.400 Cor Bon: The Little 10mm That Could, But Didn’t

The introduction of the 10mm Auto gave magnum power to the 1911 platform, but as the Colt Delta Elite demonstrated it just wasn’t up to the task. Heavy-bullet loads with their high pressure and recoil caused cracking of the frames and rails. The platform can be beefed up to handle it, but stock guns? The best you can hope for is a seriously curtailed service life.

In 1997 Peter Pi, the founder of Cor Bon, designed a 10mm that would avoid these issues and with light-bullet loads would equal the 10mm’s power. His reason for doing so was that hollow-point bullets require velocity to expand, and bottle-necked cartridges tend to feed well in semi-automatic pistols.

To make a long story short, it worked. Mostly. Both cartridges can comfortably push a 135gr. bullet to 1450fps. for 630 ft./lbs., or a 155gr. bullet to 1250 fps. for 538 ft./lbs. of energy. But as the bullet weights increase .400 Cor Bon lags behind. It’s a matter of pressure; .400 Cor Bon has a lower maximum pressure than 10mm Auto, and you run up against that limit trying to push heavier bullets to 10mm velocities. Many experts in the field say 165gr bullets are pretty much the limit for high-performance loads in this cartridge. People have run 180gr. loads, but these resemble .40 S&W more than 10mm.

People have reported varying degrees of success using drop-in barrels in 1911s, and if you plan to shoot a lot a heavier recoil spring might be a good idea. I’ve read several reposts of people tearing up their 1911s firing this cartridge, but when I looked into these cases the symptoms were exactly what I’d expect from an improperly-fitted barrel in a .45-caliber 1911, so this is hardly conclusive. If you are not intimately familiar with the platform fitting any replacement barrel is probably best done by a professional.

A few guns have been produced in this cartridge, but for the most part it has been an aftermarket modification for 1911-pattern guns. The 135gr bullets have significant authority when used on small game, and the heavier bullets have been used successfully on medium-sized game at limited ranges.

AMT’s double-action backup, famous for it’s brutal recoil, was offered in .400 Cor Bon. That must have been, uh, ‘exciting’ to fire!

Cor Bon, Underwood and others still produce .400 Cor Bon ammunition, but by and large it is viewed as an answer for a question no one asked.

Why .400 Cor Bon?

So, what attracted me to this cartridge? Mostly the fact that I was going through Pinto’s Guns discount section and there was a set of reloading dies for $10. I thought, ‘Hell, why not?’

I played around with it a bit, and forming brass is dead simple; run .45 ACP brass into the resizing die and .400 CB brass emerges. I had the best results by inserting the shell-holder in the ram, running it all the way up and screwing the die in until it made contact with the shell-holder. I had a few 10mm bullets on-hand, so I looked up load data and made up some cartridges. 155gr. JHPs at 1250 fps. making 538 ft./lbs. at the muzzle seemed a good place to start.

I looked up replacement barrels, which are not unduly expensive, and filed it as a ‘to do’ and forgot about it for several months. Recently I remembered and ordered a barrel from SARCO for about $60. It claims to be ‘drop-in,’ and while early barrels from them were poorly reviewed it was generally agreed that they had largely rectified those issues. For the price I decided to take a chance on it.

My 1911a1 Donor Gun, a Frankengun assembled from a Sytema Colt lower and a GI Surplus upper. A dear friend assembled it years ago and eventually gave it to me as a gift. It’s always been reliable, accurate and an excellent shooter.

When it arrived it actually looked better than their picture on the web-site. It came without a link, so I removed the one from the gun’s current .45 ACP barrel and used that as a starting point. I hesitantly re-assembled the gun and checked the fit…

OK, understand this: when my eyes see ‘drop-in’ my brain sees ‘gunsmithing required.’ So I was quite surprised when the barrel fit and appeared to function perfectly. Huh. OK, that bent my reality a bit but I was willing to roll with it. Tentatively. I took it to Champion Arms with the ten rounds I had on-hand and…

It worked. Flawlessly. Perceived recoil was similar to .45 ACP, accuracy was fine and when I took the gun home and disassembled it everything looked… fine. OK then. Bob Rogers sent me some 155gr. TMC-FP bullets and Jim Bensinger sent me some Gold Dot hollow-points. I loaded these over 8.0gr. of Unique with a CCI 300 primer and headed back to the range.

Shooting it

At the range I discovered some interesting things, not the least of which was that the magazines I had brought suck. These are something I’ve had lying around and have been meaning to try out, and because I’m an idiot I thought it would be a good idea to test them and the ammo at the same time. They weren’t catastrophically bad, but the first round out sometimes nose-dived and they don’t lock the slide open.

OK, two different bullets, same weight, similar profiles, same load. You’d expect them to perform similarly, right? You must be new here…

Accuracy was, uh, ‘sub-optimal.’

Starting with the 155gr. TMC-FP I discovered, to my dismay, I was having trouble producing a respectable group at seven yards. I tried some rapid-fire and got these results:

Not at all a good 7-yard rapid-fire group.

OK, Normally I would blame me, but the eagle-eyed among you may have noticed something…

OK, that’s not right…

Yep, about half the bullets are yawing badly, and there’s a couple of full keyholes. This caused immediate paranoia; it hadn’t happened on my first test. Had something gone wrong?

Five shots in five seconds with the Gold Dot bullets , everything went just fine.

Nope, not with the gun anyway. Five shots in five seconds with the 155gr. Gold Dots went just fine. Not sure what’s happening, but the TMC bullets do not like this load.

Shooting this round is not at all unpleasant. Recoil is notably snappier than .45 ACP, but recovery time between shots is unaffected, and further efforts produced similar results. So with the right bullet and load it seems to work a treat. Powerful, easy to shoot and should have a nice flat trajectory.

Reloading

There’s plenty of load-data for jacketed bullets, and I didn’t really find any for cast bullets. I’ll be working on that…

Reloading .400 Cor Bon isn’t all that tricky. Since the cartridge headspaces on the shoulder trimming the brass isn’t a major concern. Care must be taken with the seating die so as not to crush the shoulder. The case can also balloon slightly when the bullet is seated. The SARCO barrel’s chamber is tight, so I’ve found running the loaded rounds into the resizing die (with the de-capping pin removed, obviously) solves any issue with getting the first round out of the magazine to go into battery. Aside from that, though, reloading is a doddle, and the rounds feed very well out of a good magazine.

.400 CB’s Place in the World

It’s not unreasonable to ask, “OK, why?” Damned if I know. Self-defense? The cartridge’s extra power is unlikely to have a profound effect on ‘stopping power’ over other service cartridges. Hunting? The lack of the ability to get serious velocity out of heavy bullets seriously limits the cartridge in that regard. Competition? Under current rules it holds no advantage over existing cartridges like .40 S&W, which can fit more rounds in the magazine. Small-game hunting? Ought to be grand, but again not better than existing, more readily available options.

Honestly, it just doesn’t stand head-and-shoulders above other, more common calibers in any respect. .357 and 10mm Auto can both use bullets with higher-sectional density which ought to give them an edge in penetration, making them more suited to big game hunting or dangerous game defense. Lighter calibers work fine on small game.

Yes, it ought to be as good as anything out there for self-defense, but there are more practical choices available. Still, it works and I’m having fun, so I guess that’s reason enough.

I’ll be doing chronograph and ballistics testing soon, and we’ll see what’s what. Stay tuned…

Be safe and take care.

Michael Tinker Pearce, 31 May 2021

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