We load a lot of "Heavy Duty" loads here for the .38 Special for use in Smith and Wesson revolvers rated for such power, such as the Model 20 and 23 as well as "homemade" versions of these guns that started off as N-frame models 27 or 28 and we changed to pass as the .38 Special marked versions. (I think I've even seen one built on a .44 Special adjustable-sight frame, but cannot be sure of this. The top-strap was not checkered but was grooved -- which the 28 is not -- but the top of the frame was "pinched" so it was definitely not a Model 25 or 29 frame. I could not ask the original owner what it had been built out of and the current owner was not a rocket-scientist.)
We often use Green Dot powder for basic "standard practise" Heavy Duty loads. Green Dot (as well as Red and Blue Dot powders) are popular here because powder must arrive in a myriad of ways none of which are above-board. As the original containers are often tossed to the wind, the "dot" identifiers are most helpful to us in determining just what powder we have sitting in front of us in that plastic bag. Of course, 2400 does not have identifiers, but it is a very popular Heavy Duty powder as well because it makes up Elmer's and Skeeter's loadings of the cartridge.
Playing around the other day, I noticed that the powder measure adjustment on my Dillon 650 to throw the standard charge of 7.0 to 7.1 grains of Green Dot for use with the LEE 160 grain SWC (the tumble lube version which we often lube in a Lyman Lubrisizer with RCBS Rifle Lubricant and size to .358) was almost exactly the same as the required setting to throw 13.4 to 13.5 grains of 2400. The required "adjustment" is very small between the two, like about 1/8 of a turn of the adjustment screw.
These are maximum loads, of course, for Heavy Duty or .357 revolvers when loaded into .38 Special casings, and should be approached with caution. Be advised that I am living in Mexico, and any attorney sent to find me had better be Caj or Erich or they won't have much success (and Caj or Erich will probably fall into the Club's Bourbon or Tequila bottle, but they won't be pushed). Work up to the loads and be careful with them should you decide to copy them. Check ALWAYS using a reliable powder scale -- electronic or balance beam, weighing 10 charges instead of just one to get a definite average. Remember that powder has to "settle" to give you a correct reading after being poured into the measure, so take 10 charge readings a couple of times over until it weighs the same two times in a row.
The 7.0 grains of Green Dot loading using the Lee 160 grain SWC gives me about 1,180 fps out of my 4 inch Heavy Duty. The 13.4 grain load of 2400 with the same bullet gives me about 1,310 out of the same revolver. Both loadings offer "one-thumb ejection" in all revolvers we have tried them in, and we have shot several thousand rounds of each loading. It's not "scientific pressure testing" but it will have to do. We are not allowed the .357 Magnum Cartridge down here and it is a ticket to jail to have even one round on you. We paint the primers of all "Heavy Duty" loadings
RED using a permanent marker and all such loadings are carried in
red cartridge boxes to try to help avoid any confusion and/or accidents and I advise that anyone loading .38 Heavy Duty rounds take similar precautions. After all, some schmuck at the range may "lift" one of your rounds off the table to complete his cylinder-load and the results could be undesired if he's shooting an older model .38 Special revolver and not a stronger Heavy Duty rated model.
Play with the loads as you wish and have fun but please be most careful.