Big-Boy Caliber Conversions: The .400 Cor Bon and .460 Rowland

When it comes to versatility, flexibility, and overall usefulness, there are few pistols that can equal the M1911 semi-auto. The design has been around for over 90 years, yet remains at the top of the heap for experimentation and customizing. I sometimes wonder how much farther we can stretch the envelope, but when I see single-shot conversions firing rifle calibers and red-dot sights mounted on the 1911, I realize we haven’t even begun to approach the limitations.

I have extensive experience with the 1911 in the more popular calibers, 9mm, .38 Super, 10mm, and .45 ACP. I have some experience with the .40 caliber, and considerable experience with .22-caliber conversion units. I’ve recently become familiar with two more fascinating calibers available for the handy gunsmith, the .400 Cor Bon and the .460 Rowland. These rounds differ from each other, but the basics of fitting each gun properly are the same.

As for power, the .400 Cor Bon is in the 10mm class, while the .460 Rowland is in the .44 Magnum class—a very powerful cartridge. Often, the conversion goes smoothly, but hang-ups are to be expected. Let’s take a look at each caliber and my experience with various conversions. First, there is rarely any such thing as a "drop-in" part. As we know, slides don’t fit every 1911 frame, and even .22-caliber conversion units aren’t a perfect fit on any old 1911 carcass.

As I’ve discovered when fitting mag wells: All guns are not created equal. We have to err on the side of oversize, because we can’t peen that Smith & Alexander mag well up to fit a pistol, but we can file the frame or the mag well down. But "drop-in" conversions should go better, shouldn’t they? We’ll see. The .400 Cor Bon Conversion With the .400 Cor Bon, all that’s needed to convert the pistol is a barrel.

The one I used was made by Kart Precision Barrel and available from Brownells The .400 Cor Bon is a .45 ACP cartridge case necked down to .40 caliber. There is no difference in the cartridge case rim, so the breechface need not be modified. Barrels are offered in "drop-in" or "gunsmith" fit. The .400 Cor Bon is a hot number, jolting a 135-grain bullet to well over 1,400 fps. This brings considerable momentum to the 1911 slide in comparison to the sedate .45 ACP.

Experienced gunsmiths may remember the .41 Avenger, a .45 ACP case necked down to .41 cal. The .400 Cor Bon is similar, but with a different shoulder, and is much more successful, regardless of the relative merits of the cartridge. When installing the appropriate barrel and expecting perfect function, we are sometimes disappointed. We can have a too-short link that allows the slide to unlock a little early, and the velocity of ejected brass can be excessive.

I have found .290 links usually appropriate for those pistols closest to the Colt 1911 template. Along ejector will most often throw cases out early and damage them. I would not simply fit one out of hand. I’ve found that the standard ejector works fine with the .400 Cor Bon. When the standard part works, it’s all to the good. There is so much to consider in reliability. With the barrel, link, frame, and slide fitted and working in conjunction closely, we have to carefully consider the whole situation.

Slide velocity is increased by a hot round like the .400 Cor Bon. When the slide recoils and returns to battery, with the cartridge pickup rail coming forward to pick up a cartridge, if the cartridge has not yet risen in the magazine we can have a 400 Cor Bon on the left compared to the 10mm cartridge on the right. 460 Rowland. To the immediate left is the .45 Super.

460 Rowland (top) features a nonremovable compensator. Note the deeper chamber compared to the 1911 barrel (bottom). The 460 Rowland barrel fits and functions perfectly in 1911 types. misfeed or tie-up. Or the slide may skip over the cartridge. What we have to do is carefully evaluate the strength of both the recoil spring and the magazine spring. The recoil spring is the first problem. Usually, 18.5-pound springs work fine in the .400 Cor Bon.

However, I worked with one pistol that just didn’t seem to work well with any loading, and .400 Cor Bon ammunition is a little expensive for experimentation. I used a Sprinco recoil-reducing full-length guide rod in this pistol. The secondary or sub-spring assembly inside the stainless-steel guide rod does the business coupled with a WC Wolff premium mainspring, and I have enjoyed excellent function in this Government Model. But that was not all that was required to manage the .400 Cor Bon.

When the pistol was in full recoil, I found that sometimes the nose of the cartridge took a dive out of the ejection port. At other times, the slide would ride over the cartridge and not chamber it. I was using stock Colt magazines, but the problem was evident with practically any magazine I tried. I took a Chip Mc Cormack magazine and fitted it with 11-pound WC Wolff magazine springs. Few of us pay attention to spring rates in magazines, but this was a learning experience.

These magazine springs fight the tendency of the slide to outrun the magazine when hotter cartridges or even +P loads are used in the firearm. I’ve had normally reliable handguns becoming unreliable when subjected to +P+ use. With a heavy recoil spring and matching magazine spring, we have the right combination. The combination I settled on was a Wolff recoil spring of 18.5 pounds and a Wolff magazine spring of 11 pounds.

Still another modification needed to ensure reliability in this weapon was to tweak the feed lips of the magazine. As most of us know, the Wilson Combat magazines feed the cartridge directly into the chamber, more so than earlier styles that usually bounced hardball rounds straight into the feed ramp. Observe a loaded magazine of either type by inserting it into a 1911 frame with no upper assembly mounted. The difference is striking. The other types often butt the bullet across the feed ramp and into the chamber.

This is okay with hardball ammunition, but not with a soft nose hollowpoint. With a properly tweaked magazine and a bit of attention to detail, the bottle-necked .400 Cor Bon will give excellent feed reliability. I find that by opening the last 1/8 inch or so of the magazine carefully, the cartridge is released earlier. This allows the cartridge to pop up early—but not too early—and feed directly into the chamber.

Much of what is done in altering magazine feed lips is by trial and error, with painstakingly small steps. I’ve used several .400 Cor Bon pistols, and the Sprinco-fitted pistol was easily the most reliable. This was after fitting a Sprinco recoil guide, Wolff 18.5-pound recoil spring, an 11-pound Wolff magazine spring, and gently opening the feed lips. If you are going to work with the .400 Cor Bon to any extent, a set of Dillon loading dies will allow you to build affordable ammunition.

The dies are more expensive than comparable loading dies due to the extra effort in building bottle-neck loading dies, but well worth the cost if you choose to experiment with this interesting caliber. Starline offers brass cases, so we do not have to fire expensive factory ammunition to get started. Most .400 Cor Bon conversions proceed flawlessly without any type of problem.

A reader wrote in and asked why I didn’t mention modifying the magazine after I first published an article on the .400 Cor Bon some years ago. I answered that I had not had to work with my magazines. At a later date, I did run into trouble with another handgun. The high-capacity Para-Ordnance, for example, will seldom give any type of trouble due to an excellent magazine design. Finally, never use the .400 Cor Bon in an older spot-heat-treated handgun.

And I certainly would not use it in an inexpensive handgun, or one of suspect origin. The .460 Rowland Conversion Johnny Rowland, the star of a popular outdoors show, invented this cartridge. Much of the credit for the final development goes to Clark Custom Guns This is a semi-auto cartridge with real power, comparable to any load in a four-inch-barrel .44 Magnum. Yet, with proper technique and equipment, the wear, tear, and recoil of the combination is manageable.

Let caution be your guide in loading for this cartridge, as the parameters are experimental.

Still, with concentration and effort, it can be done quickly. 460 Rowland cartridge. It’s tightly fitted to the slide; don’t get your fingers between the slide and compensator during assembly. For safety, the .460 Rowland uses a cartridge case that is .957-inch long versus the nominal .900-inch .45 ACP case. This prevents the .460 Rowland from chambering in a .45 ACP barrel, and also allows the energy of powder combustion to be spread over a larger area. I use Hornady Custom .45 ACP dies in loading the Rowland.

With proper adjustment, they work fine. The .460 feeds in .45 ACP magazines because the overall length of the cartridge is the same as the .45 ACP; bullets are simply seated deeply in the case. The .460 will not chamber in the .45 ACP, and this sets the gun apart from the .45 Super. The Clark Custom .460 Rowland conversion comes with a compensated barrel, 24.5-pound Wolff recoil spring, and a full-length guide rod. Installation is straightforward, but attention to detail is demanded.

Since we’re working with heavily compressed springs, wear safety glasses when dealing with this conversion. The installation steps are as follows: Strip the slide from the frame and disassemble the slide. The barrel, barrel bushing, recoil spring, and spring guide and plug are removed. Now, place the .460 Rowland barrel into the slide. Next, place the new front-spring retainer or plug into position.

Carefully examine the recoil guide and place the buffer end of the twopiece guide rod into the smaller end of the recoil-spring plug. The plug should already be in place in the end of the slide. Now, with the slide firmly in hand, compress the recoil spring by pushing the spring guide and spring into the slide. The cutout portion of the buffer end of the spring guide should be towards the barrel.

Compress the spring until the buffer end of the guide is past the barrel link, and hold it firmly against the underside of the barrel with one thumb. Next, place the slide on the frame far enough to capture the recoil spring, and continue moving the slide to the rear of the frame until the slide stop can be inserted. Rack the slide completely to the rear and lock it in place. Now, install the front half of the full-length guide rod and lock it firmly in place with the supplied Allen wrench.

The slide should never be allowed to run forward by releasing the slide lock; due to the heavy spring, ease the slide forward to avoid the risk of excessive battering. Clark recommends installation of a heavy-duty firing pin to prevent slam fires. This was accomplished quickly and easily by dropping the firing pin stop and installing the spring. Johnny Rowland and Jim Clark are to be commended for clear, easily followed instructions. I took no special precautions in readying the handgun for its first shots.

I liberally doused the long bearing surfaces of the pistol with Birchwood Casey gun oil and loaded my magazines with .460 Rowland ammunition from the sole supplier, Georgia Arms. This is top-quality ammunition that always performs well in any caliber. As I always do in a function test, I readied myself with adequate ear and eye protection. Function was fine, and I have to admit that recoil was not as wild as I had presumed.

Firing offhand, the recoil of the "defense" load, a 185-grain JHP at 1,400 fps, was in hard-ball territory. The 1,550-fps 185-grain load recoiled in .45 +P territory. As anyone who shoots competition realizes, an efficient compensator really does the business. There were no problems in this conversion, so I have no fixes to report. However, I started with a quality gun. I’ve used the .460 conversion in both Springfield and High Standard pistols with excellent results.

Starting with a poor quality gun might have brought problems related to the gun. At this point, I’ve put about 300 trouble-free rounds through the conversion. With full-power .460 Rowland loads using 230-grain bullets, recoil is comparable to the .45 Super, but in the .44 Magnum class. Overall, this is a conversion that works smoothly. Still, if any problems are encountered, I think that the measures outlined above in dealing with the .400 Cor Bon would solve them.

These are both interesting and effective calibers that are sure to become more popular with time. Be prepared, and remember each 1911 can be a case in itself. ■