December 27, 2018
By Layne Simpson
If you have wondered why the 10mm Auto and the 6.8 SPC share the same rim diameter, it is because both are descendants of the .30 Rimless, a cartridge introduced by Remington in 1906 for the company’s Model 1908 semiautomatic rifle. Through the years the 10mm Auto has teetered on the slippery brink of obsolescence, but it now is more popular than ever. A variety of factory ammo along with many new carbines and handguns now chambered for it is proof of its second coming. And while the 10mm is most often thought of as for semiautomatics, it has also been offered in revolvers, the Ruger Super Redhawk and the Ruger GP100 being the latest. But before going there, let’s take a brief look at how the 10mm came to be.
In the 1960s, firearm writers John Adams and Whit Collins, along with barrelmaker Irv Stone and gunsmith John French, decided to give the Browning Hi Power pistol a power boost. The cartridge they came up with was made by shortening the .30 Remington Rimless case to just less than an inch. As was eventually discovered, a 180-grain, 0.40-inch-diameter bullet made by Remington for the .38-40 Winchester could be pushed to 1,200 fps.
The cartridge proved to be a bit much for the Hi Power pistol, so a decision was made to design a new autoloader specifically for it. A prototype similar in design to the Czech-built CZ75 was built by Thomas Dornaus, who was a pistolsmith at Pachmayr Gun Works at the time. Short story even shorter, Dornaus formed a partnership with former police officer Mike Dixon to manufacture the pistol under the name of Dornaus & Dixon. It was Jeff Cooper’s idea to call it the Bren Ten with the acronym “Bren” referencing Brno, the Czechoslovakian arms manufacturer, and Great Britain’s Enfield arsenal. The Bren Ten and 10mm Auto ammunition loaded by Norma were introduced in 1983.
Despite the huge amount of publicity given to the Bren Ten by various shooting publications, Dornaus & Dixon was overwhelmed by financial difficulties and discontinued production in 1986. The cartridge might also have died had Colt not introduced the Delta Elite version of its Model 1911 pistol in 1987. Colt later offered the 10mm in a Gold Cup version of the 1911 as well as the Double Eagle.
Kimber, Ed Brown, Ruger, Rock Island Armory, Les Baer Custom, Nighthawk Custom, Wilson Combat, Springfield Armory, STI, Dan Wesson, and others offer Model 1911 pistols in 10mm today. Other types of autoloaders are also available. A friend of mine has a Glock G20, and another is equally fond of his EAA Witness, which is about as close to the Bren Ten as you will find at an affordable price. And we mustn’t overlook the SIG SAUER P220; it has received a lot of favorable reviews.
The first revolver in 10mm Auto I became aware of was the S&W Model 610 introduced around 1990. Built on the N-Frame, it was available with 5.0- and 6.5-inch barrels. Not many were built, and even fewer of the “improved” version introduced in 1998 were turned out. It had a non-fluted cylinder and was offered in the same barrel lengths as the earlier version as well as a “Distributor Special” with a 3.0-inch barrel. There was also the Model 310 Night Guard with a 2.75-inch barrel; a Scandium frame reduced its weight to 28 ounces. Moon clips were used in those S&W revolvers.
During the year of S&W’s Model 610 introduction, Ruger built a limited number of Blackhawk Convertible single-action revolvers with interchangeable cylinders for the 10mm Auto and .38-40 Winchester. All went to Buckeye Shooters Supply, a Ruger distributor. The revolver’s chambers had headspacing shoulders, and the ejector rod easily punched out fired cases.
As I mentioned, the 10mm Auto is the latest chambering of the large double-action Ruger Super Redhawk. The company also just announced that it is chambering the medium-sized GP100 for the 10mm Auto round. The Super Redhawk, which I used for this report, has a 6.5-inch barrel with a 1:16 twist; it weighs 54.3 ounces on my digital postal scale. A deep crown at the muzzle shelters the rifling from dings in the field.
Sights consist of a fully adjustable leaf with white-outline notch at the rear and a ramped blade with red insert up front. The front sight is attached to the barrel with three large screws. Like other members of the Super Redhawk family, it has an extended frame with scope mounting notches for 1-inch rings. Opposing screws hold the two rings in position while recoil is primarily resisted by the engagement of integral projections on the bottoms of the rings with slots in the top of the receiver.
The Super Redhawk has long been a favored revolver for handgun hunting, and the ever-familiar cushioned grip ranks high among my favorite features. Three stainless-steel moon clips are included with the revolver, but what to do if you arrive in hunting camp only to discover that not a single one made a day-long trip from home? Well, first, that won’t happen if an empty moon clip stays in the gun at all times. Just remember to remove it prior to dry-firing. If opening day of deer season is only minutes away and a moon clip is not on hand, headspacing shoulders in the chambers allow the firing of 10mm Auto ammo without a moon clip. As you can see in the accompanying chart, shooting the revolver without a moon clip had no effect on group size. And since the distance between the primers of cartridges and the firing pin is the same with or without the moon clip, reliability is unaffected. Swinging out the cylinder, holding the gun muzzle up, and smacking the side of the cylinder with the palm of a hand will dislodge some of the fired cases, even when the chambers have become extremely dirty from many firings. A fingernail easily plucks stubborn ones from their chambers. You will have plenty of time for that because thanks to those headspacing shoulders, the deer is down.
A full-moon clip makes reloading a double-action revolver much faster. It also adds to the versatility of the Super Redhawk by allowing the use of shorter .40 S&W ammunition that cannot be used without the moon clip. Why bother? Full-power 10mm Auto loads should be used often enough for practice shooting in order to stay conditioned to the recoil, but they are not needed for all practice sessions. For those who do not handload, .40 S&W factory ammo is a milder and often less expensive option for punching paper. For those who do handload, the .40 S&W can be taken a bit lower in velocity than 10mm Auto, and that results in an even bigger increase in shooter comfort.
I was curious to see how the velocity of the 6.5-inch-barreled Super Redhawk would compare with a semiautomatic with a 6.0-inch barrel. Several years ago I fired the same 10mm loads in a Nighthawk Custom Longslide with a 6.0-inch barrel and a Rock Island Armory Model 1911 FS Tactical with a 5.0-inch barrel. Average velocity difference was 28 fps in favor of the longer barrel. The Nighthawk Custom pistol is no longer with me, so I shot the loads used for this report in the Rock Island 1911 and added 28 fps to what my chronograph indicated for the Rock Island pistol. You can see how those same loads compared to being fired from the 6.5-inch revolver in the accompanying chart. A chambered round displaces about an inch of rifling in an autoloader, and that gives a bullet fired from the revolver a barrel-travel edge of about 2.5 inches. But if a revolver loses some of its push on a bullet due to propellant gas escaping through the barrel/cylinder gap as some believe, there should be very little difference in velocity between the two guns. More on that a bit later.
When .40 S&W factory ammo and reduced-velocity handloads were used, the Super Redhawk was fired over a sandbag rest at 25 yards. But since the 10mm Auto transforms the big revolver into a candidate for use on deer-size game, I extended the range for those loads to 50 yards. All .40 S&W and 10mm loads were accuracy-tested twice in the Super Redhawk. On the first go-round, I used an old scope that had been subjected to several thousand rounds through the years, not only for hunting, but also when checking out the accuracy of various hard-kicking revolvers. Thinking it might be to blame for a flyer in most of the groups, I replaced the scope with a brand-new Nikon Force XR 2.5-8X variable scope with the BDC range-compensating reticle. And since a Wiegand Picatinny mount had arrived several days earlier, it was used with the new scope. As it turned out, accuracy of the Super Redhawk remained about the same. The Rock Island 1911 did not wear a scope, so for shooting it at 50 yards, I mounted it in a Ransom Rest.
Measuring 1.735 inches, the cylinder of the Super Redhawk is quite a bit longer than a 10mm cartridge when it is kept within the SAAMI maximum overall cartridge length of 1.260 inches for the magazines of semiautomatic pistols. A bullet has to free-travel more than an inch prior to engaging the rifling. Bullet jump is even more from the shorter .40 S&W case. I was curious to see if seating the Hornady 200-grain XTP HP farther out of the 10mm Auto case for a reduction in bullet jump would shrink group size. Doing so reduced case tension on a bullet considerably, so in order to compensate, the mouth of a case was roll-crimped into a cannelure applied with a hand tool available from Corbin Mfg. With the center of a cannelure 0.218 inch from the base of the bullet, overall cartridge length was 1.425 inches. As expected, the increase in combustion area reduced velocity, and the loss was regained by a slight increase in powder charge weight. However, there was not enough improvement in accuracy to make the exercise worthwhile.
The revolver wanted to shoot a lot better than my test results indicate. Most groups had four bullets close together with the fifth shot quite a way out. For example, a group fired at 25 yards with Hornady .40 S&W Critical Duty ammo had four shots measuring 0.87 inch, but the fifth shot increased that to 2.85 inches. One of the best groups fired at 50 yards was with the Buffalo Bore Heavy Outdoorsman 10mm load with a 220-grain hard-cast bullet. It measured 2.62 inches for four shots and 3.46 inches for five.
Compared to the Model 1911 adjusted to represent a 6.0-inch barrel, the revolver was faster with all loads. Overall average difference for the 10 test loads was 51 fps, but two loads were 83 fps and 110 fps faster in the revolver.
There was not a big difference in accuracy at 50 yards. Overall, the Model 1911 averaged 5.49 inches, and the Super Redhawk averaged 5.71 inches. When digesting their favored loads, it was 4.65 inches for the pistol and 4.89 inches for the revolver.
The Super Redhawk is also available in .41 Magnum, .44 Magnum, .454 Casull, and .480 Ruger. The 10mm Auto is considerably less powerful than those cartridges, but it is enough for taking feral hogs and deer out to 75 yards or so when an expanding bullet weighing 180 grains or heavier is placed into a vital area. Recoil of the 10mm cartridge is quite a bit less than for the others, and that makes it a likely choice for any hunter who is sensitive to recoil.