Reaming .45 Colt Revolver Cylinder Throats

While it is possible that a .45 Colt revolver with cylinder throats measuring from .002 to .003 inches larger than groove diameter (.454 to .455-inch cylinder throats with .452-inch groove diameters) can give acceptable accuracy with the right cast bullet and load, it is also generally accepted that a revolver with sub-caliber cylinder throats will give accuracy referred to as "lousy." If a bullet is undersize in the throat and isn’t soft enough to "slug up" and form a gas seal, hot gas can blow by the bullet eroding the diameter even further causing inaccuracy and leading.

Conversely, if a bullet is oversize for the throat and must be swaged down to less than bore diameter upon firing, the same effects will be noted and pressures can rise dramatically. An undersize cylinder throat can be cured easier than an oversize one. If oversize the only real fix is anew cylinder. If the cylinder specs out undersize a simple reaming job can put the gun in good shooting order, all things being equal. Aye, there’s the rub, as the Bard would say. In guns and shooting all things are rarely equal.

Bullet diameter, hardness, load, etc., can all influence accuracy but the fact remains that an undersized cylinder throat will not allow the gun a fair chance to shoot its best until it’s repaired. A cylinder throat for a modern .45 Colt with a .452 inch barrel groove diameter should ideally measure no more than .4525 inches or, at most, .454-inch. This is .002-inches larger than the bore in diameter.

Some of the older barrels, especially on Colt’s and other revolvers chambered for .45 Colt can run as much as .454inch in groove diameter and even larger. That is why we have commercial cast bullets available in .452 and .454 inch. Unfortunately, many shooters do not understand this concept. One other consideration that would be of interest to shooters of heavy cast bullets such as the various LBT designs is that a small cylinder throat may actually prevent these bullets from chambering.

While doing my research for this article I came across two good references which are revealing. The first was the Speer Manuel for Reloaded Ammunition #7 Copyright 1966. The other was the Lyman Reloading Handbook 44th edition Copyright 1967. A quote from the introduction in the Lyman book,

"We labored long and hard to make this 44th edition the true ‘bible’ of reloading." Another interesting quote from the Speer manual, "Unfortunately, we were able to recommend only one powder for loading the .45 Colt, Hercules Unique. Other powders gave very erratic results in our tests and should not be used." The Lyman book lists six different powders without this caveat and includes one jacketed bullet, a 250 grain half-jacket of unknown manufacture. The rest are cast.

The Speer book, even more interestingly, only references two cast bullets, a 240 grain and 255 grain SWC (semi-wad cutter). Both bullets were sized to .454-inch diameter. Ruger introduced the Blackhawk in 1955 chambered for .357 Magnum. The .45 Colt caliber was not that far behind as was the .44 magnum in 1956. Why almost ten years later do these strange comments appear in the Speer manual?

Hercules 2400 (now Alliant) had been around for many years and has been used in the .45 Colt with much success, although neither one of these references list it as being suitable. Many other powders of the time have been shown to be used satisfactorily. Could it be that instead of mismatched propellants, mismatched cylinder throats and bore diameters on the myriad of .45 Colts produced up to that day were the problem?

Another quote from the Lyman book gives us insight, "Pre-World War II model revolvers have a groove diameter of .454", while post war models usually run around .451". It is wise to slug your barrel and size bullets to as near the exact diameter as possible. Lyman also gave in their Specifications section a bullet diameter of .450" to .454" Nothing is mentioned about the cylinder throat diameters. The latest reference in a major reloading manual is Speer #13, fourth printing November 2001.

They claim that their cast bullets sized to .454" "create a good fit in the chamber throat." How they arrived at this conclusion after noting comments above is perplexing. The loads they list are to be used in Cowboy Action Shooting (CAS) and are borderline squibs. Also, at the short ranges this game is shot, I doubt if any accuracy differences can be noted.

Experiments by Dave Scoville, Editor in Chief of Handloader magazine, produced conclusive evidence of the value of matching the cylinder throat diameter to bore diameter in revolvers using cast bullets. Why were the handloading experts of the day mum on the subject? I think something to do with the hardness of the bullets used may have been the answer, as the "old timers" used a much softer alloy than what is now used by many of the commercial cast bullet sources.

This softer alloy allowed many of the old guns to "slug up" and mask a variety of sins in tolerances, just as in blackpowder days. Since I am semi-retired I have the time and inclination to test-fire various guns I work on to make sure they are going to do what I tell my customer they will, especially with projects like this one where accuracy claims can be different according to the eye of the beholder. I decided to shoot this Ruger with the hand load I was shooting in my own guns. Why not factory loads?

For one thing, most of the factory stuff available in my neighborhood are designated as CAS loads and for these purposes almost useless. Also, high quality .45 Colt loads have risen dramatically in price and I didn’t want to spend that much just for curiosity’s sake. My bullet was a commercially cast flat nose made for the .45 Colt by an outfit called Brass Plus sized to .452" and weighing a nominal 250 grains. To get a better picture of this lead bullet I tested it with my Lee Lead Hardness Tester.

The best I could come up with after several read

ings was a BHN hardness of 19.3, which is pretty darn hard. I didn’t have access to an appropriate mold or I would have included some bullets cast from wheel weights which average out around 12 BHN or so, but I felt this bullet would give me good indications of how changing the cylinder throat specs to match the bore would have an affect on the accuracy of this gun. There was no sense in including any bullet larger than .452" since the cylinder throats were initially smaller than that.

To measure the throats I took a cast bullet with a diameter of .452" and gently tapped it through the throat with a dowel. All six throats were measured in this way. Pin gauges or "hole" gauges, as some call them, could give good results here, but I don’t think they would be any more accurate than slugging and measuring with a caliper. As I had suspected, the throats averaged 0.449". With the older revolvers such as this one these specs are not uncommon.

All the manufacturers today are doing a much better job, but I still check if the warning signs are there. I decided on a load of 9.5 Gr. Unique for the lead bullets, which is a standard load in most references, giving approximately 900 feet per second (fps) at the muzzle for both lead and jacketed bullets, just about the same speed as the original blackpowder loads. For my own reference, I also tried a jacketed load using Hornady’s 250 Gr. XTP hollow point. I trimmed that load to 9.0 Gr. being a cautious soul.

It’s a lot easier to squirt a lead bullet through an undersize hole than a jacketed one. The Ruger Blackhawk is a strong gun, but I wanted to keep pressures reasonable. For the cast bullets I fired three groups of six shots. For the jacketed I fired one group, as I was concerned about pressures with these undersize cylinder throats. Also, I felt if leading was going to be an issue it would show up with three groups. That is why I shot the jacketed bullets first.

All groups were fired at twenty-five yards using a Winchester pistol rest. I admit to having old eyes, but I was able to keep them on the paper. As can be noted in the photos of the groups I used 9-inch paper plates as targets. This has two advantages. One, they only cost about a penny apiece with the right shopping skills, and two, I use a six o’clock hold which gives me an nine-inch bull’s eye that I can reference very well.

After noting the condition of the bore for leading and measuring the group sizes, I used the Manson cylinder throat reamer kit purchased from our friends at Brownells to open up the throats to a nominal 0.4525-inches. This is a fairly simple job. I call it making a hole bigger with precision. The cylinder is removed from the gun and held vertically in a sturdy vise with padding to keep from marring the finish of the cylinder.

This Manson kit comes with reamer pilots to guide the reamer since rarely are all of the cylinder’s diameters exactly the same. The seven pilots range from .4480 to .4510 inch in .0005" increments, a mark of the precision of this kit. Brownells lists the reamer as part #513-000-001. The pilot pack is #513-000-002. The cost is reasonable but such things fluctuate too much to list them here. As all of us "doctors of guns" realize sometimes the diagnosis of a problem is more complicated than the treatment.

If the problems your customer is experiencing make you suspicious, a few simple measurements can be all it takes to cure this ailment. The fact that this kit is commonly available is an indication that undersize cylinder throats are not exactly an uncommon phenomenon and keeping a professional eye open for this condition could bring in

" some overlooked business. Use of the reamer is straight forward. First and foremost, never reverse a reamer. Reversing can dull and chip it and scar the cylinder throat. Use a good cutting oil. I usually just use plain old WD-40 which works as well as anything else I’ve tried, is readily available and not very expensive. Use the appropriate pilot. You should not be taking off much material. Go slow and clean out chips if necessary. Pull the reamer out by turning it normally and giving a gentle upward pull.

When finished you should have a nice, smooth cut. I normally don’t reblue the inside of the cylinder, but help yourself if you think it should be. Here’s the theory. Undersize cylinder throats will cause leading at the breech end of the barrel since hot gas will go by the too-small bullet leaving deposits as it goes. Accuracy will be poor because of the leading and the undersize bullet rattling down the bore.

The hypoth esis: Reaming the cylinder throat to near bore diameter will cure these problems allowing a properly sized bullet to "slug up" stopping gas blow by, reducing leading and increasing accuracy. What this experiment showed. I went back to the range and shot the same amount of groups and compared them with the first batch. The condition of the bore as far as leading was concerned was like the difference between day and night.

Unique does leave a lot of residue, even the new formulation, but a little Hoppe’s No. 9 took it off easily and there was practically no leading underneath. Accuracy was greatly improved as can be seen from the accompanying pictures. So, does this mean we succeeded? Just as John "Hannibal" Smith from The A-Team likes to say, "I love it when a plan comes together." But one must remember that this is one gun, one bullet, one load and one time that all these factors meshed and gave the results we wanted.

Cast bullet shooting in revolvers, as well as other types of guns, is sometimes as much of an art as a science but there are parameters where we can start handed down to us by the old timers and experimenters who came before. They really knew their stuff. Depending on how many pilots may need to be changed due to variances in throat diameters, this job shouldn’t take but one-half hour.

The Cylinder Smith at Cylinder smith.com is advertising the price of this job for one cylinder at thirty dollars plus ten dollars shipping in case you want to recommend their services instead of investing in the reamers yourself. If your customer is having these kinds of problems you may be able to help. Be aware, however, that sometimes it takes a little more TLC than just doing the shop job and sending the customer out on his own with no expertise to back him up. AG