Rechambered rifle a worthwhile task
By Don Lewis
Published: Friday, May 11, 2007,
While watching the edge of a hayfield that bordered a woods, a chuck appeared beside a discarded mowing maching that had been gathering rust for several years. It wasn't a long shot, but it was a perfect one to test my 22-250 Ackley Improved that had been a regular 22-250 since 1972. I'm sure the distance wasn't much more than 100 yards, but the Ackley Improved had just come off the 100-yard range where I had been shooting three-shot groups with three or four different load combinations.
The rechambered rifle had turned in a spectacular job on the paper targets from a benchrest, and now it was time to fire the first field test.
To step back in time for a moment, the 22-250 Ackley Improved is made by firing a conventional 22-250 round in the Ackley Improved chamber. This fire forms the case to a straight wall case (minimum taper) with a sharp 40-degree shoulder angle. This is a lot steeper angle than the factory 28-degree shoulder. There is a significant increase in powder capacity, but there's more.
Case stretching is probably the main demon plaguing the Remington 22-250 case. Due to the tapered body of the factory 22-250 round, cases are prone to stretch during the full-length resizing process. This problem can be partially corrected by using a neck die only or a full-length resizing die to just partially size the case. The 22-250 Ackley case design actually reduces case stretching.
Case trimming is a real nuisance especially when hundreds of cases are involved, and handloading varmint shooters often do production-type reloading. For instance, I reloaded more than 2,500 rounds of 223 brass in preparation for a prairie dog hunt. You can imagine how much time it required to hand trim more than 2,000 empties.
While on the subject of case trimming, I might add there are several ways of cutting down on the labor aspect. First, using an RCBS X-Die keeps cases from lengthening. The X-Die not only full-length resizes the case, it also limits the growth of the case. This eliminates the need for repeated trimming after the initial trim is done to standardize the case. The X-Die is not intended to shorten the length of the case; rather, as the case grows, the mandrel will reduce the normal rate of growth.
The second method is using a Dillon Power Case Trimmer. This powerful unit incorporates a high-speed cutter powered by a 1/4-horsepower motor. It has the standard 7/8x14 thread (same as conventional reloading dies) and can be used with any progressive or single stage press. Once set up and adjusted for a particular case, it trims instantly. Using Dillon's XL650 progressive metallic press with automatic case feeder, it's possible to trim around 20 cases per minute. After the shell plate is loaded, every pull of the handle trims a case and also sends a trimmed case flying into the case catch box.
Back in the 1930s, the 250-3000 Savage case was a favorite for wildcat experimenters. I can't recall all the creations that used the 250-3000 case as the basis for a new wildcat, but the 22-250 is the most prominent one. There were several versions of the 22-250 wildcat, and a gunsmith by the name of Jerry Gebby had a copyright on the name "Varminter."
The 22-250, even in its wildcat days, offers superb accuracy. It's inherent accuracy made it a favorite among benchrest shooters of that era. With all it had going for it, it's still hard to believe that it wasn't standardized by a factory many years back. Remington added it to its factory line in 1965 about 35 years after its inception. It's worth noting that Browning did chamber for the wildcat version. The various wildcats carried sharper shoulder angles from the 26 1/2-degree angle on the 250-3000 case. Remington standardized the 22-250 with a 28-degree angle.
The 22-250 outclassed all the other 224 caliber cartridges with the exception of the 220 Swift. The 22-250 was inherently more accurate at that time, but Swift fans never let up on the fact that the ol' Swift was the fastest cartridge available and therefore had to be better varmint round. To some degree, the argument is still going on.
At first, I decided to rechamber a Ruger heavy barrel 22-250, but since it was incredibly accurate, I felt it best to leave well enough alone. Back in the early 1970s, I helped an importer design a thumbhole varmint rifle to be manufactured by Dumoulin in Belgium. The rifle was never produced on a commercial scale due to a conflict with the manufacturer. I never learned what halted the project, but I firmly believe the rifle would have been a success. The prototype arrived stocked in nice wood and fitted with a Canjar trigger. It's possible the importer had the trigger installed in this country.
To make a long story short, he gave me the new rig for range testing and field evaluation. It didn't lack in accuracy, but I soon learned the rifle had a chamber problem. Even factory rounds were difficult to chamber. I had a custom rifle builder in eastern Pennsylvania check the chamber, and he said it was not cut to Remington's specification. Instead of doing a complete rechambering job by cutting off several threads to allow the barrel to turn a complete 360 degrees -- so the original base screw holes could be used -- the barrel was turned about one-eighth of a turn and the chamber "cleaned out." The original plugged screw holes were stiff visible above the forearm.
I finally decided to rechamber the Dumoulin outfit. Custom rifle builder Jim Peightal of Ernest ordered an Ackley Improved 22-250 reamer from precision reamer manufacturer Dave Manson, who owns Loon Lake Precision in Grand Blanc, Mich. The chamber cleaned out nicely, and fire-formed factory rounds or fairly strong powder charges in handloads perfectly.
Rechambering a conventional 22-250 to the Ackley 40-degree version does more than just shove the shoulder to a sharper angle. The Remington factory case has a rim measurement of .473 and is .469 just ahead of the rim. The case tapers to .414 at the beginning of the shoulder angle, which is 28 degrees. That's a taper of .055. The Ackley Improved version has less taper. Measurement at the shoulder is .454, which is a .015 and the shoulder angle is a sharp 40 degrees. The improved case will hold more powder, and, as I mentioned earlier, will also reduce case stretching, and this should be of particular interest to varmint hunters who reload their own ammunition.
Nosler's 4 reloading guide shows a maximum load of 40 grains of IMR4895 generates a muzzle velocity of 3,951 fps. I used a load combination of 43.5 grains of H380 powder behind a 50-grain bullet shown in Roy L. Towers' article in the February 1997 issue of Precision Shooting. Towers showed an instrumental velocity of 3,816, which would make true muzzle velocity around 3,846 fps. I got an IV at 12 feet of 3,783 fps. True muzzle velocity would be around 3,808.
One of the main points argued by the 22-250 Ackley Improved crowd is that their cartridge's velocities are comparable to the 220 Swift. I won't dwell on that aspect. From my own point of view, I found the 22-250 Ackley Improved to offer a bit more velocity than the conventional Remington 22-250 cartridge, but, more importantly, it is just as accurate. With its increased velocity, the Ackley Improved 22-250 does offer the varmint hunter top accuracy at ranges beyond the factory 22-250.
Is going the Ackley Improved route worth the time and expense involved• I tend to agree, but that's just one man's opinion. Keep in mind the 22-250 Ackley Improved is not a wildcat; the conventional factory case will fire in the improved chamber, but the case immediately takes the form of the improved chamber,
I don't know what the going rate is for improving a chamber, but it's probably around $100 plus the price of a set of Ackley Improved dies (40-degree shoulder) available from RCBS. I think it's a worthwhile project.
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