Boolit Sizing

[BruMatt]

I have tried to read as much as I can about the relationship of bullet to barrel and chamber throat size in order to begin casting and also "accurize" my 45 Colt. My reading tells me that, if my barrel is .452, then my cylinder throats should be .4525. My cast bullets should be .4518 to .452. These measurements would also work for 45 ACP loads used in the same revolver. Am I reading it right?

When I order molds, should I order to the .452 spec or perhaps .454 and size them down? Is one better than the other? Thanks for the help.

[felix]

The larger the nominal (caliber) boolit diameter, the less damage is done to the boolit by sizing. Simple percentages. So, sizing a 454 boolit to 452 is a nit compared to sizing a 226 boolit to 224 where significant damage can (and is) done when the sizing operation is less than perfect. ... felix

[Outpost75]

The current issue of the CBA Fouling Shot No.223 has an article by Ed Harris on p.10 in which tests of different bullet diameters are conducted in .45 Colt firing an M1909 New Service with .455" cylinder throats and .453" groove diameter and a New Model Ruger with .452" cylinder throats and .4505" groove diameter. The meat of the article is on pages 12-13 and both the narrative and extensive tables of accuracy and velocity results are enlightening. If you haven't yet joined the CBA, having this one article is worth a year's dues by itself!:

"Cylinder throat diameters of the Colt New Service revolver measure .455.” As-cast Saeco bullets fit them optimally without sizing. The accuracy results obtained, despite tiny fixed sights, which are difficult to see well, reflect this. The tighter cylinder gap of the 4-5/8” Ruger revolver (0.006”) produced somewhat higher velocities than the Colt New Service, which has a 5-1/2” barrel, but with a .008” cylinder gap, which is fairly typical of revolvers made before WW1.

Firing .45 Colt ammunition loaded with unsized .455 bullets in the Ruger revolver, having tighter .452 cylinder throats, degraded accuracy, but not enough to seriously impair utility for field shooting. Resizing as-cast bullets from .455” to .452” to fit the Ruger’s cylinder throats improved the accuracy of .45 Colt ammunition. But reducing bullet diameter to fit the cylinder throats, when assembling ammunition in Schofield brass, crimping bullets in their normal crimp groove, at 1.40” OAL, did not. Seating bullets out in Schofield brass, crimping them in the lubricating groove, at 1.55” overall length, improved grouping when bullets were properly sized to fit the cylinder throats, in powder charges adjusted to obtain normal service velocity.

Best accuracy was obtained in the Ruger revolver when bullets were resized from their as-cast diameter of .455 down to .452.” A Lee push-through sizing die was used to obtain proper fit in the Ruger revolver cylinder. Results illustrate the importance of fitting bullets to the cylinder throats, rather than to barrel groove diameter (.4505” in the Ruger vs. .453” for the Colt, respectively). It is best that molds drop bullets at correct diameter, so as to not require sizing."

[44MAG#1]

Just get a mold that is .453 or .454 and size them to the diameter you want. That will allow for different alloy shrinkage and whether you cast with a hot mold or one just barely hot enough to fill out.
An extremely hot mold will cast slightly undersize. Known as shrunken bullet syndrome.
No need to try to make rocket science out of this as it is fairly simple.
Cast with a decent alloy, size and use a good lube and find a good load.
As long as the throats are slightly over groove diameter or the same size, size the bullets just as a slip fit and load away.
There will be many posts on this subject but try the pain free and easy way first.