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Author: John Barsness / Wolfe Publishing Co.
Date: Jun 21 2005
“Improved” cartridges have been around ever since Lisle Kilbourn cut a .22 Hornet chamber with a sharp shoulder and fired a standard Hornet case, resulting in slightly more powder capacity – and velocity. The process has since been applied to hundreds of cartridges. In fact, some factory cartridges are improved versions of other factory cartridges, notably the .300 Weatherby Magnum, an improved version of the .300 H&H Magnum.
These days it seems that every time we turn around, another cartridge has been “Ackley Improved.” Gunsmith P.O. Ackley experimented with improving various rounds in the 1950s and 60s, all with a 40-degree shoulder. He found that most of the time the process wasn’t worth the trouble, but his name caught on and today is applied to any improved cartridge with a 40-degree shoulder, whether P.O. ever made one or not.
There are advantages and disadvantages to Ackley Improving any cartridge. The most obvious advantage is more powder room, hence higher potential velocity. Just how much extra velocity is possible depends on the original cartridge. Rounds with tapered bodies and sloping shoulders gain the most, the reason the earliest improved wildcats were based on rounds such as .22 Hornet, .250 Savage and .300 H&H Magnum.
Here we must remember that potential velocity only increases at one-fourth the rate of any powder capacity increase. The .300 Weatherby Magnum gains about 13 percent in powder capacity over the .300 H&H, which translates into a 3.2 percent gain in muzzle velocity, everything else being equal. This means that if a 180-grain bullet can safely be pushed to 3,000 fps in a .300 H&H, it can be given about 3,100 in the .300 Weatherby – in an equal-length barrel at the same pressure.
I emphasize the last because .300 Weatherby factory ammunition has always been advertised as gaining 250 to 400 fps over the .300 H&H. This is because .300 H&H ammunition has been loaded to much lower pressures for many years, especially when compared to original .300 Weatherby ammunition, which was stoked to the gills.
But look up both cartridges in a modern loading manual that pressure- tests each round, and you’ll find the difference isn’t all that much. Nosler’s manual, for instance, lists the top velocity for a .300 H&H 180-grain load as 3,023 fps, while with the .300 Weatherby the top 180 load gets 3,185 fps.
This seems to favor the .300 Weatherby by more than 100 fps, but now let’s look at barrel length. The H&H was tested in a 24-inch barrel, the Weatherby in a 26-inch tube. Most magnum cartridges gain or lose about 30 fps per inch of barrel. Subtract 60 fps from the Weatherby data, and we get 3,125 fps, 102 fps faster than the .300 H&H data.
Another advantage of improved cartridges is that, unlike other wildcats, factory ammunition can still be fired if necessary. Also, the 40- degree shoulder of the Ackley Improved rounds cuts down on case stretching enormously, so cases rarely have to be trimmed. This can be a considerable advantage to a varmint shooter, for instance, who often loads hundreds if not thousands of rounds a year.
The disadvantages of the Ackley Improved cartridges start with fireforming. This is easily done in a varmint rifle, where hundreds of rounds of factory or conventional handloads can be shot at prairie dogs, but not so easily (or economically done) otherwise. Also, most Ackley chambers are cut by running a reamer into a conventional chamber. This results in a new chamber that’s slightly loose with factory brass. If a factory round or newbrass handload is fired here, the case is driven into the chamber by the firing pin, then stretches upon firing, often ruining the case. The solutions are to seat a bullet out so that it contacts the lands, thereby holding it against the blow of the firing pin, or to form the case with some fast-burning powder under a loose “bullet” of uncooked cornmeal. Tilt the rifle skyward while loading the chamber, and pop! New case!
An even better solution is to have the barrel turned back one thread before rechambering, so that the chamber exhibits a slight “crush fit” with new brass. Then any sort of factory or new-brass handload can be fired, and cases will be formed perfectly.
Another disadvantage to improved rounds is that any rechambered rifle loses at least $100 of its value right then and there, since wildcat rifles are not popular among the general public. A custom rifle by some known maker, however, will hold its value better.
The last disadvantage of most improved cases is lack of pressure tested loading data. While a few improved rounds have been popular enough to interest the major bullet and powder companies that publish most loading manuals, they are few, generally limited to the .22 K Hornet and the .257 Roberts, .280 Remington and .30-06 Ackley Improved. So how is the home handloader going to load his new 6mm Remington or .35 Whelen Ackley Improved safely?
It’s actually relatively easy. First, fireform a case with a safe load. This can be a mid-pressure load for the standard cartridge. Now, weigh that case, then fill it full of water and weigh it again. The difference in the two weights is the water capacity of the case.
Next do the same thing with a standard case. Now we know the difference in water capacity between the standard and the Ackley Improved case. Using your pocket calculator, divide the case capacity of the Ackley case by the case capacity of the standard. In this instance, let’s use the 6mm Remington. We find that the standard 6mm holds about 55.0 grains of water, the "Ackleyed" 6mm about 59.5 grains. Divide 59.5 by 55.0 and we get 1.08, which means the 6mm Ackley has about 8 percent more case capacity than the standard 6mm.
Now we divide 8 percent by 4 (remember our ballistic rule of one fourth?) and we get 2 percent. This is about how much velocity gain you’ll get out of a 6mm Ackley Improved – provided it’s loaded to the same pressure as the standard .257. This comes to 60 fps in a 3,000-fps load.
Now we start loading fireformed 6mm AI cases. Here we can safely start with near-maximum 6mm Remington data, because the 6mm Ackley case will result in lower pressure. As we test loads with more and more powder, we watch the chronograph carefully, and when our new 6mm Ackley gets about 60 fps above 6mm Remington muzzle velocities (allowing for barrel length), we can assume we’re operating at about the same pressure.
So now you know how to safely use manual data to work up loads for an Ackley Improved cartridge.
Sixty feet per second doesn’t sound like much, does it? Well, it isn’t, but it’s about what you can safely expect in Ackley Improved versions of most modern cartridges with reasonably parallel-sided cases and shoulders of at least 20 degrees. This is because Ackley Improving such a round doesn’t gain very much case capacity. The cartridges that gain the least have the narrowest shoulders. The .35 Whelen Ackley Improved, for instance, gains almost nothing in case capacity over the standard .35 Whelen, simply because there isn’t much shoulder to blow out.
Despite all this, some great gains in muzzle velocity are claimed by folks with Ackley Improved rifles. I know a guy who claims a gain of 250 fps with his .35 Whelen Ackley Improved with 250-grain bullets. But this gain is over factory ballistics of 2,400 fps, and the standard factory Whelen isn’t loaded very warmly. My friend’s Ackley Improved model also has a 26-inch barrel, and he’s loading it very warmly, surely in excess of 65,000 psi. Here almost all the velocity gain comes from extra pressure and a longer barrel, not the almost nonexistent extra case capacity of the .35 Whelen Improved.
All this may sound like I’m down on Ackley Improved cartridges. Well, yes, I am. I’ve owned several, and never found the slight velocity gains worth the disadvantages. Now, if you shoot prairie dogs by the hundreds each year, a .223 Ackley Improved is a great cartridge – not because it gains any significant velocity over the standard .223, but because you don’t have to trim cases. But if you desire more velocity than a standard big game round such as the .30-06 can provide, it makes more sense to buy (or build) a rifle for the next factory round up. Any sort of .300 magnum will produce more velocity than the .30-06 Ackley Improved and be worth more if you want to sell it.
(1) A .25-06 Remington factory load, (2) a case after being fired in the chamber, (3) a fired case after neck sizing and (4) a loaded .25-06 Ackley Improved cartridge.. The parent cartridge is then fired in the improved chamber, resulting in a new wildcat cartridge.. He explained the increased capacity of the improved case with some incorrect figures, such as stating the diameter of the improved case at the shoulder is .460 inch, when all Ackley Improved cases based on the .30-06 size case head are listed as .453 to .454 inch, depending on source.. Following Waters’ suggestion, more or less, five rounds were loaded with IMR-4831 under the Speer 120-grain bullet with Federal 210 primers and powder charges that ran from 48.0 to 55.0 grains.. My best Ackley Improved load of 53.5 grains under the same bullet produced a diameter of .4745 inch.
Fire-formed 223 Ackley Improved case (left) and fired 223 Remington case (right).. Cartridges improved by Ackley, are known as Ackley Improved (sometimes designated by only the word Ackley or Improved).. For instance, an improved version of the 280 Remington would be known as a 280 Remington Ackley Improved or 280 AI.. This would provide a safe chamber dimension for the fire forming the parent cartridge brass in the improved chamber, while requiring minimum work to improve a rifle barrel.. The downside to this method was that firing the parent cartridges in the improved chamber would often provide inaccurate results and the parent case would stretch to the longer length when the case obturated against the chamber wall.. Some smiths turned back the barrel tenon one thread, reset the shoulder, and chambered the barrel with a headspace dimension .004″ short of minimum so that the parent cartridge would be supported at the neck shoulder junction and provide improved accuracy and less case stretching when fire forming.. To properly headspace barrels chambered in this method, Dave Manson, of Manson Reamers makes specialized Ackley Improved go gauges.. When using one of his improved go gauges, the bolt should close on the Improved go gauge.. Setting back the shoulder .0625″ will allow me to chamber the barrel and have the existing barrel markings index back to where they started.. I use a tapered range rod to make sure the barrel is aligned in the same manner as it was the first time I cut the chamber.I use a number of different methods to align barrels.. You can’t use a piloted counter bore in this situation because the chamber has already been cut, the pilot has nothing to follow.I check to make sure the bolt fits in place.223 Improved go gauge (left), 223 Remington go gauge (center), and 223 Remington no-go gauge (right).. The 223 Remington go gauge will be used as a no-go gauge for the improved cartridge.I set up a Mason piloted 223 Improved reamer in a floating reamer holder with an adjustable reamer stop.. I selected a floating holder to allow the reamer to follow the existing chamber.When the reamer stop reaches full depth, I check my progress.With the go gauge in the chamber, I use feeler gauges to determine how much deeper I need to cut the chamber.When the bolt closes on the 223 Improved go gauge, and doesn’t close on the 223 Remington go (shown here), the chamber is the appropriate depth.Here is a piece of unfired brass that that has had its neck coated with marker.. Here is a Winchester 5.56mm 62 OTM cartridge (left), next to the fire formed brass (right).Fire-formed 223 Ackley Improved case (left) and fired 223 Remington case (right).. The improved case (left) doesn’t have a tapered body and has its shoulder moved forward at a sharper, 40 degree (versus 20 degree) angle.I would say this rifle shoots well even when fire forming.
To be Ackley Improved or not to be Ackley Improved?. Reader K. Akins recently wrote to ask which cartridge I thought would benefit the most from conversion to Ackley Improved:the 260 Remington, 270 Winchester, or 7mm-08 Remington.. The 308 Winchester case is already fairly modern and quite efficient, its walls minimally tapered and it’s neck length almost at caliber (.303”) for a secure, straight grip on long bullets.Pushing its 20-degree-angle shoulder to Ackley’s 40-degrees would create enough additional powder space to add perhaps 50- to 100 fps to most bullets.. Photo shows 270 WSM ammo, a modern cartridge with Ackely Improved ballistic performance.. Ackley Improved group at 100 yards. J. Frischkorn read my Swarovski dS super scope (rangefinder, electronic, and digital — you can read details in this blog) and that prompted this question: “Prior to using these new “super scopes” how good were you at range estimation, Ron?. Zero a modern cartridge with efficient bullets 2.5” to 3" high at 100 yards and you stay inside the 10" kill circle from muzzle to 300 yards.. In my opinion the two biggest things to remember about Ackley Improved cartridges and long range shooting is that neither are necessary to be a successful hunter.. In doing this we are free to select how we shall hunt: long range rifles and laser range-finding scopes or lever-action 30-30s with open sights or flintlock muzzleloaders, bows, spears, slingshots… Within the laws, rules, and regulations of our various states we are free to draw a line in the sand and play the hunting “game” as we wish.. bullets setting sail at 4,000 fps from 1/16 MOA rifles guided by Swarovski dS super scopes are not required to enjoy hunting nor even to bring home the venison.. Even if you never hunt anything but steel plates with them, super scopes and super rifles throwing super bullets are interesting and fun.. Mr. Spomer has hunted with sling shots, spears, recurve bows, compound bows, air guns, cap lock muzzleloaders, iron-sight revolvers and autoloaders, 19th century lever-actions, 20th century scoped 30-06 bolt-actions and autoloaders, some of today's most elaborate super rifles and scopes, and everything in between.
Problem is that with rimmed cases this is not true, as long as the headspace for the parent case is correct and the new chamber will clean up the original chamber.. As long as the case design will allow the case to be extracted the case can be much smaller than the chamber and it will fire-form just fine.. Just as the rim above holds the case during forming, here the belt holds the case while the body and new shoulder are formed in the improved chamber.. The basis for most of the confusion about head spacing for Improved cases comes from the fact that the rimless cases do require that the barrel be set back to get a proper new chamber.. The reason for this is really simple, Ackley was a pretty smart guy, he figured out that by shortening the chamber by .004” you would still be able to chamber factory loads but with his sharp shoulder and expanded body the only place the case would touch in the new chamber was the bolt-face and the junction between the neck and the shoulder of the case.
Then, in 2019, Hornady introduced a 162-grain ELD-X bullet loaded in the .280 AI, adding it to the excellent Precision Hunter line of ammunition.. Factory data has it exiting the muzzle at 2,850 fps, just 90 fps slower than the same bullet in Hornady’s 7mm Remington Magnum ammo.. Nearly concurrently, Federal announced it was working on three different .280 AI loads, including a Berger bullet and Federal’s own Terminal Ascent and Trophy Copper bullets.. Four of Joseph’s favorite bullets for the .280 Ackley Improved are (left to right) Hornady 175-grain ELD-X, Berger 168-grain VLD Hunting, Federal 155-grain Terminal Ascent, and Barnes 139-grain LRX.. If you have a rifling twist that’s fast enough, the .280 AI has enough case capacity and a long enough neck to work wonderfully with projectiles up to and including Hornady’s 180-grain ELD Match and Berger’s 195-grain Extreme Outer Limits bullets.. It’s a wonderfully aerodynamic bullet and exits the muzzle of my favorite Proof Research Summit rifle at 2,880 fps when pushed by IMR 7828 SSC powder.. It’s a legitimate, repeatable 0.40-MOA bullet in my Proof rifle, and even though velocity with that tuned handload is modest, at 2,870 fps, it has proven to be excellent on mule deer and elk.. A technician friend at Barnes used this bullet right after it was introduced for a once-in-a-lifetime free-range bison hunt in Utah and shot a large, old bull right at 600 yards with his .280 AI rifle.. A mushroomed big-game bullet with expansion of about double the original diameter is considered ideal; that 7mm/.284-diameter bullet measures 0.568 inch across, with a surface area of over 1.01 square inches.
He stated that the Ackley Improved cartridge “…shared the same dimension (as the parent round) from the boltface to the junction of the shoulder and neck.. I decided to call upon the knowledge of two longtime reloading mentors (ST columnist Allan Jones and former ST Rifles/Reloading Editor Rick Jamison) and the Nosler R&D Manager Mike Lake (Nosler sells factory-loaded .280 AI ammunition and rifles chambered for .280 AI).. I pointed out that the Wolfe Publishing drawings indicated the neck length of the .30-06 case was 0.388 inch and the .30-06 AI case neck length was 0.419 inch, meaning the parent round’s neck was thirty-one thousandths shorter than the AI version.. The standard round’s sloping shoulder could never touch the AI chamber shoulder before firing.. So the neck-shoulder junction of the parent cartridge must reach the AI chamber neck-shoulder with at least a slight crush so it would reliably fire.
Ackley obviously had the pedal to the metal, because his top published velocity of 3,271 fps with a bullet of that weight in the .250 Improved is considerably faster than the larger .257 Roberts is commonly handloaded to, and about as fast as maximum loads in the even larger .25-06 Remington.Low velocity spreads of all loads using the Federal GM210M primer indicate uniform propellant ignition and burn.. This also becomes quite evident when perusing velocity differences between improved cartridges and their parents in today’s reloading manuals.My experience with the .250 Savage Improved goes back to 1981, when I sent a 1970s vintage Weatherby Varmintmaster to Oregon gunsmith Robert West.. When 100-grain bullets are loaded to maximum pressure and fired in 24-inch barrels, the .250 Savage Improved is about 100 fps faster than the standard .250 Savage, and about 300 fps faster than Hornady’s factory load.. When designing his cartridge, Ackley headspaced the body/shoulder junction of a .250 Savage case on that same point in the chamber, just as he did with his other improved cases.. Hornady shows 2,850 from a 26-inch barrel; Western Powders maxed-out at 2,781 fps from a 24-inch barrel; Barnes technicians squeezed 3,072 fps from a 24-inch barrel and Lyman’s 24-inch barrel stopped at 2,985 fps.. Nosler reached 2,950 fps from a 22-inch barrel; over at Speer, a 24-inch barrel was good for 3,026 fps and Hodgdon’s 24-inch barrel delivered 2,936 fps.. Cases have traditionally been formed by firing .250 Savage loads in a .250 Improved chamber, but simply running the 6.5 Creedmoor case through the .250 Improved full-length resizing die works well and eliminates the need for fireforming.. Headspacing of cases formed from the Creedmoor was perfect for Layne’s rifle, but since the .250 Improved is a wildcat without standardized case dimensions, headspace with a simple neck-down may not be correct for other rifles.. These cases include (left to right): a .250 Savage, .250 Savage after fireforming in an Improved chamber, 6.5 Creedmoor case necked down for .257-inch bullets and a loaded .250 Improved cartridge.. average of the velocities from those seven sources is 2,944 fps.When loaded to maximum safe pressure for a modern bolt-action rifle, I find the standard .250 Savage to be capable of pushing a 100-grain bullet to 2,900 fps from a 22-inch barrel, and the 24-inch barrel of my Remington Model 700 Classic provides 3,000 fps without stress or strain.. Most of my .250 Improved loads with 100-grain bullets exit the 24-inch barrel of my rifle at around 3,100 fps.. Maximum handload velocities with 100-grain bullets in the 22-inch barrel are usually around 3,100, so my .250 Improved with a 24-inch barrel is about as fast as my .257 Roberts with a 22-inch barrel.. Whether or not the velocity gained by blowing out the .250 Savage case is worthwhile is debatable, but there is one thing that is not: As velocity with a 100-grain bullet begins to exceed 2,700 fps, considerable body taper in the standard case causes it to lengthen quickly, and the higher the chamber pressure, the faster it grows.. The 1:10 twist of my rifle does not like bullets longer than that, so a 1:9 twist would likely be the way to go.If the .250 Savage Improved was introduced today, it would be called the “.25 Creedmoor.” With the exception of their neck diameters, the 6.5 Creedmoor and .250 Improved cases are quite close to the same.
Back in 1965 I had the late, great Bill Marden build me a rifle using a new commercial FN Mauser action, fitted with a Sako barrel some 600mm long, chambered in 6mm Ackley Improved.. At least I didn’t until in July 2012 I was offered a Mauser rifle with worn out barrel, a 3-die set in 6mm Ackley Improved and a new Hogue stock to suit.. To tell the truth I was embarrassed when I read the list of estimated velocities for my loads which credited the 6mm Ackley with bullet speeds that would strain the .240 Weatherby.. But this was in the days before cheap chronographs became available and the velocities were probably taken from Ackley’s Handbook which contains a lot of over- optimistic data, including Mashburn’s figures for his .244 Improved which listed some unrealistic figures – up to 3450fps with a 100gn bullet!. Taking its place alongside my hot .220 Wilson Arrow, long- ranging .240 Weatherby and .25 WSM, the 6mm Ackley adequately fulfills the twin roles of a simonpure varmint rifle and a medium-calibre big game rifle.. Today, Remington no longer chambers any rifles for the 6mm Remington, but the .243 is chambered in 26 different variations in “Big Green’s” wide range of rifles.. A good many older cartridges can be improved in design to produce more efficient burning of modern powders, but any increase in velocity is usually quite modest – usually 100-150 foot-seconds.. The case holds about 10-percent (5 grains) more powder than the standard 6mm Remington, thus only a modest increase in velocity is possible and requires a considerable increase in the amount of powder burned.. After carrying out considerable experimentation with improved cartridges, my conclusion is that while combustion is improved, there is little increase in velocity without reaching higher pressures.. Another advantage of a sharp-shouldered case is that it creates greater resistance to the burning powder, holding more of it back in the case during the burning process, thus preventing unburned powder granules from being blown out into the throat of the chamber to give a sand-blasting effect.. My opinion of the 6mm ackley Improved (or any other improved cartridge) is that while it gains better combustion and longer case life, accuracy doesn’t enter into the equation since it is affected more by the quality of the barrel, chamber and reloads.. Loads in the table all proved safe in my rifle and most of the powders gave a high load density, but even the slowest burning numbers are only lightly compressed.. It has a sufficiently large boiler room to load the heaviest 6mm bullets and slower burning propellants for use on big game, while for small varmint and predators at extreme distances, the lighter bullets are devastatingly effective.
When you read this, do not, pray, confuse “overrated” with “bad” or “unsuccessful.” The 9mm Parabellum, for example, is one of the most popular and heavily produced cartridges in the world, and has had a long, long life.. It’s effective in submachine guns and, with the most modern bullets, does OK in handguns.. Police departments like it because ammo is cheap, and because it kicks very little.. Very short cartridges with hardly any case taper and sharp shoulders have been overwhelmingly successful in competition shooting where they are single-loaded.. There is a 7mm magnum with true magnum performance, but Weatherby makes it, not Remington.. This round was designed for the FBI when the Bureau found the 9mm woefully inadequate.. Unlike the .45 ACP, which can be shot very quickly and very accurately, the 10mm can’t.. It fires a big bullet at high velocity, and is still far too powerful for police work, but at the same time it lacks the potency of the .44 Magnum on game.. Ackley hit on a formula for increasing the powder capacity of standard cartridges by blowing them out in an “improved” rifle chamber.. On the one hand, it’s more powerful than the .22 LR, but on the other, it gives you only 25 yards (or so) more effective range.. The rifle comes back so quickly that you can’t roll with the punch.
We glom onto rifle cartridges which aren't that great while ignoring those rifle cartridges that have something very real to offer.. With the exception of perhaps the dangerous game rifle segment, mountain guns are the most specialized group of sporting rifles.. There is always a balance between designing rifle cartridges that shoots flat enough and hits hard enough to kill sheep, goats and elk at long range, is light enough to carry at high altitudes all day and yet produces a manageable level of recoil.. Ackley, who set out to better the performance of standard rifle cartridges by pushing the shoulder forward and steepening shoulder angle while maintaining the headspacing dimensions from the original cartridge, allowing the shooter to safely fire the parent cartridge in the improved chamber.. That's a shame, because the .358 Shooting Times Alaskan, a rifle cartridge designed by Layne Simpson and introduced in 1992, has a tremendous amount to offer the hunter pursuing large game, such as elk, moose, eland and the like.. case, drives that same bullet at nearly 3,000 fps, making it a real contender for the title of the most versatile heavy rifle cartridges for North American game.. The .404 Jeffery has a long history on African game, and CZ now offers the rifle in its Safari Classics Magnum Express line with a Mauser-style action, so the .404 may start appearing more on the African game fields where it earned its reputation as a competent, shootable rifle cartridge.