i have read a little, and have some basic knowledge of the basics on this subject. that the boolit diameter must be as large as both the barrel, and the throat of the cylinder. i am tinkering with my wife's 38 special. the boolits i am shooting drop at .362", so they are PLENTY big enough. the cylinder throats measure (with a caliper, that is all i have for now) .357", and the barrel slugs out at .358 (again, caliper). i am not sizing the boolits, i am just tumble lubing them and shooting them. i do not load these hot, just something fun to shoot. so far, it has worked out pretty good. but today, i tried a different lube with disastrous results. and i spent hours cleaning the lead out of this little gun. normally after 200-400 rounds, there is a small amount of lead streaking in the barrel. today, it looked like a 747 jumbo jet made of lead landed on a runway. when i was cleaning out the cylinders, i noticed a fair amount of lead at the base of the taper of the throat. i do not usually use a 5x eye loupe when cleaning, so this may be a new phenomenon, or it may be left over. i do not know. that is what started me thinking about this whole deal. what made me think about tinkering is that the machining is quite rough in there. i am thinking i have some room to work with to smooth things out. since the only "J" bullets that get run thru this are a box of P.D. Hornadys that are in it at night. i shot 3 of them to make sure they worked fine, and the rest of the box is untouched. so this is a 99% lead gun. opening things up a little will not effect "J" performance much, as i actually hope we will never shoot them. my brother is a machinist, and thrives on .0001" stuff. the tighter the tolerance the better he likes it. he will be bringing over a .0001" Starrett micrometer and a small hole gauge set to measure this with. i may have him do the work, if he wants to. but i need to know for sure what i need to do. am i right in thinking that the cylinder mouth and the barrel should be the same diameter. or would the mouth being .001" larger be a good thing? that way the boolit would be forced to seal against the barrel wall as it travels.