Bullet Sizing

Fit To Barrel Or Cylinder?

When it comes to factory ammunition or reloading with jacketed bullets we really have very little choice when it comes to bullet diameter. However, if we cast our own, and consequently size and lubricate the bullets we have molded, we can tailor the diameter of the bullets to suit our particular sixgun.

For example, I have sizing dies for the .44 Special/.44 Magnum running in one-thousandth inch increments from .427″ to .432″ and for the .45 Colt from .450″ to .454″. When I first started making my own bullets one at a time from a single cavity mold and then tapping them through a sizing die using a wooden dowel, I simply used .358″ for .38 Special/.357 Magnum and .454″ for .45 Colt. I never bothered to measure anything on my Ruger and Colt single action sixguns and didn’t have the proper tools anyway.

As I acquired more experience, my operations became more sophisticated. Early on I learned about slugging barrels and barrel size differences in Elmer Keith’s book Sixgun Cartridges and Loads. I accepted what he said as gospel and I spent several years finding the groove diameter of my sixguns by tapping a soft lead slug through the bore and then measuring. That was Keith’s observations going all the way back to the 1930s.

Here is my point. Suppose I carefully slug the barrel of my .45 Colt sixgun and find it to be .451″. I carefully cast, lube, and size my bullets to .451″ and then equally carefully tailor my cartridges. When I shoot these meticulously made .45s through my Colt results are mediocre at best. Why? I did everything right. Well, almost. I carefully measured the groove diameter, however I neglected the cylinder throats, which on further examination by carefully measuring with pin gauges of the proper diameter, I find are a uniform .454″. So what happens when my .451″ bullets hit the front of that chamber? What happens to a bullet when its base is hit with 15,000-20,000 pounds of pressure? It expands. And what does it expand to? The size of the cylinder throat. So the bullet I carefully sized to .451″ is actually much larger when it hits the forcing cone.

Since the bullet is going to be turned from .451″ to .454″ under pressure, wouldn’t it be much better if it was already that size when we hit the switch? If the bullet is undersized it may swell up perfectly or it may not. If it’s already tailor-made to fit the cylinder throat it will enter in perfect alignment with no distortion.

Gotta’ Test ‘Em

Of course, in a perfect world, the cylinder throats will already match the groove diameter. But, unfortunately we do not live in a perfect world. With most .44 Magnum sixguns from Ruger and S&W there probably is not enough difference to matter, and currently produced Ruger .44 Specials are also very uniform. However, down through the years I’ve found Colt .44 Special and .44-40 cylinder throats measuring anywhere from .426″ to .434″. Ruger, S&W and Colt .45 Colt throats have been all over the map, from .449″ to .458″. Currently produced guns are held to much tighter specifications, and barrel groove and cylinder throat dimensions will be much closer to each other.

So which is more important, barrel groove or cylinder throat dimension? There is only one way to find out and that is by experimenting. This is easy, especially when it comes to the Colt Single Action .45. Size some bullets to fit the groove diameter — which is say .451″ — then size some other bullets to fit the chamber throats, which are probably .454″. Load them over equal powder charges and shoot some groups and you’ll know for sure, won’t you?

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