This was how I answered a similar question on another forum:
Q-I am setting up to cast bullets for my Colt Officers Model Special .38 Special. I have slugged the bore, which measures .3545. The ball end chamber on one chamber measured 356, the others .357, so what size should I size the bullets to?
A- ALWAYS size cast bullets to fit the diameter of the barrel forcing cone or revolver cylinder throats. When bullets are sized correctly you should feel resistance in pushing a bullet when inserted from the rear of the chamber and pushing it out the front of the revolver cylinder, but you should be able to do so using hand pressure only. If bullets cannot be readily pushed through by hand, it raises chamber pressure and causes leading in the cylinder. If bullets readily fall through and out the front of the cylinder of their own weight, this causes forcing cone leading and poor accuracy due to asymmetrical bullet case deformation.
If one chamber is tight, and the others are large, the best solution is to lap out or ream the tight chamber to match the others. If you do not want to modify the gun, then mark the tight chamber and don't use it.
If bullets are sized to fit the one tight chamber, they will fit too loosely in the others and shoot loose groups. Bullets which fit properly in five chambers and which fit too tightly in the one tight give you an otherwise "good group" with a flier.
In my 1959 Colt Officers Model Match revolver I use the Saeco #348 double-end, bevel-base wadcutter cast 10 BHN using indoor range backstop scrap. As-cast bullet diameter is .360", which is the same as factory Remington 148-grain HBWCs. I load these as-cast and unsized, lubricating with Rooster jacket full strength in a proportion of 1/3 cup to 1000 bullets, or alternately using a diluted solution of Lee Liquid Alox cut 50-50 with mineral spirits in the same ratio. Both lubes work just as well for target loads, but if you change lubes you must thoroughly clean and dry the barrel and chambers of the cylinder and recondition the bore by wiping with a patch lightly wet with lube, letting it dry, and then wiping with two dry patches.
Double-end wadcutters require heavier charges to shoot well than hollow base types. I load 3.5 grains of Alliant Bullseye with Remington primers for double-end wad-cutters and 3.1-3.2 with factory Remington HBWC bullets. With the Saeco #348 I seat bullets sprue-cut forward, with the beveled base band exposed. I taper crimp using the Lee Factory Crimp Die applying no more crimp than is necessary to completely remove any mouth flare. Excessive crimp damages bullets and enlarges groups.
For serious target work use cases which were originally used for loading factory wadcutter ammunition. Wad-cutter brass has thinner walls with a long cylindrical section which extends all the way to the seated base of the wadcutter bullet, whereas +P and other cases made for JHP service loads are thicker walled and have a faster internal taper intended to increase bullet pull to improve ballistic uniformity with the slower powders used for factory loading jacketed service loads.
If your target revolver has tight chambers, as mine does, so that fired cases expand very little, .360 diameter bullets seat and hold friction tight in fired brass until the shell head on your loading machine moves to the final station in which rounds should be full-length profiled and taper-crimped.
With a close chambered target revolver or autoloader, it is unnecessary to resize brass. By loading as-cast bullets in unsized brass, and profile taper-crimping in this manner, case life is improved, bullet deformation is reduced and bullet pull is more uniform, because the brass work hardens and springs back much less when it is worked only once in profile crimping, versus when being cold worked three times in the usual method of full length resizing, expanding, seating and crimping.
In .38 Super automatics converted to .38 Special wadcutter and having one locking lug remaining on the barrel you can use the standard 16-pound service recoil spring and 3.5 grains of Bullseye with the Saeco #348 DEWC flush seated. In the Colt Gold Cup National Match and S&W Model 52 pistols with are of straight blowback design, load from 2.8 to 3.2 grs. of Bullseye with the Remington factory HBWC bullets, adjusting the charge as necessary for best accuracy. A 14 lb. recoil spring may be necessary for reliable rapid-fire functioning with the 2.8 grain load, whereas the heavier 3.0 to 3.2 grain loads often give better accuracy at 50 yards, but should be used only with the standard 16 pound service recoil spring to reduce wear and tear on the gun.
Standard .38 Special loading dies work brass excessively because their dimensions are intended to resize cases tightly enough to provide a tight bullet fit with jacketed bullets. If you must load sized brass use a .38 S&W Cowboy Expander plug of .358" to reduce bullet base deformation during seating.
But with a target revolver having correct chambers it is unnecessary to resize fired brass. My loading method is to separately de-cap brass, tumble clean, uniform primer pockets, deburr flash holes and hand prime brass so primers are always seated carefully by feel in a clean pocket. I then use the Dillon RL550b for final load assembly to flare case mouths, measure powder, seat bullets and crimp. I use this same simplified process in loading .45 ACP my match ammo as well.
Using the Lee Factory Crimp die sizes the bullet only if needed to ensure that rounds do not exceed SAAMI Maximum cartridge dimensions. It does so by gentle compression f the bullet inside the case instead of reducing it by radically shear in a die. The un-sized, exposed bevel band ahead of the case mouth enables a positive gas seal in revolver cylinder throats. My .38 Special wadcutter reloads average sub 2-inch 5-shot groups at 50 yards in long series of targets. It takes a very good lot of factory wad-cutters to beat this.
