hunting situations involving medium-sized game. The ability for many 5.56mm/223 systems to be switched over to the 300 Blackout, merely by changing barrels, makes this an incredibly versatile combination. Lapua brings over nine decades of case manufacturing knowledge, precision and quality to the new Blackout, assuring the shooter of the very best performance.”
7mm-08 Remington Brass
 Lapua notes that it’s new 7mm-08 brass is made to very high standards, benefiting hunters as well as competitors: “The 7mm-08 came to dominate the High Power Silhouette rifle game shortly after its introduction, offering a superb combination of power, light recoil and accuracy. Since then, it has also been used to win National Championships in High Power competition, and become a staple for hunters as well. With ballistic performance exceeding that of the time honored 7x57mm Mauser, but suited to a shorter action, the 7mm-08 is an ideal cartridge for most big game hunting. Lapua brings… state-of-the-art manufacturing methods, combined with old world craftsmanship, to the production of these cases. Primer pockets and flash holes are held to strict tolerances to withstand repeated firings and reloadings. After final necking of the case, they are finished with the proper anneal [for] accuracy and durability.” Lapua also notes that it offers two new 7mm Scenar bullets, which will work very well in the new 7mm-08 cartridge brass.
8x57mm JS Brass
Last but not least, Lapua is producing 8x57mm JS brass. Lapua notes that: “When the 8x57mm JS cartridge was introduced in 1905, its innovative use of a high velocity and relatively light weight pointed bullet design revolutionized infantry combat. An outgrowth on the original 8x57J military round, the 8x57mm JS round served the German military in both world wars, and became a popular sporting cartridge in any area where there was a strong German influence. From African plains game to European stag and boar, the 8mm Mauser has earned an enviable reputation as a big game round in a wide array of conditions. Accurate, versatile and powerful, the 8x57mm JS still serves the sporting community well for a host of hunting applications. In answer to the requests of the many devotees of this fine cartridge, Lapua is pleased to announce our introduction of the new 8x57mmJS case. The new 8x57mmJS will deliver the same accurate, reliable performance for which Lapua cases are world renowned. This means tough, durable cases that will not only withstand repeated loadings, but retain their accuracy shot after shot. [Lapua’s 8x57mm JS brass offers] very tight tolerances in neck wall concentricity and overall uniformity.”
See Lapua’s New Products at SHOT Show 2015
If you plan to attend SHOT Show in Las Vegas, stop by and visit the Lapua Exhibit (booth #11929). With luck, samples of the new 7mm-08, 300 BLK, and 8×57 JS brass will be available to view. Lapua engineers will be on hand to talk about Lapua brass and bullets, and explain the production processes that make Lapua brass so durable and consistent. In recent years, in the world of centerfire competition, Lapua brass has absolutely dominated the winner’s circles as well as the record-books.
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August 3rd, 2014
Need something for the walls of your “man cave” or reloading room? Check out these jumbo-size cartridge posters. The creators of the Cartridge Comparison Guide now offer three very large full-color printed posters. These can be tacked to a wall or matted/framed to hang like paintings. Three different posters are available.
Rifleman’s Classic Poster (38″ x 27″)
The Rifleman’s Classic Poster, a full 38 inches wide and 27 inches tall, is the most comprehensive. This $19.95 poster displays 272 rifle cartridge types at true size (within 4/1000 of an inch). Cartridges shown range from .17 caliber all the way up to the big boomers (including some cannon shells). The Rifleman’s Classic poster includes all American Standardized Rifle Cartridges (as of 2013) and many European rifle cartridges. The poster is a good representation of military cartridges dating back to WWI and includes cartridges such as the 13X92mm MSR and the .55 Boys.
CLICK Image to Enlarge:
American Standard Cartridge Poster (Rifle, Handgun, Shotgun) — $15.95
The 36″ x 24″ American Standard Poster displays 165 rifle cartridges, 55 handgun cartridges, and 9 different shotgun gauges. This includes all American Standardized Cartridges (rifle, handgun, and shotgun) available as of January 2012. All cartridge types are displayed in full color, actual size. The rifle selection includes all standard hunting cartridges from the 17 Mach 2 through the .505 Gibbs and .577 Nitro. Bonus cartridges include the .375 and .408 Chey-Tac, .416 Barrett, .50 BMG, 50-20 and 20mm. The Handgun section covers cartridges from the 17 HMR to the 500 S&W. Shotgun cartridges include the .410 and 32 gauge up to the 8 gauge. NOTE: Wildcat, proprietary, and obsolete-historic cartridges are NOT included in this poster.
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BIG BORE Cartridge Poster (215 Cartridges) — $15.95
The 36″ x 24″ Big Bore Poster illustrates over 215 large=caliber rifle cartridges, all shown actual size in full color. These include Standard, Historic, Military, Proprietary and Wildcat rifle cartridges side by side. Cartridges illustrated range from the subsonic .338 Spectre up to the monstrous .729 Jongmans. The poster also includes historically significant cartridges such as the 12 Gauge Paradox, 4 Bore, 1″ Nordfelt, 50 BAT Spotter, .50 BMG, .5 Vickers, 12.7×108 Russian, 20mm, 25mm, 30mm and more.
CLICK Image to Enlarge:
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April 6th, 2014
As a cartridge case is reloaded multiple times, burnt powder residue and carbon builds up on the inside of the case. Unless the case interior is cleaned in some fashion, eventually you’ll see a reduction in case capacity. One of our Forum members from Australia wonders about the effects of reduced case capacity: “If the capacity of the case decreases as the crud builds up, then it effectively reduces the chamber size. Wouldn’t that change the pressure produced from that of an equivalent clean case?”
Ultrasonic Cleaning Example:
Interesting Test of Case Capacity Changes
Forum member Fred Bohl has actual test results that can help answer the above question. Fred proved that, over a 20-reload cycle, the case capacity of uncleaned cases did, indeed, decline a small amount. However, surprisingly, this did not seem to affect the actual chronographed velocity of the load. ES did increase, but Fred believes the higher ES was due to changes in case-neck tension, rather than due to the slight reduction in case capacity.
Fred reports: “Back when beginning to use ultrasonic case cleaning, part of the motivation was to get the inside clean based on the assumption that allowing burnt residue to build up inside cases would affect capacity, and, ultimately, performance. An experiment was done to test this hypothesis. The load used, 30.5 grains of RL15 behind 107gr SMKs in a 6mmBR, was selected for best group and lowest ES in prior load development. It turned out to be 92% of initial case capacity and neither “full” or compressed. (I would suspect that different powders, load weight, and total case capacity might produce very different results.)
We took 30 cases of identical initial capacity and tracked three lots of 10 each:
LOT 1: No Internal cleaning
LOT 2: Cleaned with media in tumbler
LOT 3: Cleaned with Ultrasound machine
Each case (in each lot) was shot and reloaded 20 times. The simplified results after 20 reloads of each lot were as follows:
Lot 1 (not cleaned) – 0.3 to 0.4 gr. loss of capacity, 5 to 8 fps greater ES.
Lot 2 (tumble cleaned) – 0.1 to 0.3 gr. loss of capacity, 4 to 6 fps greater ES.
Lot 1 (ultrasonic cleaned) – no loss of capacity, no detectable change in ES.
FINDINGS
There was no detectable correlation of velocity change to the lots. An oddity was that on very hot days Lot 1 velocities were, occasionally, slightly higher. [Editor’s note: That does suggest that the carbon build-up inside the uncleaned cases might cause a slight increase in pressure that shows up on hot days. Fred has posted that “A local shooter reported doing the 20 reload, no clean test on a .308 that gave a loss of capacity of 2.0 grains, doubled ES and signficant velocity changes. However, I don’t have any details on his load weight or powder.”]
NOTE: From results of another ongoing test, I believe the above differences in ES are probably due more to variance in bullet grip tension than case capacity. The ultrasound cleaned cases (LOT 3) did maintain the lowest ES, but we are not 100% sure of the reasons why. More consistent bullet seating might be the reason.
[Editor’s comment: Jason found that with his ultrasonically-cleaned cases, the inside of the necks got so “squeaky clean” that he needed to use dry lube in the necks. Jason uses the $10.95 dry lube kit from Neconos.com. This applies ultra-fine Moly powder to the neck using small carbon steel balls]
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March 25th, 2014
The “Old Warhorse” .30-06 Springfield cartridge is not dead. That’s the conclusion of Forum member Rick M., who recently compared the 1000-yard performance of his .30-06 rifle with that of a rig chambered for the more modern, mid-sized 6.4×47 Lapua cartridge. In 12-16 mph full-value winds, the “inefficient and antiquated” .30-06 ruled. Rick reports:
“I was shooting my .30-06 this past Sunday afternoon from 1000 yards. The wind was hitting 12-16 mph with a steady 9 O’clock (full value) wind direction. My shooting buddy Jeff was shooting his 6.5×47 Lapua with 123gr Scenar bullets pushed by Varget. Jeff needed 13 MOA left windage to keep his 6.5x47L rounds inside the Palma 10 Ring. By contrast I only needed 11.5 MOA left windage with my .30-06. I was shooting my ’06 using the 185gr Berger VLD target bullet with H4350. I managed the same POI yet the .30-caliber bullet only needed 11.5 MOA windage. That’s significant. From this experience I’ve concluded that the Old Warhorse ain’t quite dead yet!”
Rick likes his “outdated” .30-06 rifle. He says it can deliver surprisingly good performance at long range:
“To many of the younger generation, the Old Warhorse .30-06 is ‘outdated’ but I can guarantee that the .30-06 Springfield is a VERY ACCURATE cartridge for 1000-yard shooting (and even out further if need be). With some of the advanced powders that we have today, the .30-06 will surprise many shooters with what it’s capable of doing in a good rifle with the right rate of twist. My rifle has a 1:10″ twist rate and I had it short-throated so that, as the throat erodes with time, I could just seat the bullets out further and keep right on shooting. My recent load is Berger 185gr Target VLDs pushed by IMR 4350. This is a very accurate load that moves this bullet along at 2825 fps.”
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March 20th, 2014
This new tool trims cases quickly, with precision control over case length via a micrometer-type dial. The folks at ACT Tactical have developed an easy-to-use compact case trimmer called the TRIM-IT. Crafted from 6061-T6 aluminum, this sturdy case trimmer comes with a 100% lifetime guarantee. The $97.50 TRIM-IT features a micrometer that’s built into the unit itself. Caliber-specific inserts (called “Caliber Dies”) index off the case shoulder.
The TRIM-IT can work with any hand-drill or drill press. Once you get the hang of it, you can trim a case in 7-8 seconds — that gives you a production rate of 400+ cases per hour. The TRIM-IT delivers repeatable precision to plus/minus one-thousandth. This unit also holds its cut-length setting, unlike some other trimmers which require frequent adjustment.
The basic unit ships with two caliber dies, for .223 and .308. Other listed caliber dies include 6.8 SPC, .300 BLK, .30-06, 30-30 Win, 300 Win Mag, 7MM REM, 7.62x54R, and 8MM Mauser. Other cartridge types can be custom-ordered from EZTrimit.com. To change dies, simply loosen the set screw on the TRIM-IT, take the caliber die out, add another one, and tighten the screw — quick and easy.
The built-in micrometer is great. The handy dial gives you a positive, repeatable length setting quickly — no fiddling with locking rings or spacers. Once you get the ring set properly, the cut lengths are consistent from the first case to the last. Expect your case OAL spread to be about +/- .001″ (starting with full-length-sized cases with uniform rim to shoulder lengths). For more information, email sales [at] eztrimit.com or call (562) 602-0080. You can see how the Trim-It device works in the video below.
Video Shows Trim-it Set-Up and Operation
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March 2nd, 2014
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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