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.17-Caliber Reloading Data and History for 5 Cartridges

The .17 caliber is the little centerfire that could — and can and does — perform in the varmint fields.

.17-Caliber Reloading Data and History for 5 Cartridges

Parker Otto Ackley wore many different hats. He was a college professor, a gifted machinist, a writer, a barrel maker, a bullet maker, a builder of rifles and an avid experimenter. But he became best known for the development of wildcat and improved cartridges bearing his name. Ackley and others began developing centerfire cartridges smaller than .22 caliber soon after the end of World War II, and they really got busy during the 1950s. A few .12 and .14 calibers emerged, but those of .17 caliber ended up being the most popular.

I got to know Ackley while he was doing some rifle work for me during the 1960s and ’70s. By that time most of his hearing was gone, and his daughter would answer the phone and relay the conversation back and forth between her father and the caller. During one of those conversations, I requested samples of any sub-caliber wildcats Ackley might have on hand. Expecting to receive a half-dozen or so, I was quite surprised after opening the package to see more than 30 different cartridges ranging in size from the .17 Lilliput on a shortened .22 Hornet case to the .17 Swift on the full-length .220 Swift case.

A number of the cartridges were Ackley’s designs while the others had been sent to him by various other developers for inclusion in his two-volume Handbook For Shooters & Reloaders.

Ackley created his first .17 caliber wildcat by necking down the .30 Carbine case. He called it the .17 Pee Wee and built a dramatically scaled-down 1917 Enfield action specifically for it.

.14 Lilliput, .14 Wasp, .14 Hornet, .17 Pee Wee and .17 Ackley Hornet
Ackley’s first two .17s were the .17 Pee Wee (second from r.) and .17 Ackley Hornet (far r.). He also developed some .14 calibers, which never caught on (l.-r.): .14 Lilliput, .14 Wasp, .14 Hornet.

His most successful wildcat, the .17 Hornet Improved, requires an RCBS die set for forming the case. The first die necks a .22 Hornet case down to .20 caliber. The trim die squeezes the neck down to .17 caliber, and its hardened surface allows squaring up the mouth of the case with a fine-tooth file. Chamfer and deburr the mouth of the case, run it through the full-length resizing die and the case is ready for fire forming with a reduced powder charge (I use a 20-grain bullet seated over 11.0 grains of H4198).

Based on reloading die sales at RCBS, Ackley’s .17 Hornet Improved is still one of the most popular cartridges of its caliber among varmint shooters. The other top-sellers are the .17 Mach IV, .17 Rem., .17 Fireball and Hornady’s .17 Hornet.

When developing its version of the .17 Hornet, Hornady shortened the .22 Hornet case about 0.050 inch to make overall cartridge length compatible with the magazines of existing rifles in .22 Hornet. A decrease in body taper gained back some of the capacity loss, but its gross water capacity is still about one grain less than for Ackley’s version. When both are loaded to maximum chamber pressures and fired in barrels of the same length, the Ackley cartridge is about 100 fps faster.

Using Hornady .17 Hornet brass to form .17 Ackley Hornet cases eliminates the need for case-forming dies. Simply run a case through the Ackley full-length resizer and it is ready to load.

During fire-forming the case will headspace on its rim and the shoulder will be moved forward to the Ackley position. After that, the die is set for head-spacing on the shoulder of the case. The neck of the case will be shorter than on cases formed from .22 Hornet brass, but accuracy is the same and flickertails don’t seem to mind.

Moving up in powder capacity, the .17 Mach IV was introduced during the 1960s by Las Vegas gunsmith Vern O’Brien, whose custom rifles were on the dainty Sako L46 action. Formed by necking down Remington’s .221 Fireball case and increasing shoulder angle to 30 degrees, O’Brien claimed a velocity of 3,700 fps for a 25-grain bullet.

I first became aware of his cartridge when reading a gun magazine article in the 1960s. The full-page lead photo was filled with two hunters, one tiny rifle and a huge Alaskan brown bear wearing a hide that surely squared 10 feet or better.

According to the story, O’Brien wagered that his guide could not kill the bear with his rifle in .17 Mach IV—and lost the bet. I recall wondering if close examination would have revealed several .375-inch holes the bear’s hide. Regardless, it was a foolish stunt.


I later bought an O’Brien rifle in .17 Mach IV, and after shooting it for about 10 years, I sold it to a collector. O’Brien also offered custom XP-100 pistols chambered for his cartridge, and the barrels were marked “.17 Mach III” to indicate lower velocity in the shorter barrel.

.17 Ackley Hornet, .17 Hornady Hornet, .17 Mach IV, .17 Remington Fireball, .17 Remington
These cartridges represent RCBS’s most popular .17 caliber reloading dies (l.-r.): .17 Ackley Hornet, .17 Hornady Hornet, .17 Mach IV, .17 Remington Fireball, .17 Remington

A form die set is required if .221 Fireball cases are used, but those lucky enough to find Remington .17 Fireball brass can simply run them through a .17 Mach IV full-length sizing die, add primer, powder and bullet, and head for the varmint fields. In 1970, O’Brien sold his company to Harrington & Richardson, which renamed the rifle the Model 317 Ultra Wildcat.

When introducing the .17 Remington Fireball in 2008, Remington copied the .17 Mach IV case with the exception of a couple of dimensions. The Remington case is about 0.006 inch larger in diameter at its body/shoulder juncture, and its head-space dimension is about 0.004 inch longer.

I have attempted to chamber Remington ammo in two .17 Mach IV rifles. The bolt on one would not close, and though the bolt on the other rifle would close, the fit was so tight a steady diet of that ammo would eventually cause galling of the locking lugs.

Dimensional differences between the two cases are so slight that load data for the two are interchangeable. The Berger reloading manual shows the exact same maximum powder charge weights for both. Starting and maximum charges vary slightly in the Hornady manual, but no more than to be expected from different lots of the same powders or slight differences in barrels, cases and bullets.

When it comes down to velocity, the .17 Rem. leaves the others choking on its dust. It is about 600 fps faster than the .17 Hornets and an honest 300 fps faster than the Mach IV and the Fireball.

Remington introduced it in 1971, and soon thereafter a friend of mine bought a Model 700 BDL chambered for it. This was before coyotes invaded the East and decimated the groundhog population, so we accounted for our share of them. I was shooting a custom Remington 40X in .220 Swift, and out to 300 yards my friend never failed to match me shot for shot. Beyond that distance, the Swift was the clear winner at bucking wind and dropping whistle pigs in mid-munch.

Years ago, a friend who worked at Remington informed me that more Model 700 rifles in .17 Rem. were shipped to Australian fox hunters than to dealers in the United States because it did not damage pelts as much as larger calibers.

In a precision-built rifle with a good barrel, the .17 Rem. can also be quite accurate. The Cooper Model 21 Varminter I have been using for about several years consistently squeezes five shots inside a half-inch at 100 yards with the various bullet weights.


Most .17 caliber bullets are much lighter than those of .22 caliber, and that makes them greatly dependent on high velocities for quick kills on varmints. Ballistic coefficients of those with plastic tips are considerably higher than the hollowpoints. I prefer 20-grain bullets in the .17 Hornets because they can be pushed much faster than 25-grain bullets. Same goes for the Mach IV and Fireball, although the velocity difference between the two bullet weights is less in them.

I prefer the 25-grain V-Max in the .17 Remington because it slices through wind a bit better than the 20-grain version, and it delivers more energy to boot. For called-in coyotes, I switch to the 30-grain Berger, but I prefer the 25-grain V-Max for longer shots.

How does the performance of the .17s compare with .22 caliber varmint cartridges? Zero the .17 Ackley Hornet with the Hornady 20-grain V-Max at 3,600 fps two inches high at 100 yards and it is two inches high at 200 yards and four inches low at 300. A 50-grain V-Max exiting the muzzle of a rifle in .223 Rem. at 3,400 fps and zeroed the same is down three inches at 100 yards.

Wind resistance? Drifts at 300 yards in a 10-mph cross breeze are 14 inches for the .17 Hornet versus 11 inches for the .223 Rem.

Moving to bigger cartridges, when the Hornady 20-grain V-Max exits the .17 Rem. at 4,300 fps and is zeroed two inches high at 100 yards, it is dead on the money at 300 yards. A 50-grain V-Max exiting the .22-250 Rem. at 3,800 fps has close to the same trajectory. Those are not huge differences in bullet drop and drift between the two bullet diameters, although the .22s do deliver more energy to the target.

WARNING: The loads shown here are safe only in the guns for which they were developed. Neither the author nor Outdoor Sportsman Group assumes any liability for accidents or injury resulting from the use or misuse of this data. Shooting reloads may void any warranty on your firearm.

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