Revolver throats play a major role in the accuracy of the weapon. The throat is the part of the cylinder where the actual bullet rests when the chamber is loaded.

Different manufacturers have different specifications for the diameter in this area for any given caliber. Small throat size is not a manufacturing defect. It is intentional, since most shooters buy regular, copper jacketed bullets for their guns. There are also manufacturing tolerances that can play a role, to include variation between the chambers and the throats being too small to properly shoot lead bullets.

This is critical to lead bullet shooters because, with lead bullets, the throat needs to be slightly larger than the actual diameter of the bullet and the groove diameter of the bore itself.

If the throat is smaller than the bullet diameter, it will reduce the diameter of the bullet as it passes through. If this diameter is smaller than the bore (groove) diameter, the bullet will be too small for the bore, causing it to tilt and skid its way down the bore.

Hot gasses from the propellant will also blow by the gap, further reducing accuracy and causing leading as the bullet sheds lead going down the bore. This is especially true with the popular hard cast bullets being used today. Old-style, soft, lead bullets that are under pressure will expand to fill the barrel. Hard cast bullets will not.

For example, if your bullet diameter is .452, which is typical for a lead .45 caliber bullet, the throat should be .4525. The bullet or a round .452 lead ball should be able to be pressed through the throat with finger pressure. This will ensure that the bullet is not disrupted by the throat and will engage the forcing cone and the bore at the proper diameter.

There are several ways to ream your throats. The simplest way is to take your gun to your local gunsmith. It usually costs about $50.

However, you can also do this yourself with a simple tool available form several vendors. We used the tool available from Brownells to ream the throats of five Smith and Wesson .44 magnum revolvers. At $130 for the reamer and the complete pilot bushing pack, it’s clearly a good deal if you have several guns to do or can share the cost with some of your shooting friends.

The tool is very easy to use. You just make sure you have plenty of cutting oil and run the reamer through the chamber from the larger end. The pilot bushing centers the reamer perfectly. Several pilot sizes are available, per caliber, to match the current diameter of throats, for maximum precision. The end result is throats that are identical and the right size.

Our need to ream out the throats was for a slightly different reason. We have tested and found that the Beltmountain Punch bullets are excellent for large and dangerous game protection. The punch bullets are made to .430 diameter and we have found them to average quite close to that figure if not a bit on the high side at times. These bullets have a thick brass jacket that is very hard. In trying to load for this bullet pressure signs appeared well before what we felt a maximum reasonable velocity was achieved. Measuring the cylinder throat on a couple of our Smith and Wesson revolvers revealed a range of 0.4285 to 0.4291. While this is in specification and not a big problem with standard 0.429 copper jacketed bullets we reasoned that is may be a problem with our oversized Punch bullets. Since we only shoot either hardcast lead bullets, or the Punch bullets, loosing potential accuracy with regular jacketed bullets was not a factor for us.

Our thinking was that, upon ignition, the need to swag down the hard, brass jacketed bullet immediately after ignition was causing pressure peaks. After reaming the chambers to 0.431 we found that we could increase our load and gained over 100 fps with no pressure signs. Accuracy with hardcast bullets sized to 0.431 was also improved after the reaming.

After testing on one gun we reamed out the throats on our other revolvers as well as those of some friends. If you only shoot conventional jacketed bullets in your gun, this modification is not needed and may actually decrease accuracy. However, if you shoot a steady diet of hardcast lead bullets or Punch bullets then this is a modification that makes all the difference.