.45 ACP Revolver and Rifle

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.45 ACP Revolver and Rifle

Postby Outpost75 » Sun Sep 13, 2015 10:06 pm

Cross-Posted through the Kind Permission of Ed Harris

Tales from the Back Creek Diary
Revisiting the .45 ACP Revolver and Cowboy Special Brass

Using the .45 ACP cartridge in a revolver makes very good sense. Most ACP fans worship the M1911 pistol and its variants with quasi-religious fervor. I, therefore, am a heretic for preferring it in revolvers. An S&W Hand Ejector, a converted Webley Mk.IV and Ruger convertible single-action are my favorites. For recreational shooting the .45 ACP is simply hard to beat. It is plentiful, familiar, accurate and easy to load.

The .45 ACP was designed for smokeless powder. Its compact case makes efficient use of the available powder space. Its maximum average chamber pressure is 21,000 psi vs. 14,000 for black powder-era revolver cartridges such as the .45 Colt. Higher permissible chamber pressure helps .45 ACP loads burn cleaner and deliver better ballistic uniformity than black powder-era rounds whose voluminous case volumes may cause velocity variations induced by powder position. Easily ignited, fast-burning powders mitigate these effects.

Ballistics of the .45 ACP cartridge are similar, whether fired in a revolver or auto pistol. Hatcher’s Textbook of Pistol and Revolvers (1935) states that 230-grain .45 ACP M1911 Ball ammunition was loaded to 810+/-30 f.p.s. using 4.9 grains of Hercules Bullseye powder. You can assemble rounds today using modern components and Alliant Bullseye powder and get about the same result. Hatcher tested six each of Colt and S&W M1917 .45 revolvers to compare revolver velocities against M1911 pistols. While I didn’t fire as large a sample as Hatcher, the difference between pistol and revolver velocities is insignificant. Revolvers with barrel-cylinder gap exceeding 0.005” lose about 10 fps per 0.001” additional gap above “mean assembly tolerance.” Revolvers having 0.005” gap or less with barrels longer than 4 inches will equal the velocity of an M1911 pistol.

My S&W Military DA .45 with generous 0.008” cylinder gap chronographs 20 fps slower than a 1911 with 5” barrel, but my Ruger 4-5/8” Blackhawk with 0.004” gap averages about 10fps faster than an automatic, as shown in the accompanying table. Current ammunition catalogs and military specifications list 855 +/- 30 f.p.s. for 230-gr. FMJ .45 “hardball,” fired from a test barrel. Steel cased TW55 military ball and Federal 45D, 230-grain JHP personal protection loads I used for velocity standards fell nicely within those stated parameters.

WW2-era pistols and pre-Series 80 Colts “out of the box” don’t feed semi-wad cutters very well. But 230-gr. lead flat-nosed cowboy slugs such as RCBS 45-230CM and Saeco #954, designed for .45 Colt, feed wonderfully in every .45 automatic, old or new, that I’ve tried them in. The flat nose bullet performs well in the field and pokes nice holes in target paper. Overall, the Cowboy bullets are significantly more effective than round-nosed ammo. Most M1911s cycle reliably with as little as 4.2 grains of Bullseye and a 230 grain cast LFN, at 700 f.p.s., but 4.5 grains is more accurate and happens to be the lightest charge which will cycle an M1A1 Thompson SMG reliably, if anyone wants to know. Five grains of Bullseye is the full-charge “hardball equivalent” in terms of both velocity, energy and recoil if those are more important to you than accuracy.

My general-purpose, utility cast lead load for use in any firearm chambered in .45 ACP, is 4.5 grains Bullseye using either the RCBS 45-230CM, or the Saeco #954. This recipe approximates Hatchers 810 +/-30 fps description of the original service load in an M1911 pistol. With it I get 780 fps. from my 5-1/2” S&W Hand Ejector, 817 from my 4-5/8” Ruger and 980 f.p.s. in a converted Marlin lever-action rifle.

The “full charge” of 5 grains of Bullseye gives 814 f.p.s. from the S&W .45 DA Military which has the maximum allowed cylinder gap for a new revolver of 0.008,” vs. 830 from the M1911. It produces a snappy 872 fps from the Ruger single-action and is still relatively quiet, more a stout pop than a crack, being subsonic at 1047 f.p.s. from the converted 22” barrel Marlin 1894 carbine.

The 800 fps Cowboy bullet load can be assembled either in .45 ACP or in .45 Cowboy Special brass. The Cowboy Special is a .45 ACP case draw with a .45 Colt head. It is NOT the same as Auto Rim brass, and that actually turns out to be a “good” thing. Let me tell you why….

The Cowboy Special rim is 0.512” diameter and 0.060” thick, whereas Auto Rim brass has a 0.089” rim which compensates for the absence of the moon clip. Auto Rim brass cannot be used in the Ruger convertible revolver without machining adequate clearance on the rear of the cylinder for it to rotate with the thicker rim. I see no advantage to modifying the Ruger cylinder, so while some people have done so, I don’t recommend it.
Cowboy Special brass functions normally in the Blackhawk .45 ACP convertible cylinder, as intended. It also delivers fine accuracy, which was NOT my experience when firing the Cowboy Special loads from my revolver’s other cylinder having longer .45 Colt chambers! Ammo loaded in .45 Cowboy brass still headspaces on the case mouth, and can be also be used in the S&W .45 DA Hand Ejector, extracting reliably without having to use moon clips. A happy dual-use solution, which changed my opinion of the Cowboy Special brass.

Extensive testing has proven to me that the 4.5 grain charge of Bullseye is more accurate than the more traditional full charge, “hardball-equivalent” 5 grains of Bullseye, so the “.45 ACP/Cowboy Load” is my “go-to” choice for use in big-bore recreational sixguns. When using ACP ammo in full-moon clips, a practiced shooter armed with a .45 ACP double-action revolver gives up almost nothing in rapidity or volume of fire to his M1911-wielding counterpart. Having a handy and quiet “blooping” lever-gun which uses this caliber too is a bonus!

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