Changing Calibers: Revolver Cylinder Reaming

Back in the 1960s and 70s, there was a popular trend to convert large-framed handguns from smaller calibers like .357 Magnum to fire big-bore cartridges such as the venerable .44 Special and .45 Colt. Interest in the .44 Special was initially sparked by Elmer Keith. For years, Keith lauded the performance of the grand old .44 in his book Sixguns and in countless magazine articles.

It was Keith who whetted everyone’s appetite, but it was the articles written by the late Skeeter Skelton, covering caliber conversions he had gunsmiths perform on various revolvers, that really piqued the interest of shooters and experimenters and began the caliber-conversion craze in earnest. You didn’t necessarily need anew cylinder to convert a large-frame revolver from a smaller caliber.

The big N-frame Smith & Wessons, the Ruger Blackhawk, and Colt Single Action Army cylinders are all fairly large in diameter and have enough parent material to allow them to be re-bored to the larger caliber and then re-chambered for the specific cartridge. Once the cylinder chambers are enlarged, dealing with the barrel is a matter of changing the small-caliber barrel for either a factoryor custom-made barrel in the larger caliber.

In some cases, the existing barrel can be bored out and re-rifled to the larger caliber by a barrel maker. Another option is to have the original barrel "lined" to the new caliber. Lining, of course, is where the inside of a barrel bore is drilled out to a much larger diameter, then anew barrel liner is permanently installed into the original barrel shell. This may sound suspect, but when it’s done right, lining can work very well. The U. S.

Navy has used this technique on heavy-caliber rifled barrels for more than a hundred years. Converting a revolver cylinder chamber from a smaller caliber to a larger one is normally at least a twostep process. It doesn’t matter much what the final caliber is, the process used is still basically the same’one of enlarging the holes. In a nutshell, it involves a "size-reaming" first. Sizereaming enlarges the basic diameter of the chamber to the chamber-mouth diameter of the new cartridge.

After On the left is a Clymer .44-caliber finishing reamer, while on the far right is a special-made Clymer cylinder sizereamer with an extra pilot bushing. The Colt SAA cylinder on the left has been converted to .45 S&W Schofield. To its right is a Colt 32- 20 cylinder, and on top is an S&W 32-44 cylinder from the 1880s. size-reaming comes "chamber-reaming," which is where the actual new chamber is cut. Right about now, I know someone

will be asking: "Why do I need expensive reamers? Can’t this job be done with twist-drills of the appropriate size?" The answer is, yes it can and the gun would shoot; but no, this is not the right way to ream a cylinder. Twist drills are designed to simply remove a lot of metal quickly, so the surface finishes produced by drills are normally very rough when compared to the much finer finished holes produced by reamers.

What’s more, the chances of producing six accurately and consistently sized chambers with drills are, to say the least, pretty darned slim. Over the years, I’ve run into lots of older revolvers with chambers that were enlarged by drilling, and every one of these guns gave poor performance. In many of these, the cylinder had been effectively ruined for future use (at least in that caliber), and I’ve seen a few guns that were actually unsafe because the chamber dimensions were so far off.

Here’s an example: A Colt SAA came into the shop a few years ago.

The owner’s complaints ranged from spitting lead, to inaccuracy, to bulging cases on at least two chambers, and three other chambers where the bulged-fired cases would stick and From left to right, the reamers are: cylinder size .357 inch to .430 inch solid pilot, cylinder size .358 inch to .401 inch with pilots, cylinder size .320 inch to .358 inch with pilots, .38 S&W Special finish, 10mm automatic finish, .44 S&W Special finish with pilots. were difficult to extract.

Believe it or not, his biggest complaint was that the revolver ruined his brass, which cracked after only one or two loadings. This old Colt had been converted by a previous owner from 32-20 to .45 Colt. The person who did the work had installed anew factory .45 Colt barrel.

It was readily apparent that a twist drill in a drill press had been used to enlarge the chambers out to about .45 caliber (the outside of the cylinder still showed vise-jaw marks), and the cylinder had been "final chambered" with another drill. A quick look showed that some of the chambers appeared to be closer together than others, especially at the front of the cylinder, an indication that the drill bits were not held in exact alignment with the chamber centers.

When I measured the chamber mouths, instead of .451 to .454 inch, their diameters ranged from .458 to .470 inch. That and the off-center chambers would account for both the spitting of lead and the accuracy complaints. The chambers themselves should have been roughly .480 to .482 inch; instead they ran the gamut from .505 inch down to about .499 inch.

It looked like someone had used a standard 1/ 2-inch drill bit to produce these "chambers," which were not only grossly oversized, but were all different in both length and diameter. Also, the surfaces of the chamber walls were full of deep cut marks and gouges. After looking this gun over carefully, I told the owner that the cylinder was ruined and he was lucky that bulging, cracked, and sticking cases were the only problems he had.

Once the cylinder was replaced with the correct factory part, the revolver performed normally and accuracy was restored. Back to reamers: They cut much slower than drill bits and normally remove less metal, so we can use reamers to produce a fine finish and to bring the hole to an exact size. Because of their design, reamers can remove a very specific amount of material.

Pay attention to the difference in the size and shape of the chips produced by each method and you will see that, where the twist drill quickly tears out strips of material, the reamer slowly "shaves" bits of steel. Yes, this shaving process does take longer than drilling’actually much longer’but it also produces a far smoother surface and greater consistency. This helps to ensure that each chamber is an exact duplicate of the ones on either side.

As to keeping the holes straight, reamers that are designed specifically for this work are piloted. The pilot guides the reamer through the original hole, making it so much easier to stay on center. As I mentioned, the first step in cylinder re-chambering to a larger

caliber is called cylinder "size-reaming." This step is where a special reamer is used to take the chamber from say, .357 inch (.38) caliber to a basic larger caliber, which for arguments sake, we’ll say is .430 inch or .44 caliber. Size-reamers are specially made and are piloted so that they’re guided straight into the chamber. They are also step-tapered to take the smaller caliber out to the larger caliber.

The beautiful cylinder-size reamers shown in this article were special-ordered facturing Co. hester Hills, By its very nature, a sives a lot of metal; however, it is turned and fed slowly with lots of oil and is removed often for cleaning. The next step in re-chambering is the actual "chamber-reaming," where a finish reamer of the appropriate caliber is used to slowly cut anew chamber into the raw .430-inch chamber.

Converting a single-action cylinder, like a Colt or Ruger, involves altering the cylinder chambers only. With its separate extractor, bringing a Smith & Wesson to a larger caliber requires that the extractor star be installed in the cylinder so it is reamed right along with the chambers. Recently, I had some very interesting caliber-change projects in the shop. These involved the conversion of both types of cylinders to some rather unusual calibers.

Here’s how the work was accomplished: Reaming can be done in the lathe or by hand. In the interest of showing the average small shop that this work is within your capabilities, I’m going to illustrate the hand method. I’ve heard some say that the lathe method is faster, although having done this both ways, I strongly doubt it, and in the end, it’s quality rather than speed that we’re after. The cylinder has to be held tightly.

I clamp it firmly in a small bench vise that has its jaws padded with leather to protect the surface against damage. You’ll be using lots of oil, so you want to think about how to mount the cylinder so you don’t end up with a huge mess. I mount the vise at the end of the bench so the cylinder can drain straight down into a five-gallon bucket. (The container should be large enough to hold lots of steel chips, too.) The work is still messy, but this setup helps keep the mess contained.

The oil you use is up to you, but it should be something that is produced specifically as a cutting oil for machine work. Cutting oil not only lubricates cutting edges of your tool, but it helps to move chips out of the way of the tool. I’ve used a product called Brownells Do-Drill in the shop for years with terrific results, and there’s another readily available cutting oil known as Tap-Magic that also works well.

With the cylinder mounted in the vise between padded leather jaws, we’ll start with an appropriate cylinder-size reamer. The reamer shown in the photo has removable pilots, so if we desired, we could enlarge a chamber with a .312-inch mouth (like a .32 S&W) or one with a .320-inch mouth, such as the S&W 32-44 caliber, New Model No. 3 from the 1880s that I’m working on here.

Once reamed all the way out, the cylinder will have straight chambers in .3575-inch size, which is the correct chamber-mouth diameter for the .38 Long Colt I eventually want to end up with. To use the reamer, you need some sort of tool handle. You can use a commercially available tap wrench or your own variation. I made my own many years ago to suit the way I like to use cylinder-chamber reamers. In the photos, you can see my shop-made wrench that was fash-

38 Long Colt. 38 Long Colt chambers produced by the Clymer finish-reamer. ioned from a 3/8-inch square-drive socket extension. I use the female end (the 3/8-inch-square hole) to drive the reamer, and have added a couple of #6-48 set-screws to hold the reamer in the tool. The handles are about 4 inches long, made from 1/4-inch drill rod, with the ends padded with plastic tubing to make it easier on the hands.

You could use longer handles on the wrench, but I find the shorter handles keep me from overdoing it when I am turning the reamer. Always keep in mind that you never want to push too hard or turn too fast when reaming. This is a gentle process. Here I think it’s important to interject a valuable tidbit about reaming’ one that you should never forget. In fact, if you don’t remember anything else from this article, try hard to hold onto this: Never, under any circumstances, try to reverse the direction of a reamer.

As a general rule, reamers are made to cut and turn clockwise. If you turn the reamer backwards, you run the risk of pulling steel chips back under the edges of the tool. This will both scar (as in "ruin") the tool, and will gouge up the beautiful hole you are trying to cut. So, even when you are reversing pressure to remove the reamer from the hole, always turn the tool in the same direction. Also, be gentle and steady as you use the reamer.

Use a light but constant downward pressure applied evenly with both hands. If you encounter resistance, stop. Pull the tool out of the hole and clean everything before proceeding any farther. So let’s get started. Don your safety glasses; you’ll be making thousands of tiny chips, and there is no sense asking for trouble. Insert the reamer with the tap wrench attached into the chamber, and be sure to try to guide the tool to keep it pointing as close to straight down into the hole as possible.

Remember, that pilot isn’t long enough to reach the chamber mouth, so it can’t guide the reamer perfectly straight yet (it will once you have cut down into the old chamber a little way), but for now try to be conscious of keeping the reamer straight. Pour some oil around the reamer and push down lightly as you turn the tap wrench with both hands. I make a habit of turning the handle one-half turn at a time, and I repeat this six times.

At that point, I have turned the reamer three full turns, after which I’ve accumulated a fair amount of shredded steel bits that need to be removed. Remove the tool and use a soft toothbrush to brush all the chips in the reamer into the trash pail. If you have compressed air in your shop, blow the reamer clean. Swab the chamber well with a soft bore brush, being sure to remove any remaining chips. If need be, run a tight cleaning patch through the hole’but get that hole clean.

Reinsert the reamer, squirt some oil down around the flutes, and repeat the process. The work will get a little easier as the reamer enters the chamber far enough for the pilot to engage the chamber throats. When that happens, the pilot will do most of the work to keep the reamer aligned, and you’ll notice the cutting will get smoother and you’ll be cutting more material. This is not brain surgery, but like brain surgery, it takes patience and consistent adherence to the method.

So go slow, use lots of oil, remove the tool frequently to keep the hole and the tool free from chips, and be sure to maintain that slow, light, constant pressure with both hands. Once the chambers have all been size-reamed’in other words, reamed out to the size of the chamber mouths of the final cartridge’we can begin reaming the actual chambers. Our finish chamber reamer also has a pilot at its front end. That pilot should be compatible with the inside diameter of the chambers you have just reamed.

The pilot of this reamer is intended to slip into the .3575-inch holes we just cut into the S&W cylinder. Ream the chambers using exactly the same

44 Russian after de-burring. All it needs now is a good cleaning. methods that you used for size-reaming the cylinder. You simply repeat the process, using lots of oil and remembering to remove the reamer often and keeping everything free of chips. When cutting revolver chambers for rimmed cartridges, you would normally turn the reamer in until the edges of the rim portion of the reamer just "kiss" the rear of the cylinder. Then stop.

This particular job called for .38 Long Colt chambers, which are identical to .38 S&W Special chamthick. The gauge was slipped over the reamer body and up against the rim cutting edge so that when the washer contacted the rear of the cylinder, I knew I had a finished chamber. I also converted some other cylinders while this article was being written. You will notice that one of the cylinders in these photos is a Colt Single Action Army .357 that is being reamed to accept the .44 S&W Russian.

Per the owner’s request, I sizereamed this cylinder to .428 inch, a smaller diameter than the normal .430 inch. This was done by using a series of smaller reamers. Then I cut the final chamber with a Clymer .44 S&W Russian reamer equipped with interchangeable pilots. These chambers were sized specifically to fit a revolvbers, except for being .13-inch shorter in length. To cut these chambers, I used a brand new Clymer .38 Special reamer that I got from Brownells.

To be sure I cut the chamber to the correct depth using this slightly longer reamer, I made up a washer-like stop gauge that was just .130 inch er with a barrel that has a .427-inch groove diameter, which the owner intends to hand-load for. I also altered another S&W cylinder, a 32-44 caliber New Model No. 3 into an obsolete .41 S&W Special. (Yes, Smith & Wesson actually made such a beast for a short time in the 1880s.

Only two original guns are known to exist in this caliber.) The chambers for this unusual caliber were sized-reamed to .401 inch using a size-reamer I had Clymer make for me. I had to get creative with this one; the final chambers were cut using a Clymer 10mmautomatic finishing reamer I obtained from Brownells, and then I finished it off with a series of straight-chucking Industrial Suplville, NY This took the chamb ew thousandths to their final size.

Reaming through a cylinder’s chambers will nearly always leave those chambers with sharp edges, so as a final step on any reaming job, you should carefully de-burr both the front and rear edges of the chambers. Don’t actually chamfer the edges; you just want to gently knock off the burrs. I used a medium-grit Cratex wheel mounted in a rotary tool. The only step that remains at this point is to prepare and blue the cylinder if desired, since after this machine work the chambers will, of course, be bright steel. I