In recent years, I've had the opportunity to work with a variety of high-quality BFR revolvers made by Magnum Research. They have included a 'custom cowboy' .357 Mag., a six-shot .350 Legend hunting handgun and a pair of 'thunder snubs' chambered in rifle calibers. It's been quite the adventure!
But just when I thought the BFR's caliber options had been thoroughly explored by the company and its single-action revolver enthusiasts, we found some fresh ground to plow. This is the story of how the first factory-configured 10mm Magnum three-caliber BFR came together along with its performance results from the shooting range.
Late last year, at the annual NASGW Expo, I had a chance to sit down for a conversation with Mike McNett, CEO and founder of DoubleTap Ammunition. During the conversation, this company's line-up of .45 ACP-pistol-compatible .450 SMC ammunition caught my attention (you can read more about it in this post). But we also spent some time talking about another round that's often overlooked by big-bore revolver fans, namely, the 10mm Magnum.
Don't worry if you just asked, "The 10mm what?" You're in good company. This fairly obscure cartridge was developed as a 'proprietary' round in 1992 by Arcadia Machine and Tool (AMT) as an alternative caliber option for the company's 1911-style AutoMag IV usually chambered in .45 Winchester Magnum. The 10mm Mag. version of the AutoMag IV turned out to be a short-lived offering. With relatively few pistols ordered in 1992, the series was discontinued by 1993.
Time passed and AMT would be purchased by Irwindale Arms Incorporated (IAI), and then later by the High Standard Manufacturing Company. The 10mm Mag. cartridge may have slipped into obscurity if Mike had not teamed up with Starline Brass to revive this round. After looking it over, developing his own loads and putting them through the company’s rigorous in-house testing, this caliber was incorporated it into the DoubleTap ammunition catalog in 2009.
Without any semi-automatic pistols, revolvers or carbines manufactured for this caliber for over three decades, why has DoubleTap kept it in production? Because the 10mm Mag. has a quiet but loyal following among the big-bore wheelgun fans. They have discovered that production double-action and single-action revolvers chambered for 10mm Auto can be converted to fire the more potent 10mm Mag. cartridge with just a little assistance from a qualified gunsmith.
Developed in 1983, the original 10mm Auto cartridge is manufactured today using brass with a nominal case length of 0.992-inches and maximum operational pressure levels of 37,500-psi. When Smith & Wesson compressed the 10mm Auto into the .40 S&W cartridge for the FBI in 1990, they kept most of the cartridge case's external dimensions. However, the case length was shortened to 0.850-inches and the pressure levels reduced to 32,600-psi. These modifications would endear the .40 S&W to law enforcement agencies for the next two decades. But devoted fans of the 10mm Auto would carry on using full-power ammunition as its popularity ebbed and flowed. Today, the 10mm Auto has a stronger following amongst outdoor enthusiasts than ever before, which makes this an ideal time to revisit its most potent variant.
The 10mm Mag. cartridge, as manufactured by DoubleTap ammunition, employs what is essentially a 10mm Auto cartridge case lengthened to 1.290-inches. These rounds are loaded to a maximum operational pressure of 35,000-psi (or 2,500 less than 10mm Auto) and topped with bullets weighing between 135- to 230-grains. The result is a cartridge capable of developing roughly 25- to 30-percent more bullet energy than the 10mm Auto. This moves the 10mm Mag. cartridge's performance potential much closer to that of the .41 Rem. Mag. rimmed revolver round than the 10mm Auto. And it does so while remaining compatible with commonly used 10mm Auto barrel rifling twist rates and well within the pressure tolerances of typical modern revolvers.
The 10mm Mag. cartridge’s case length is the key to its compatibility with the cylinders used to build 10mm Auto revolvers. It is 1.290-inches long, which is the same as, or very close to, that of several U.S. revolver cartridges, including the .357 Mag. (1.290), .41 Rem Mag. (1.290) .44 Mag. (1.285), and .45 Colt (1.285). This means that the cylinders used for those calibers, which are typically used to build 10mm Auto revolvers as well, have enough room front to back to fit the 10mm Mag. cartridge. This includes revolver models like the Magnum Research short-frame BFRs, Ruger's double-action GP100 and single-action Blackhawks along with Smith & Wesson's double-action Model 610 series.
Reviewing the checklist here, most of the off-the-rack 10mm Auto revolvers today are compatible with the 10mm Mag. in regard to their rifling, cylinder lengths and pressure tolerances. All that's required to complete a conversion is a modification to the cylinder’s chambers by a qualified gunsmith. If they have the equipment and know-how to bore the chamber depths from 0.992-inches to 1.290-inches, that’s all there is to it.
After walking through this information with Mike at the trade show, I wondered out loud if the folks at Magnum Research might be willing to build a short-frame BFR revolver based on the six-shot 10mm Auto version they already had in their line-up. I was planning to meet with their team anyway, so Mike kindly offered to walk over to the Magnum Research booth with me, bringing some dummy rounds along with him, to see what we could find out.
We caught up with one of the company's technicians and Mike walked him through the basics of the cartridge and cylinder modifications. The technician said, based on what he could see, there shouldn't be any problem with building a 10mm Mag. BFR as a factory-complete revolver rather than sending out a 10mm Auto to be modified by a third party. But they would need to conduct a bit more research before committing to the project.
Encouraged by this conversation, I checked in with Brett Pikula after the show. He is the production manager for the BFRs and the master gunsmith behind the highly customized Thunder Snub revolvers mentioned earlier. He was on board with the project and correctly predicted that there would be no issues with what turned out to be the first 10mm Mag. BFR they had assembled in-house. Not only did it work out, what may be the first factory assembled 10mm Mag. in over three decades shot very well indeed, as you'll see in the range results.
Among the commonly requested accessories for the BFRs are the caliber-conversion cylinders. For example, a BFR chambered for .45-70 Gov't. can be ordered with additional factory-fitted cylinders chambered in .450 Marlin, .458 SOCOM, or .45-90 Win. But because the BFR is a single-action revolver, the cartridges are head spaced off of the case mouth. This means that the chamber depths have to be cut to match a given cartridge. That’s why, in this case, I requested a second cylinder chambered in 10mm Auto and a third sized for .40 S&W so that I could test all three.
The BFR arrived with an unmarked 10mm Mag. cylinder while the other two are laser engraved with their calibers between two of the chambers. Some folks may worry about chambering the wrong round in a given cylinder. But as you can see in the following photo, there is little chance of this happening. The cartridge case lengths vary enough that, when they are loaded into the incorrect cylinder, the rounds will either drop down too far into the chamber for the firing pin to reach the primer or the rims will protrude far enough out of the chamber so as to prevent the cylinder from rotating or the loading gate from closing.
With three cylinders in the works for this 10mm revolver, much of the gun was kept to the BFR standard configuration. This includes a brushed stainless-steel finish overall, a round-profile barrel, unfluted cylinders, the plowshare grip frame and the standard cylinder pin configuration. The barrel was cut down from 10 inches to a length of 6.5 inches. This barrel length provides a good balance of portability and ammunition performance. It's also the same length as the longer-barrel version of the Smith & Wesson Model 610, which is one of the more popular models to be converted to 10mm Mag. In place of the usual pebbled rubber mono grip, I opted for an upgrade to the smooth, handsome black Micarta cowboy grip panels.
Most BFR revolvers ship with a factory installed, caliber-specific-height front sight paired with a fully adjustable rear sight assembly. But in this case, I made a request for the muzzle to be threaded at 5/8×24 TPI so as to be fitted with various muzzle devices, including muzzle brakes, compensators and, yes, sound suppressors (that's a story for another day). A knurled thread protector was provided. The tradeoff for the threaded muzzle would mean sacrificing the front sight. Since it was my intention to remove the rear sight and install the BFR's aluminum optics rail anyway, I asked for the rail to be installed at the factory. I took advantage of the optics rail to mount a Leupold DeltaPoint Pro with a 2.5-MOA red-dot to the revolver and used it throughout the course of testing.
This BFR’s single-action trigger pull was excellent right out of the box—it was clean, creep-free and breaking crisply with three-pounds of trigger pull. The fitting and craftsmanship was top shelf throughout, as per usual for this revolver series. With '10mm Magnum' engraved on the left side of the frame, this revolver is 12.5-inches long and weighs in at 58.6-ounces, unloaded.
The 10mm Mag. BFR was put through its paces at the shooting range using not only a mix of ammunition grades but calibers as well. The gun proved to be utterly reliable with all of the cylinders and ammunition tested. There were no mechanical issues or ammunition failures. There wasn't even any sticky brass. All of the spent cartridge cases ejected smoothly with light to modest amounts of pressure applied to the ejector rod’s handle.
The formal bench-rested accuracy testing was conducted at 25-yards by firing three 3-shot groups into paper targets. Bullet velocities were measured for 10-shot strings using Garmin’s Xero C1 Pro chronograph. Two loads per caliber were evaluated, one with a relatively lightweight bullet and another with a projectile on the heavier side of the scale. The two .40 S&W loads were manufactured by Federal and Hornady, the 10mm Auto rounds by Underwood Ammo and DoubleTap provided the 10mm Mag.
As expected with a revolver in this size and weight class, the recoil generated by the .40 S&W was tame and easy to manage. This makes it an ideal option for casual plinking, target shooting and some small-game hunting. The 10mm Auto loads had a more moderate kick to them. It was undeniably greater than the .40 S&W but noticeably more comfortable to work with than a lightweight, polymer-framed semi-automatic pistol in the same caliber. The 10mm Mag. moved right up into the stout range with more muzzle flash and noise. But the recoil was by no means punishing by big-bore revolver standards. Instead, it was on par with light to moderate .44 Mag. loads.
As for accuracy results, when working with bench-rested handguns at 25-yards, I look for 3- to 3.5-inch groups when using open sights to indicate that the gun, ammunition and the guy pulling the trigger are operating properly. I can usually shave around a half-inch off of those groups when using the same gun and ammunition along with a micro red-dot optic installed on the frame or slide. I was impressed with the short-frame Custom Cowboy BFR chambered in .357 Mag. when it printed five-shot groups with an average extreme spread of 2.78-inches using the iron sights. For me, those were satisfying results.
So, when I hunkered down with the 10mm Mag. with the Leupold red-dot in place, I would have been perfectly happy to see 3-shot group sizes hovering around 2 to 2.5-inches in size. And that was the case with two of the loads tested. In both of those instances, the 10-shot standard deviations in bullet velocity were in the mid to high 20s. But with the other four loads fired, which held their standard deviation between 7 to 13, the groups were mostly between 1- to 1.5-inches in size. That's some sharp shooting for many handguns and, undoubtedly, a case of the gun outshooting the shooter! Here is the complete set of range results:
Mark Twain said, "There is no such thing as a new idea. We simply take a lot of old ideas and put them into a sort of mental kaleidoscope ..." So too with this first, factory-configured 10mm Mag. BFR revolver. No individual element of this gun is new, and chambering guns in different calibers is anything but revolutionary. However, the way the elements came together was, in this case, oh so satisfying due to the expertise of the revolver’s craftsmen. Not only is this BFR impressively accurate with 10mm Mag. ammunition, it demonstrated the same levels of accuracy potential using 10mm Auto and .40 S&W. In short, this gun exceeded my expectations across the board!
If you have a Magnum Research BFR design you would like to pursue, check out the online custom configuration site here. To see the full line-up of DoubleTap's 10mm Mag. cartridges, including the new SnakeShot load, visit doubletapammo.com. And for those who want to see more of the 10mm Mag. cartridge in action, stay tuned to americanhunter.org for upcoming posts with more evaluations of this cartridge.
Technical Specifications
- Type: single-action revolver
- Caliber: 10mm Magnum with additional 10mm Auto and .40 S&W cylinders
- Cylinder Capacity: six rounds
- Barrel: 6.5-inch round profile; 5/8×24 TPI threaded muzzle; 1:16-inch RH twist
- Trigger: 3-pounds (as tested)
- Sights: none; aluminum optics rail
- Grips: black Miarta
- Metal Finish: brushed stainless steel
- Overall Length: 12.5-inches
- Weight: 58.6-ounces unloaded
- MSRP: $3,309 (as configured); magnumresearchcustoms.com
