All 1911 type guns should not be converted for the Rowland
MAP specification for the .45 ACP, .45 ACP +P, 45 Super and 460 Rowland from various sources are 21,000 PSI, 23,000 PSI, 28,000 PSI, and 40,000 C.U.P respectively. The last unit of measurement is inconsistent with PSI, however, data appearing elsewhere can bring this pressure spec into context. Accurate Arms, the company assisting Clark in developing load data, indicates the cartridge was developed to the 45 Winchester Magnum 40,000 C.U.P. pressure limit, a cartridge with a CIP standard of 39,885 PSI. The maximum loads that serve as the basis for the 460 Rowland cartridge's advertised performance, generate pressure levels below the 40,000 CUP level, more typically the 34,000 ~ 38,000 range. While in sharp increase to the standard 45 ACP, the Rowland is not much different from other current high intensity handgun cartridges for guns of similar design: 40 Super 38,000 PSI, 400 Cor-Bon 33,500 PSI, 357 SIG 40,000 PSI, 38 Super Auto +P 36,500 PSI, 10mm Auto 33,400 PSI, 9mm Luger +P 38,500 PSI, 40 S&W 35,000 PSI.
Clark Custom Guns addresses the increase pressure of the 460 Rowland in several ways, the first by limiting 1911 conversion candidates to only quality firearms. As of this writing, this includes:
Colt Government Model
Colt 1991A1 Government
Colt Gold Cup Government
Colt Gold Cup Commander
Colt Enhanced 1911 Government
Colt Enhanced 1911 Commander
Kimber 1911 Government
Norinco 1911 Government
Springfield Armory 1911-A1 Government
Clark has not developed kits for Glock, Ruger, Sig Sauer, H&K and S&W 45 Semi Auto Pistols, and yet I do not feel distressed over the issue, even though I own some of these. While catalogued 1911 kits may fit, Clark specifically does not recommend attempting conversions on firearms from: Israeli Arms International, Auto Ordnance, Llama, AMT, Charles Daly or "GI" 1911. Concerns noted are inconsistent spot heat treating and soft slide top lugs. Clark had produced a kit for Para Ordnance guns, but they have since discontinued the version citing reliability problems. The 460 Rowland, more than any +P or Super load, taxes the limits of the 1911 design. As a point of reference, the pressure equal of the 460 Rowland, the 45 Winchester Mag, was intended for the heavy gas operated Wildey Mag, a design were operation would be naturally dampened. In order to use the same cartridge in the L.A.R. Grizzly, a more traditional short recoil - locked breech design gun, the manufacturer had to rely on some special steps to assure adequate strength: better grade of raw materials, closer fitting parts, in-house Rockwell testing, process certification, reduced firing pin diameter and more closely matched breech opening, maximum lock up surface and contact, and an increased mass slide. Steps weren't taken to thicken chamber or breech wall thickness, steps were taken to prevent the slide from being beaten into submission, and to prevent primer flow into the breech face. Clark addressed the potential for over zealous slide movement problem by hanging a compensator on all 460 Rowland barrels. The compensator causes a partial pressure drop before the barrel drops and releases the slide, which dampens the slide's movement. The compensator is so effective, the 460 Rowland, with 30% more chamber pressure and 15%~20% more velocity, uses a lower recoil spring rate than a typical 45 Super conversion. The compensator approach even allows for the conversion of the shorter 4.25" barrel Colt Commander.
