Anatomy of a Revolver


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gravelyctry
August 28, 2007, 10:22 PM
Just got a Ruger SRH, and I'm trying to pick a bullet to reload 45 Colt. So far, I'm managing to get myself confused by bullet diameters of .451, .452, and .454. I'm pretty sure I'm not going to use the .454 dia., but I'm not sure about the .451 and .452. The many posts in this forum have helped some, but one post in particular suggested that "you need to know your bore diameter, groove diameter and cylinder throat diameter before you choose a bullet size."
Could someone explain what is the bore diameter, the groove diameter, and the cylinder throat diameter, where I measure each of them, and what impact they have on bullet selection? Thanks in advance! Neil

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coelacanth
August 29, 2007, 12:18 AM
from my experience there is a lot to be learned from the various reloading manuals available at nearly any gunshop so I would start there. Cylinder throat diameter is the first thing the bullet encounters after it is fired followed by forcing cone diameter and then the dimensions of the lands and grooves in the barrel so all these are important to accuracy. To accurately measure your chamber throat diameter you can use an inside micrometer but barrel lands and grooves are best measured by "slugging the bore". That is pushing a soft lead slug down the bore and out of the muzzle and then measuring the diameter with a micrometer. The forcing cone on my Ruger Blackhawk is a little loose from the factory ( slightly over the chamber throat diameter but not enough to cause serious accuracy problems ). Depending on the dimensions of your gun and what type of bullets you use .452 or .454 should shoot well but work up your loads in accordance with safety guidelines in your reloading manuals. There is a wealth of info available here on the internet but I favor a good manual on the reloading bench. Try the Handbook of Metallic Cartridge Reloading, or the books by Hodgdon and Speer.

Majic
August 29, 2007, 03:47 PM
Jacketed bullets are forgiving and the .452" bullets will be fine. When dealing with cast bullets should you know the demensions for top accuracy and then the throat diameter will be the controlling factor.

YosemiteSam357
August 29, 2007, 06:24 PM
First, you would be better served posting your question in the Handloading & Reloading (http://www.thehighroad.org/forumdisplay.php?f=15) section of this board.

Next, I'm far from an expert, but here's what I've figured out through reading, since I started loading this caliber: Older Colt (the manufacturer, not the caliber) firearms (real old; pre-WWII, etc) had larger (.454") bores and appropriately sized chamber throats. This is why they still make .45 Colt bullets sized to this larger diameter.

Modern .45 Colt (caliber) guns have .451" or .452" bores and shoot .451" to .452" bullets. Most jacketed bullets I've seen have been .451". Lead are available in both sizes. You must slug your bore to determine it's actual size.

Modern Ruger .45 Colt guns generally have undersized chamber throats (.450") which squeeze the bullet down to below bore size, which negatively affects accuracy, as well as increasing pressure in the chamber. You can have this corrected by many places, but I recommend Cylindersmith.com; The guy that runs that business is a "regular" over on the RugerForum.com site.

Properly sized lead bullets are generally preferred for accuracy sake, but you also have to find the right powder charge for that gun/bullet combination to keep leading to a minimum.

My thinking is that you should never try to use the .454" bullets in a modern .45 Colt unless you know your chambers and bore are oversize. Doing so is just asking for an overpressure situation. (Caveat: Safety is very high on my priority list.)

You need to slug your bore and chambers to find out their exact size. Ideally you will have something close to: .4525" chambers and a .451" bore. You would then use a .451" bullet because that would seat tightly in your .451" bore. You could use a .452" bullet in this situation, but it would cause an (acceptable?) pressure spike. I would not want to use a .454" bullet in this situation.

Slugging will give you a "relief image" of the bore. The bore grooves will cause high point ridges on the slug. Measure across these ridges and you'll have the exact width across the grooves, which is your bore diameter. When measuring the chamber throat diameter obviously there are no grooves.

-- Sam

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