.400 Corbon

The .400 Corbon is an automatic pistol cartridge developed by Cor-Bon in 1997. It was created to mimic the ballistics of the powerful 10 mm Auto cartridge by means of a .45 ACP case, necked down to 0.40 in with a 25-degree shoulder.

History and Design
Peter Pi, founder of Cor-Bon and the designer of the cartridge, explained his reason for developing the cartridge: "Velocity is the key to making hollowpoint bullets work. The added velocity assures that the hollowpoint will open up even if plugged with material. This reduces the risk of overpenetration and allows the action of the hollowpoint bullet to dump the available energy into the target."

Mr. Pi said because he wanted the .400 Corbon to be easy for handloaders to make, he based the cartridge on the ubiquitous .45 ACP so that an ample supply of cases were readily available, gave the shoulder a 25-degree angle, and headspaced it on the case shoulder rather than the mouth so that over-all-length is not critical and the bullet can take a tight roll crimp to avoid setback and to get a more efficient powder burn.

The .400 Corbon followed the introduction of the .357 SIG in 1994, which was essentially a copy of the 9mm Action Express without the rebated rim.

Performance
According to Guns & Ammo magazine, Performance is on a par with the 10 mm, yet pressures are much milder. Factory ammo is loaded to +P .45 levels, but the lighter bullet weights make recoil comparable to .45 hardball loads. Felt recoil is a little sharper but still very controllable.

Because of its high velocity for a handgun round, the .400 Corbon offers a flat trajectory, which in turn allows for a greater effective range. Ed Sanow also felt recoil was equivalent to 230 gr hardball in .45 ACP. In addition, the bottleneck case can function better than a straight case with a wider variety of bullet shapes and sizes and allows the use of fully supported barrels.

Ballistics fall somewhere between the .40 S&W and the 10 mm Auto. Unlike the 10 mm which operates at a SAAMI maximum of 37500 psi, the .400 Corbon operates at 29000 psi (although one source states that the pressure is 26500 psi), much closer to the SAAMI maximum pressures for .45 ACP (21000 psi), and .45 ACP +P (23000 psi). Thus the .400 Corbon does not batter converted model 1911 handguns nearly as harshly as the 10 mm Auto, yet performs comparably with up to 180 gr. bullet weights in handloads.

The .400 Corbon is a versatile cartridge useful for target shooting, practical shooting competition, self-defense, and handgun hunting of small and medium game. The loads with the lighter bullets are appropriate for small game. Handloaders have worked up safe loads using 180 gr bullets at 1250 ft/s making it an adequate round for hunting some medium game at close distances.

For practical shooting competitors, the .400 Corbon makes IPSC Major Power Factor of 175 and surpasses the IDPA Enhanced Service Pistol's Power Floor of 125,000 in most loads using a 5 in barrel. The .400 Corbon also surpasses the Steel Challenge Shooting Association's stop plate's Power Factor floor of 120 and qualifies for metallic silhouette Big Bore Competition under IHMSA rules.

According to Ed Sanow, the 135 gr JHP penetrated 9 in of ordnance gelatin and "equals the predicted stopping power of the 10mm 135 gr JHP loads", and that the 165 gr. JHP "penetrates an ideal 12.3 in of gelatin" and "should be a 92-percent stopper, per the Fuller Index".

Ammunition and handloading
Factory made ammunition is available from Cor-Bon in a variety of bullet weights and types: 115 gr Glaser Safety Slugs; 155 gr DPX; 135 gr Pow'RBall; 130 gr, 150 gr and 165 gr tradition JHPs; 165 gr Performance Match.

Many shooters, however, handload their own ammunition to save money. Fired .45 ACP cases can be resized and trimmed to handload .400 Corbon cartridges. New brass cases are manufactured by Starline Brass and are readily available directly from them and major mail order retailers such as MidwayUSA. According to Starline Brass, "The primer pocket was changed from large pistol primer to small pistol/rifle primer in 12/00. Test results concluded no adverse effect from switching to small primer pocket. Cor-Bon is now recommending Win. small pistol works best and if using small rifle Remington 7½ works the best".

Lee Precision, Inc. offers a .400 Corbon 3-Die set. Redding Reloading, according to their catalog, offers custom made 3-die sets for the .400 Corbon. Lubricating of the bottleneck case can be avoided when starting with .400 Corbon cases by using a carbide .45 ACP sizing die before using the .400 Corbon sizing die. Using a 5-stage progressive reloading press makes this less of a chore.

Setback of the bullet in the case—which can cause excessive pressure—can be avoided by using a tight roll crimp and, if necessary, Corbin's Hand Cannelure Tool for jacketed bullets. Since the cartridge headspaces on the shoulder rather than the case mouth, a tight crimp will not cause headspace problems.

Information on handloads for the .400 Corbon can be found online, in fact the standard .45 has two SAAMI standards: 21000 psi for standard loads, and 25000 psi for .45+ loads. The top full-power factory 400 Corbon loads just slightly exceed the .45+ standard. It should be noted that most of the starting 400 Corbon loads with a 5 in barrel still make the IPSC Major Power Factor, even without stressing the caliber's upper limits.

Corbon said that they gave the 400 Corbon to the market and have no patents on this cartridge whatsoever. Eventually, someone with several thousand dollars may even have SAAMI set a standard for it.

Handguns and conversions
Les Baer offers both his Baer 1911 Premier II 5" and Premier II Super-Tac pistols either in .400 Corbon or as a .400 Corbon & .45 ACP dual caliber combination.

Nearly any .45 ACP pistol can be converted to utilize the .400 Cor-Bon cartridge with only a drop-in replacement barrel, and sometimes a heavier recoil spring (for 1911s this is usually an 18 - 20 lbf spring, although a few need a 22 - 24 lbf spring). Suitable recoil springs are easily installed when changing barrels and readily available from many gun parts suppliers, including Wolff Gunsprings. There is no need to buy new magazines or guide rods or change extractors.

Because the .400 Corbon shares the same breechface dimensions as the .45 ACP, modern M1911s can be converted to it without requiring a replacement slide or ejector. Since a .400 Corbon conversion virtually matches the performance of the 10 mm yet does not require purchasing another handgun, some call it the "cheap man's 10 mm". A conversion also retains the versatility of easily converting back to .45 ACP as needed. In this context, Gun & Ammo wrote, The .400 Cor-Bon is one of the more useful of the current crop of .45 ACP offspring. There are faster rounds, but the .400 Cor-Bon is simply easy to get along with. You don't need extra-heavy springs or tricked-out guns for this round -- just drop a .400 Cor-Bon barrel in your favorite .45 and you are good to go.

As of July 4, 2008, the following companies offered .400 Corbon conversion barrels: Clark Custom Guns (drop-in standard and compensated barrels for 1911s); EFK Fire Dragon (1911s, Glocks, Sig P220, HK USP, and the Springfield XD); Fusion Firearms (1911s); Jarvis Inc. (1911s) (Glock); King's Gun Works (1911s); and Les Baer (1911s in National Match grade with 5 to 6 in barrel lengths). Roto 4M (1911 series barrels in 4 in (Commander), 5 and 6 in lengths (Government)). Bar-Sto no longer offers them. Lone Wolf Distributors also offer a drop-in conversion barrel in 400 corbon for the glock 21. StormLake offers drop-in for Glock 21 and Glock 30.