One of the problems with revolvers is their inherent lack of accuracy. They’re not highly fitted wadguns. In many of the DR matches I’ve attended, from observing various participants, accuracy can be radically different from one gun to the next—even the same model. Elmer Keith, the granddaddy of wheelgun shooting, wrote at great length about the need to tune all revolvers delivered from the factory. The problem is not with the gun’s design but as a result of poor quality control. It doesn’t matter if you own a classic K-38, Colt Python or a Ruger GP100, doing a little accuracy tuning will easily increase your scores.

This may sound simplistic but you need to have the correct bullet size for any chance of accuracy out to the long line. When cast bullets are used they should be sized for an additional .0005 to .001” larger than the barrel’s groove. The weapon’s owner, with great care, should slug the barrel to determine the actual inside diameter.
There’s a huge difference in slugging a 1911 pistol barrel as opposed to a revolver. Revolver barrels are not readily removable and they can’t be slugged from the base. Yes, they have to be slugged by going into the crown. After removing the cylinder and yoke take a padded mat and place a lead bullet facing up, guide the bullet into the crown then gently apply force straight down on the mat until the bullet is flush. While holding the barrel firmly take a 7 inch long wooden dowel and lightly apply pressure until the bullet has entered the barrel by about an inch. From here on out you can take a hammer or maul and ever so slightly tap the bullet through the remaining distance.
As you tap the bullet make certain your pistol is held firmly in your hand and that any sudden forces aren’t restrained by an immovable object, like a table top. Try to use your arm much like a shock absorber. Most first-timers are generally surprised at how little force it takes to push one through the tube.
Pull out the calipers (although a good micrometer is far more accurate) and you’re done. Having an accurate bullet dimension is critical for general accuracy.
Cylinder throats can be another problematic area. It’s not uncommon to have different size throats in each cylinder. Ideally throats should be about .0010 of an inch larger than the bullet being used. If a throat is too large the projectile will want to cant on its way to the forcing cone and will slam into it off center and shave off portions of the bullet.
If throats are too small, the bullet becomes resized (compressed) long before it reaches the forcing cone. A resized bullet like this traveling down the barrel will never make good contact with the lands. Obviously accuracy will be lost.
If cylinder throats are too large, buy a larger sized bullet. If they’re too small (which is generally the case), chamber reaming or honing is about the only way to address the problem.
Brownells has a pretty nifty tool for chamber reaming. It’s probably one of the few things a person of moderate skill can accomplish on their own without the assistance of a smith. In most cases dramatic accuracy improvements are gained buy having all the chambers being the same size. A T-handle and about twenty minutes with a little care and this little tool will correct a host of ills, assuming you’ve properly cleaned and removed all the lead from the chamber in advance.
About the only other method of achieving great revolver accuracy is by utilizing in-line boring. Not for the faint of heart and for those with money to burn, it’s clearly the most deliberate way of dealing with inherent chamber alignment and sizing problems. But it’s a process best left to well skilled professionals.
Forcing cones have been known to be poorly shaped at the factory. Not because they weren’t properly cut; it’s not uncommon for a factory worker to over tighten the barrel during installation thereby slightly crushing the threads, and in the process, ever so slightly change the size of the opening and angle.
An 11 degree angle of pitch for a forcing cone is generally considered appropriate for proper functioning.
We all know how important a well shaped crown is required for exceptional accuracy. With wheelguns, they need to be parallel with the face of the forcing cone. Recutting the crown and the forcing cone at the same time while the barrel is in the frame is a common cure for maintaining bullet uniformity.
Once you’ve determined the optimum bullet diameter and have adjusted the chambers for consistent size, test your weapon out to the long line. A general rule of thumb is if you can get the revolver to group less than 4 inches at 50 yards—you’re doing great. Remember, these things were never designed to have the accuracy of a free pistol. If your results appear to be disappointing consider talking with a well known wheelgun smith.