When I took these .45 Colts out to test for accuracy, etc., they produced about the same velocity with a selection of factory loads and handloads. Accuracy, out to 50 and 100 yards, was about the same, although the Ruger seemed to have a slight edge. Oddly, groups with the Ruger spread vertically, while the Colt spread was largely horizontal.
One of the most interesting results to come out of those tests with the 12- and 14.25-inch barrels is that the shorter barrel, along with the more generous chamber and throat dimensions, produced just about the same velocities as the longer barrel with the less generous chamber dimensions. Not that two handguns make a valid test, but thats the way this comparison worked out.
Then too, there are other factors to consider.
On the other hand, we might expect the harder commercial cast bullets (BHN 16 to 24) would create higher pressures when they enter the forcing cone, and thus higher velocities, but they also facilitate the loss of some gas pressure when they fail to obturate upon entering the chamber throat - mitigating the pressure factors by allowing gas to leak by the side of the bullet before it enters the barrel.
Then there is the effect of reloading dies. Back in 1980 I decided the major problem with the .45 Colt was reloading dies that were designed for .454- to .455-inch bullets but were used with .451/.452-inch cast or jacketed bullets. In short, the case mouth wasnt reduced enough to gain a secure hold on the bullet regardless of crimp strength. This particularly applied to loads using slower-burning pistol powders like 2400, H-110 and IMR-4227.
In the summer of 1981, I called Bill Keyes at RCBS, explained the problem and asked if he could build a proper set of dies, to form a longer case neck and include a .448-inch neck expander for use with cast or jacketed bullets sized to .451/.452 inch. I still have the dies Bill forwarded in August 1981, and RCBS .45 Colt dies were changed accordingly shortly thereafter.
In general, using a Colt SAA with a 4.75-inch barrel, the new dies resulted in an average velocity increase of around 100 fps across the board. Slower-burning powder benefited most; faster-burning powders, not so much. The largest velocity increase went to 20 grains of H-110 with the Lyman 454424 SWC cast from a mixture of wheelweights and Linotype and sized .454 inch. With the old RCBS dies that produced a short case neck and .4525 inside neck diameter, the Colt averaged about 880 fps. The new dies that formed a longer case neck and .4485 inside neck diameter boosted that to 980 fps. Both loads used the Federal 150 Large Pistol primer.
Of interest here is that until recently, Speer (up through manual number 11) and other outfits published load data that was developed with reloading dies that produced a .451 inside neck diameter, producing almost zero bullet pull when used with bullets that measure .451/.452 inch.
So, if you have an older set of reloading dies for any cartridge, not just the older numbers like the .45 Colt or .44 Special, check the diameter of the neck expander. The resultant inside neck diameter should be about .003 to .004 inch smaller than the jacketed or hard cast bullet you are using, or about .002 inch smaller than bullets cast from softer alloys - BHN 5 to 11. And make sure the case neck holds the full length of the bullet shank, to ensure maximum bullet pull for optimum efficiency with slower-burning pistol powders.
You can also tear a page out of the old Super Vel bag of tricks and use a jacketed bullet that is about .001 to .0015 inch smaller than standard for the cartridge of interest and get increased velocity with acceptable pressures Ð and good accuracy. At least the Super Vel loads I used over the years shot fine.
There is one other item you might want to pay attention to. All .357- and .44-caliber handgun bullets are designed to place the cannelure in the proper position for the correct overall loaded length for .357 and .44 Magnums, respectively. They are also designed to deal with the higher pressures produced by the magnums. So, they wont obturate when fired at responsible pressures in the .38 and .44 Specials, or the .44 WCF, for that matter. As a result, gas blow-by (when it passes through the chamber throat) with these bullets is critical and, at least in some part, explains why they produce lower velocities in revolvers than bullets that are designed for lower pressures.
So when loading these magnum revolver bullets, unless their diameter exactly matches or slightly exceeds the chamber throat diameter, gas loss will result in lower velocities. Mitigating factors would include the diameter of the chamber throat, chamber diameter and the angle of the forcing cone.
The only way I know to eliminate the problems associated with factory .38 and .44 bullets (and hard commercial cast bullets) is to cast your own bullets of a proper alloy to ensure they form a proper gas seal before they leave the cylinder throat. Its also significant that cast bullets always produce higher velocities than their jacketed counterparts of similar weight. Thats mostly because they produce less friction, but when cast properly, they also form a positive gas seal, harnessing propellant gases more efficiently.
So, it appears that any given handgun may or may not produce velocities that jive with those listed in whatever manual. Moreover, its impossible to predict - without the aid of a chronograph - exactly how much velocity loss or gain will occur with any given barrel length compared to barrels of different lengths. That is, a 4-inch barrel just might equal velocities produced by a 5-inch tube or a slow 6-inch barrel.
Neither does it makes much sense to agonize over 50 fps one way or another in hunting loads. What you get is what you get. No animal will know the difference if your bullets are 75 fps or so slower than you expect. And, they wont necessarily hit the ground deader if your bullets are 100 fps faster than Speer or another outfit suggests. Either way, its little more than potluck.