Ok, I'm throwing this out to get a little education. I'm collecting components together to start reloading for .38 spl/.357 mag. I got some bullets in the other day (148 grn SWC). I pulled out my model 60 and dropped a SWC in a chamber. I did it just to see what would happen (curiosity). The bullet "stopped" before exiting the chamber (front of the cylinder). Now, in my little brain, the chamber is a constant diameter from one end of the cylinder to the other. So, I now know that the chamber does change diameter. Can some one explain why? Thanks.

Ideally you would like to be able to push the bullet through the cylinder throats for a snug fit but without having to use too much force. You want bore diameter to be a bit smaller. I guess in a perfect world you'd want .358" cylinder throats and a .357" bore. You want the dimensions to get tighter as the bullet nears the muzzle so that the gasses are properly contained.

Isn't it amazing how in this day and age of such advanced technology and manufacturing methods that the revolver makers can not/will not give us proper cylinder throat and bore dimensions?

Dave Sinko

Yes, it does change diameter. Look inside and you should see a slight "step" at about the point the front of the case reaches when you load a round. This is what prevents a .357 round from being chambered in a .38, for example, or a .44 magnum in a ..44 Special. A properly-sized bullet should stop as you describe when dropped in, and then you should be able to push it on through with light pressure from behind with something like a dowel or a pencil.

In a revolver, the bullet must make a pretty long jump from the case mouth, through the chamber mouth, across the barrle-cylinder gap and in to the barrel. It is gradually "funnelled" in to the bore by the chamber mouth and then the forcing cone on the rear end of the barrel. Ideally, the chamber mouth should be very close to bore diameter, no more than very slightly oversized, to help accomplish the task while keeping the bullet properly aligned.

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Pisgah

To make up for the absence of the case. Once the bullet leaves the case and travels through the throat it has a smaller diameter than when it was seated inside the case, so the throat is smaller to keep the bullet straight and to keep the gases sealed behind the bullet.

Thanks for the input folks.

There was a time, long ago (in the early black-powder cartridge era) when many rim-fire and center-fire revolver cartridges used a "heeled" bullet (much like the .22 Long Rifle) where the base of the bullet was of a smaller diameter than the 'body' of the bullet, and the 'body' of the bullet was the same outside diameter as the case body. The outside of the bullet would therefore have to be lubricated, which was not ideal, as the 'outside lubricated' bullets could pick up all kind of debris, which would stick to outside of the bullet. Modern center-fire cartridges changed to a design where the case was larger in diameter than the bullet, and the bullet would have a consistent diameter and be 'inside-lubricated' to fit completely within the case. That required that revolver chambers had a 'throat' at the end of each chamber at, or just over, the bullet diameter, to keep the bullet concentric to the bore and funnel it to the forcing cone of the barrel. Any large discrepancy between the diameter of the chamber throats and the bore diameter has a negative, sometimes disastrous affect on accuracy in a revolver. Smith and Wesson, in modern guns and in most calibers, has a nearly ideal combination of chamber throats either right at bore diameter, or .001" over, which usually results in excellent inherent accuracy.