A bit of a drift here--------not much.
I don't have the first clue about which brand of ammo/powder makes for the worst powder fouling. I do have a clue about lead fouling----especially in this case.
Pretty much immediately after I read the terms "686" and "38 Special", my teeth started to hurt. Now just to make sure the cause of my teeth hurting was what I thought it was, I checked. Sure enough---a "686" is chambered for .357 Magnum cartridges. There is no doubt you can fire .38 Special cartridges in a .357 Magnum revolver. They will go bang---they will make a hole. The hole is unlikely to be exactly where it should be, but it's a hole. If "close enough" is okay with you, you can stop reading. Otherwise---------------------
It is an established fact that the longer the throat, the worse the accuracy. The throat for a .38 Special in a Magnum chamber is 1/10" longer than in a .38 Special chamber. That's not much in distance---try it in percentage increase. More to the point-------there's a "shoulder" in a .357 chamber. It sits about that same 1/10" ahead of a .38 Special bullet. I think "shoulder" is the proper term---I think of it as a scraper. It scrapes lead from the .38 Special bullet when it passes---a little or a lot. Two things just happened: The first is you just sent a defective bullet into the barrel-----and then out of the barrel. The second is you just introduced some superfluous lead into the picture. That lead is going to end up on the cylinder face and/or in the barrel---maybe even out of the barrel---if you're lucky. Of course, luck has nothing to do with any of this; because you put that .38 Special round in that Magnum chamber on purpose. You might want to think about that purpose.
I shoot for accuracy---best accuracy. It got to the point where it almost stopped being fun, and started to be work----that quest for accuracy----but it was most certainly enlightening.
It starts with a rest----a machine rest. Call Brownells and get one. They cost next to nothing---compared to a 686---probably less than half.
Get enlightened. Learn how to make holes where you want holes.
Ralph Tremaine
As an aside, and speaking of getting enlightened, get a hold of a custom .38 Special target revolver from the 50's-60's. The cylinder's going to be essentially the same length as the cartridge case. The (wadcutter) bullet is going to sit flush with the end of the cylinder (and obviously the barrel is set back to suit). The throat length is going to be----let's call it ZERO. Test that combination in your rest. Same church, different pew: Sit and stare at a New Model #3 Target revolver (38-44 S&W caliber-------and its cartridge----the first 38-44-------these from the late 1880's). The cartridge case is the same length as the cylinder (the bullet's seated inside---considerably inside). I'm told this combination was/is the most accurate revolver ever made (factory made). I'm told it set records yet to be broken. I never tried to check that claim out. I also never tried to test that revolver/cartridge combination. I have one of those revolvers----and some ammo------but. But I have only two rounds of the ammo----and they cost me $15----each-----20-30 years ago. They're just to look at.
