“Top Ten”

The 10mm Is Perhaps The Finest
Iteration Of The “.40 Concept”

By John Taffin

The roots of the 10mm go all the way back to the last quarter of the 19th Century when Winchester necked down the .44 WCF (Winchester Centerfire) to .40 and called it the .38 WCF. The .38 WCF is more commonly known now as the .38-40 which adds to the confusion as it is not a .38 but actually a .40. The .38-40 was the third most popular chambering found in the Colt Single Action Army. Fast-forward to the 1930’s and we find wildcatters using the .38-40 Colt SAA with new cylinders chambered in such cartridges as Pop Eimer’s .400 Eimer and Gordon Boser’s .401 Special respectively. Both of these cartridges, as did the .38-40, used bullets measuring 0.400-inch or 10mm in metric.

In the 1970’s we have the modern version of the 10mm beginning with a wildcat cartridge known as the .40 G&A. This cartridge used .224 Weatherby brass cut to the proper length and 180-grain .38-40 jacketed bullets which were at the time available from Winchester. Velocities were right at 1,250 feet per second and the cartridge was chambered in a Browning Hi-Power. I gotta believe this cartridge put a lot of strain on the Browning!

In 1984 Jeff Cooper—a staunch advocate of the .45 Government Model 1911—put his stamp of approval on a new semi-automatic pistol and cartridge from Dornaus & Dixon. This double-action semi-automatic could be carried cocked-and-locked, and was basically a CZ-75 9mm with a larger hole in the barrel—a 10mm one. Cooper gave it the catchy name of the Bren Ten. There was a lot of interest in the Bren Ten, however, financial and production problems surfaced. Some of those who got pistols could not get the magazines. By 1987 the Bren Ten was gone and Dornaus & Dixon declared bankruptcy. That could’ve been the end of the 10mm.

The 10mm followed a path parallel to the .41 Magnum sixgun cartridge. Both of these were originally conceived as self-defense/LE cartridges and both proved to be too powerful for such use by mere mortals. However, both cartridges are excellent outdoor cartridges. That is, cartridges used for hunting or for just a very comfortable feeling when carried on the hip as you go off the beaten path.


Today, 10mm semi-automatic 1911’s include (from top right clockwise) the
Colt Delta Elite, Nighthawk Long slide and Kimber Stainless Target II.

The Bren Ten wasn’t the end of the 10mm as Colt came to the rescue by chambering their 1911 Government Model in 10mm, known as the Delta Elite. The original loading for the 10mm, was a 200-grain bullet at 1,200 fps. At the time I believed this was too powerful for continued use in the 1911 and I still do. I will not normally put such loads, whether factory or handloads, through the Delta Elite. If I want 1,200 fps I drop down to a 180- or 170-grain bullet. If I desire a 200-grain bullet, I reduce the muzzle velocity to right at 1,100 fps. Perhaps I am being overly cautious. However, I prefer to err on the side of caution.

Most reloading manuals publish an overall cartridge length for each cartridge. This usually works—but not always. With my first handloads for the 10mm I made the mistake of loading 500 10mm cartridges using both jacketed and cast bullets before I had guns in hand. Definitely a mistake! Since that time more than 30 years ago I have cautioned everyone not to load cartridges until they have a sixgun or semi-automatic to try a few dummy cartridges in for size. Those first 500 reloads following the “recommended” OAL would not fit in the magazines of a pair of Delta Elites.

Since they were not roll-crimped I could use a hand press to seat each one slightly deeper to fit. They now worked perfectly through the magazines of the Colts, but even so adjusted would not fit in the magazine of an IAI Javelina. The lesson is, of course, always, and I do mean always, check cartridges for fit before loading a large batch.

Colt rescued the 10mm and other manufacturers soon followed. Smith & Wesson came up with the excellent Model 1006 semi-automatic while Ruger’s contribution was a Convertible Blackhawk with two cylinders chambered in .38-40 and 10mm. Today, in addition to Colt, such companies as Dan Wesson, Kimber, Nighthawk, and SIG SAUER offer excellent 10mm semi-automatics.

Since the very beginning I have been using both the RCBS and Lyman carbide reloading dies with excellent results. The latter is a 4-die set which makes it especially appealing for use on a progressive reloader with the seating and taper crimping operation separate.


The Kimber Stainless Target II has excellent adjustable sights and
helped make these targets.


The SIG SAUER P220 is the most recent 10mm available and an excellent
shooter as these targets attest.


The extra sight radius provided by the Nighthawk Longslide 10mm delivers
excellent results downrange

Even before I could find jacketed bullets to use in the 10mm, I simply had to reach into my storage of cast bullets for the .38-40 to find three excellent examples. Two of these are the typical roundnose flatpoints which feed well through the Winchester Model 1892. These are Lyman’s 40143 and 40188. Later models of these molds have Lyman’s standard 6-digit numbers 401043 and 401088. Both of these are in the 170-grain weight categories. From Oregon Trail I find their 175-grain semi-wadcutter also works well.

Earlier, I mentioned Gordon Boser. Boser was a dedicated sixgunner and gunsmith who designed a semi-wadcutter/Keith-style bullet for use in the .38-40 as well as his .401 Boser Special. This bullet is Lyman 401452 with a hardcast weight of approximately 200 grains. For general everyday use in the 10mm, this is my cast bullet of preference and with 10.5 grains of AA7 clocks out just over 1,100 fps in a Kimber 5-inch 1911. In my Ruger 10mm Blackhawk with the barrel cut back to 4-3/4 inches and set with a tight barrel/cylinder gap, the muzzle velocity increases to just under 1,150 fps. The weight of the all-steel Blackhawk really dampens the recoil of this load.

I also favor the RCBS 10-200 SWC hardcast bullet which as the number implies weighs out right at 200 grains. This bullet has long been a favorite loaded over 5.5 grains of WW 231 for muzzle velocities of right at 1,045 and 1,065 fps in the above-mentioned Kimber and Ruger Blackhawk 10mms. This load is exceptionally accurate in the Kimber with 5-shot groups at 20 yards grouping in 1-inch. This same load under the Oregon Trail 175 SWC clocks out at just over a most pleasant-shooting 1,000 fps and is also very accurate with groups just over an inch.

Switching to jacketed bullets reveals excellent performance with the 10mm in the SIG SAUER P220 with 5-shot groups as small as an inch up to 1-1/4 inches at 20 yards.


Colt rescued the 10mm from oblivion by chambering it in their 1911 Delta Elite.
The cartridge was too good to die and handloading brings out the best it has to offer.

With the longer sight radius of the 6-inch Nighthawk Longslide I find it easy to get even tighter groups. Five-shot groups of 1 inch or even smaller are not unusual at 20 yards.

The argument continues over whether or not some cartridges are more inherently accurate than others. It is easy to conclude all cartridges would be equally accurate when used in properly toleranced sixguns or semi-automatics with the right size bullet and powder charge. However, generally speaking I have found it much easier to come up with accurate loads for the 10mm than for the 9mm. Guns or cartridges? I simply do not know.

Is the 10mm a hunting pistol? I would place it between the .357 Magnum and the .41 Magnum and closer to the latter than the former. The qualifiers are proper ammunition, discretion as to distance and, most assuredly, bullet placement.



Read More Handloading Articles


Purchase A Password To Read The February 2017 Digital Edition
(Includes FREE Download Of PDF Version For Your Desktop Or Mobile Device)

Purchase a printed copy of the February 2017 issue

Purchase a PDF download of the February 2017 issue now!

Leave a Reply

Your email address will not be published. Required fields are marked *

(Spamcheck Enabled)