Bore Size vs. Boolit Diameter Question...

[Foto Joe]

I've read it a thousands times, "slug your bore." But....

And I've probably missed it so don't beat on me too much. What is the appropriate over-size for the boolit to be?? I slugged the barrel of one of my SAA's yesterday and it came out at .449, the chamber throats are .453's. I now have the knowledge (at least on the SAA) but what do I do with it?

[Piedmont]

Revolvers are different. Size to match your cylinder throats and don't worry about what the barrel measures. It (internal barrel size) really only matters when the barrel is larger than the cylinder throats.

[gray wolf]

Sounds like you have a 45 colt, it also seems your barrel if slugged correctly is a tad small and your throats are a tad big. .001 -- to .003 over barrel groove is OK as long as rounds chamber. I like to size to the cylinder throats, in your case that would be .004 over bore. In my case I get the best accuracy with bullets that are a tad snug in the throat. However this will be and is disputed by some. If .453 will chamber and not increase pressure that's what I would go with.
Many things effect what we do, I am sure you will get some good advise from others here. If you go with the traditional .001 over barrel size that would give a fairly loose fit in the throats, it could lead up the throats and probably would diminish accuracy as compared to a snug fit in the cylinder throats.
.449 is small for a 45 colt, seems like .451 is what I would be looking for with
.453 throats.

[ShooterAZ]

In my case I get the best accuracy with bullets that are a tad snug in the throat. However this will be and is disputed by some.

No dispute from me on this one. Sometimes you just have to experiment a little to get it just right. If the boolits just drop right through the cylinder, they are too small IMHO. I try to size them snug, to where they will still push through with some resistance. I use a pencil eraser to push them. The barrel will ultimately do the "correct" sizing after that.

[MtGun44]

Use a .0001" micrometer for this measurement, not a caliper. If you
are using a caliper, you are +/-0.001 accuracy at best, can't really
draw any conclusions if you are using a caliper.

Bill

[runfiverun]

I would have shot the thing already.
I found long ago not to look for a problem until you see one.

[Outpost75]

The current issue No.223 of the CBA's Fouling Shot on pages 10-14 has a detailed article by Ed Harris which shows a couple good illustrations of this in two .45 Colt revolvers, an M1909 Colt New Service with .455" throats and .453" groove diameter and a New Model Ruger with .452 throats and .4505" groove diameter.

While sizing bullets to .454" showed no benefit in either revolver, compared to loading and firing bullets unsized at .455", the .455" bullets showed about a 20% increase in extreme spread in the Ruger, 2-1/2" at 25 yards, compared to 2" or less when sizing the bullets as much as 0.003" down to .452" to fit the tighter cylinder throats.

Firing bullets sized .452" in the Colt New Service enlarged group sizes to over 4" at 25 yards, compared to 2-1/4" for as-cast and unsized at .455", which fit the cylinder throats properly.

He also fired most of the loads in an H&R CR45LC Classic Carbine at 50 yards, and despite the rifle's .452" groove diameter, best accuracy, under 2" at 50 yards, was with unsized .455" bullets, because the barrel forcing cone ahead of the chamber cast .457"!

All the tests were done with Saeco cowboy bullets cast of soft alloy, with Alliant Bullseye powder and Lee Liquid Alox lube. Velocity and accuracy data is given for starting through maximum loads in bolt .45 Colt and Schofield brass, and Harris evaluates the effect of seating bullets out longer in the Schofield brass, vs. normal seating or shooting the same charges in .45 Colt brass. Lots of work!

If you aren't yet a member of the CBA, one meaty tech article like this with multiple tables of accuracy and velocity data you can review, is worth the whole year's subscription. You sure don't see this type of thing in any of the newstand magazines which merely publish puff pieces for their advertisers.

[mdi]

Revolvers are different. Size to match your cylinder throats and don't worry about what the barrel measures. It (internal barrel size) really only matters when the barrel is larger than the cylinder throats.

Yessir! It wouldn't help for the bullets to be larger than cylinder throat diameter 'cause the throats would swage the bullets down as they passed through. And unless your barrel's groove diameter is larger than the throat diameters, you'll be fine sizing to same size as throat diameters...