Brownells'  Cylinder Throat Reamer for .45 Revolvers


by Jeff Quinn

photography by Jeff Quinn & Becky Quinn


Revolver accuracy can sometimes be a source of constant aggravation (see Jeff's earlier writing on this subject at Revolver Accuracy). Shooters experiment with various loads and bullet designs trying to achieve groups that donít resemble buckshot from a skeet gun. Some revolvers exhibit good accuracy with little or no effort at all, while others of seemingly the same quality will not shoot a decent group no matter the amount of work and frustration involved. There are many variables in getting a revolver to shoot accurately, and most gun makers do a good job, at least on their hunting guns. With everything that the bullet must endure before leaving the muzzle of a revolver, it is sometimes amazing that they can place a bullet close to the intended target. In this article, I will not attempt to address every element of revolver accuracy, but one particular, and crucial variable: the cylinder throats.

The cylinder throat on a revolver plays an important part in revolver accuracy in a couple of ways. The job of the cylinder throat is to guide the bullet from the cartridge case into the throat of the barrel. Assuming that the barrel and cylinder are properly aligned, the transition from cartridge case to the rifling of the barrel should be a smooth one, with any slight misalignment corrected by the forcing cone of the barrel.

Problems occur that are detrimental to accuracy when the cylinder throats are not sized properly in relation to the groove diameter of the barrel. The cylinder throats should be the same as, or slightly over, the groove diameter. When a throat is too large, the bullet will be "bumped up" upon firing to fill the throat and then squeezed back down upon entering the bore. In my experience, this is not much of a problem with modern guns. The opposite of this condition is when the cylinder throats are undersized, or smaller than the groove diameter of the barrel. In this situation, the bullet is squeezed down upon entering the cylinder throat and then bumped up when entering the barrel to fill the groove diameter. The problem occurs when the bullet, which is now undersize for the barrel, does not bump up to proper diameter. This happens with both hard cast bullets and jacketed bullets, leaving a bullet traveling down the bore without a good seal or proper rifling engagement, resulting in excessive bore leading and imperfect alignment upon leaving the muzzle, and the result at the target is poor accuracy.

It would seem that after over 150 years of revolver manufacture, that those involved in the process would have settled upon a proper diameter for cylinder throats in relation to barrel dimensions, but it just ainít so. Oddly, the problem occurs most often with our oldest centerfire revolver cartridge in common use; the .45 Colt. This cartridge has been with us for almost 130 years, and still guns are being shipped daily with undersize cylinder throats. I have also observed this condition on new revolvers chambered for the .32 Magnum cartridge. I have several sixguns chambered for the .44 Magnum and Special, the .38 Special, and the .357 Magnum, all with properly sized cylinder throats. I have a few older .45 Blackhawks that have perfectly sized throats. I also have some newer .45 Rugers that have cylinder throats that are too small. I have a pair of .45 Ruger Vaqueros that were shipped with a proper bore diameter of .452, with cylinder throat diameters of between .4505 to .451. I like to shoot the excellent Cast Performance gas-checked bullets (see Jeff's article at Cast Performance) in all of my revolvers for their superb quality, power, and accuracy, but in these two Vaqueros not even these fine bullets would shoot accurately.

Brownells gunsmith supply sells a tool to correct the problem of undersize cylinder throats on .45 caliber revolvers. The tool consists of a throat reamer that will open the throats up to .4525, and a pilot bushing to insure proper alignment of the reamer. They also sell a pack of five assorted pilot bushings to allow for perfect alignment in throats of various sizes. The only other item needed, is a T-handle to turn the reamer, such as is used to turn a threaded tap.

For purposes of this article, I started with the aforementioned pair of .45 Vaqueros. These two revolvers are, except for serial number, identical. They were built about a year apart, but dimensions in barrels and cylinders are the same. Both guns were fired at a range of 25 yards with several different loads, varying from light plinking loads, to heavy hunting loads, with cast and jacketed bullets of semi-wadcutter, roundnose, flatnose, and hollow point design. One thing that these two revolvers shared was consistency. All loads tested grouped between three and one-half to four inches, regardless of bullet design or velocity. Point-of-impact varied with bullet weight and velocity, but accuracy was very consistent. It really sucked.

After the initial accuracy tests, the cylinders were removed from both guns, and the throats were reamed as per the instructions provided. The procedure is very simple, and all work is done easily by hand. It basically involves fitting the pilot bushing to the cylinder throat, oiling the tool, and turning the T-handle. Both cylinders were reamed, cleaned and back in the two Vaqueros within 35 minutes. The guns were then again fired for accuracy using the same loads as previously fired. The results were amazing. With plinking loads, the accuracy was improved by about one and one-half inches at 25 yards, grouping into about two and one-half to two and three-quarters inches.

With the heavier bullets, such as the Cast Performance 335 grain gas check and the Hornady 300 grain JHP, accuracy was greatly improved in both revolvers. The guns were still very consistent, but accuracy no longer sucked. Both revolvers now shoot into one and three-quarters inches at 25 yards, and that is with the fixed Vaquero standard sights. That is as good as I can shoot this type of sight. These two Vaqueros were transformed from a couple of great plinking revolvers into a pair of accurate sixguns for hunting or serious shooting.  They are light, handy, and powerful, with the accuracy to reach distant targets with confidence. They are now what they should have been all along. Iím not picking on Ruger here, as they are not alone in this problem, and are building these guns as they think best, but in my experience, the throat diameters need to be increased.

There are untold thousands of good .45 revolvers that could benefit from this simple procedure, with more being made every day. If you have a .45 Colt, .45 ACP, or .45 Auto Rim revolver, shoot it first. If it is accurate, you are blessed. If it is not, the problem could be undersize cylinder throats, and Brownells has the answer. The reamer with the extra pilot bushings costs about a hundred bucks, but will do many cylinders and last forever if used properly. The reamer with only the .448 bushing is $65, but I highly recommend the extra bushings. You can find Brownells on the web at: or call them at: 641-623-4000.  The part number is 513-000-001 for the reamer, and 513-000-002 for the extra pilot bushings.

Jeff Quinn

Ed. Note: these reamers are available for the same price direct from the manufacturer at:

Dave Manson Precision Reamers
8200 Embury Road
Grand Blanc, MI 48439

Boge Quinn

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Click pictures for a larger version

Brownells' cylinder throat reaming tool is a simple and relatively-inexpensive way to solve a common accuracy problem with .45 revolvers: undersize cylinder throats. As tested, the reamer kit consists of the cutting tool and six pilot bushings. A T-handle, commonly seen in tap sets, and oil are the only other items needed.



The reamer tool is easy to use, even for the inexperienced pistolero.



Guns tested for this article were two identical Ruger Vaquero .45s. Prior to testing of the Brownells tool, these two sixguns exhibited great beauty, exceptional handling qualities, and terrible accuracy.



Test loads included some of the author's favorite .45 Colt loads, including the great Cast Performance 335-grain gas checked bullet (3rd from left). These loads have proven to be very accurate in guns with properly-sized cylinder throats.



Prior to testing of the Brownells tool, "Gun #1" (shown at left above) was slightly more accurate (or less inaccurate) than "Gun #2". Gun #1 consistently sprayed groups of about 3-1/2" with any reasonably-accurate load.



Gun #2 was also consistently inaccurate prior to testing of the Brownells tool, producing patterns (one hesitates to call them "groups") of about 3-3/4".



Author bench-testing the test Vaqueros. Jeff's lack of patience with inaccurate revolvers is well-known, and led him to test the Brownells cylinder throat reamer.



Author found the Brownells tool very easy and intuitive to use. Both Vaqueros were completed and reassembled in less than 35 minutes.



Results were amazing, with both guns now capable of consistent accuracy of 1-3/4" at 25 yards, which is as well as the author can shoot with the rudimentary Vaquero sights. For less than a hundred bucks, this tool is a great solution for a common problem with modern .45s and will last forever given proper care. Jeff considers the Brownells cylinder throat reaming tool a necessity for the serious .45 shooter.