.257 Roberts Ackley Improved Handloads
Date: Sep 14 2021
Many “improved” cartridges, i.e. Ackley Improved (A.I.), seem to be more fanfare than practical. The .257 Roberts A.I. is not among those. By blowing the factory .257 Roberts out to minimize case taper and creating the trademark 40-degree shoulder, the A.I. version gains a worthwhile edge over the original round. Gunsmith and cartridge pioneer P.O. Ackley developed a wide variety of these improved cartridges, nearly universally including a 40-degree shoulder (opposed to the 28-degree shoulder angle of the .257 RCBS Improved) and all displaying a reduction in body taper. Both aspects result in increased powder capacity. The .257 Roberts A.I. holds around 56.6 to 58.5 grains of water beneath a seated bullet, to the .257 Roberts 51.4 to 53.6 grains, all other factors remaining equal.
The .257 Roberts, shooting a 100-grain Nosler Ballistic Tip Hunting bullet and a maximum load of Accurate A-4350 powder, for instance, hits around 2,898 feet per second (fps) (44.5 grains), a maximum +P load (46.5 grains) with the same bullet clocking 3,048 fps (Western Powders Handloading Guide Edition 1). The .257 Roberts A.I. reaches 3,279 fps with a maximum load of 51.5 grains of A-4350 and the 100-grain Nosler. More remarkably, this also provides performance equaling the .25-06 Remington with the same bullet but slightly lighter powder charges. The .257 Roberts A.I. is quite efficient.
Improved cases, like other P.O. Ackley creations, require nothing more than fireforming factory .257 Roberts ammunition, or better, firing light handloads in a .257 Roberts A.I. chamber. Headspace remains equal. When handloading to create fireforming loads, it is generally recommended that a light load of something fairly fast burning, like H-4895, be used, with bullets seated to solidly contact the rifling lands and ensure the case head remains tight to the bolt face to prevent case-web stretch and potential head separation.
The Sporting Arms and Ammunition Manufacturer’s Institute, also known as SAAMI, has not established maximum pressure guidelines for this cartridge, with those providing load data, such as Western Powders, Sierra Bullets and Nosler, generally agreeing to a threshold of around 62,000 psi. Even with that guideline, understand that variations in reamer dimensions have the potential to cause problems with listed maximum loads, especially with weaker actions. Begin with the listed start loads and work towards maximum loads with caution. Note, too, that improved cartridges often fail to accurately reveal pressure signs due to minimum body taper, so keep close tabs on bolt lift and back off when cycling becomes even slightly sticky. Aside from that, handloading dies are easy to come by, case forming is a snap and the cartridge proved straightforward to load, which cannot be said of many other wildcats. Maximum case length is 2.233 inches. Maximum overall loaded length (OAL) generally measures around 2.52 to 2.78 inches, depending on bullet design, though the chamber on the custom test rifle allowed OALs of up to 3.02 inches.
The .257 Roberts A.I. does everything the original .257 Roberts, or even +P loadings will, it just does it a little faster. This includes anything from varmints and predators – after loading 70-grain Sierra BlitzKing, 75-grain Hornady V-MAX, 85-grain Nosler Ballistic Tip Varmint or 87-grain Speer softpoints – to deer and black bear-sized big game with heavier 110- to 120-grain bullets from a variety of makers. The A.I. version does this with less noise and recoil than the .25-06 Remington or .257 Weatherby Magnum.
The test rifle was a heavily customized ’03 Springfield bolt action holding a heavy, unmarked 26-inch barrel measuring .82 inch at the muzzle. The trigger had a bit of creep and broke at 2.80 pounds with some overtravel. The barreled action was bedded in a chunky walnut stock that included a high comb and very wide forearm that made it steady across a rest. It was finished with a Hogue recoil pad. The rifle was topped with a Tasco 6-24x 50mm scope set in Tally rings atop two-piece Weaver bases.
The .257 Roberts A.I. performs best with medium-slow burn powders and a variety of relatively new and classic powders were chosen, including Hodgdon H-4895, Varget and H-4331sc (all temperature-stable Extreme Series powders), Alliant Reloder 15 and 19, IMR-4064, IMR-4831 and IMR-4350, Western Powders Ramshot Hunter and Big Game, Accurate A-4350 and A-2700 and Winchester 760. Bullets consisted of one dedicated varmint bullet and four solid big-game numbers.
The 85-grain Nosler Ballistic Tip Varmint is a firebrand varmint bullet, it’s blue polymer tip and sleek boat-tail design created a .329 G1 BC perfect for longer shots and with construction ensuring dismantling impacts. Paired with Hodgdon H-4831, Varget and Alliant Reloder 15, this bullet averaged .87-inch overall groups. Alliant Reloder 15 performed the best, providing good velocity and the best accuracy, including the best group with this bullet, a .58-inch three-shot cluster. H-4831 and Varget (both temperature-stable Extreme Series powders) broke .75-MOA, the former with 52.5 grains at 3,169 fps, the latter with 43.5 grain sat 3,298 fps. Varget edged Reloder 15 out for top velocities.