Bob,
I did some bullet comparisons for you however remember to take this as food for thought. My studies are far from scientific and only from what I learn from the Lyman's book and what I have for fodder for bullet comparisons. The case length on a .38 special is supposed to be 1.155. I took some empty casings I had and measured them and they varied from 1.137 - 1.145. These were expended rounds. I then pulled apart a .38 special I had on hand. Casing length was 1.145 and the bullet was a 158 grn. lead single flange (ring) round. Seating depth of the bullet was approx. .435. The bullet had the rubber ring on it which I suppose is the gas ring. I could be wrong as I don't reload .38/.357 or at least it has been a long time since I have. The expended casings varied in length from 1.137 - 1.148. That variance is quite a bit. Max COAL for a .38 loaded round is 1.550. I do not know which powder you are using, nor the bullet, and seating depth. Since the .38/.357 is a straight casing, not like a tapered .45, it leads me to believe that, when the bullet is chambered, then fired that some gases are held in the chamber. The amount of gases depends on seating depth, bullet size, bullet configuration and powder used. A hot powder with a shorter bullet will expend the gases in the chamber thus leaving "soot" in the chamber and around the cylinder. I did not load the .38 specials myself, they were given to me by my brother so I don't know what powder he used. So in that context you would have a lot
of "empty" space for the gases to remain in the cylinder. According to Lyman's the best accuracy powders for vary according to the bullet used. For example a 125JHP uses Bullseye 3.2grn starting to 4.4 max. A 158grn JHP flies best using Unique 3.7 starting to 5.0 max. In summation I can only say that bullet sizing and powder are the 2 most contributing factors for having dirty casing and pistol when done shooting. I have shot about 200 rounds that my brother gave me and it was dirty after approx. 50 rounds. I am certainly no reloading expert by any means and the info I have given you is what I believe to be the closest idea of what is happening. Anyone who has more info, I would be happy to jump in on this conversation, and should I be wrong, I would greatfully appreciate their guidance. All ideas and suggestions would be greatly appreciated!!!
Tommy
I had to re-write this topic twice as I had some of my dimensions wrong. I wrote it and thought about it and after a couple of hours realized my mistake. If you had read this earlier, please disregard the former info. I do NOT encourage anyone to use this as verbatim, this was my findings only and recommend that you fact check yourself prior to loading. My wish is that this is a guideline and don't want anyone to suffer any injury.