Cylinder throat questions S&W 625

[rockrat]

Finally took it out today for the first time. Went to the indoor range and proceeded to shoot some cast thru it. Got some leading with the commericial stuff I loaded.

Before it started leading, the thing seemed to shoot, except for a couple of chambers. I could shoot chamber 1 & 2 and just have a bit bigger hole in the target. #3 would be about an inch low. #4 back near the holes from the first two. #5 would be between #1,2 & 4 and #3. Last shot would be about 2" high. Got it home to clean and pulled out electronic caliper to make some measurements and one chamber mouth was .452 (#6) and #3 would be between .4505 and .451 (display went back and forth). All the others show .451.

Thinking the larger chamber mouth lowered pressure a bit and lower velocity, and #3 was just the opposite. Tighter cylinder mouth, higher pressure, more velocity and shot a little lower.

Is my thinking correct? Would it be a good idea to get a reamer and open them up to match the .452 cylinder mouth? Thanks

[454PB]

What is the bore diameter? What diameter were the commercial boolits?

In general, if the throats are undersized, they size down the boolit before it enters the barrel. Assuming your caliper measurements are correct, you may be pushing .450" boolits into a .452" bore. That's a combination that produces leading and inaccuracy.

[Dale53]

Not to be overly critical here, but using a caliber to measure cylinder throats is NOT the way to do it. Remove the cylinder from the revolver, support it properly and drive a lead slug through each throat. THEN, measure carefully with a good, properly calibrated micrometer (NOT a set of calipers). You have to be careful when measuring. A soft lead slug is easy to mash a bit when measuring with a micrometer. If you have little experience in this area, maybe you have a machinist friend who can do it for you. It is REAL easy to be off a couple of thousandths when trying to measure these slugs.

If, after slugging, you cylinder DOES have varying throats, then I would let someone with experience handle this for you:

http://www.cylindersmith.com/

THEN you will have an awesomely accurate revolver with good cast bullets, sized to fit the throats.

Good luck!
Dale53

[454PB]

That's why I worded it the way I did, Dale. I agree, slugging the throats is the more accurate way to measure them.

[cbrick]

Absolutely, no way possible to measure a round hole with flat faced calipers, at least not accurately.

Also it's probable that your commercial cast boolits are too hard for your load/pressure/velocity. This in itself can cause leading and adding Dales scenario that the throats are possibly smaller than the groove diameter and leading is guaranteed not to mention accuracy.

Rick

[Dale53]

454PB;
You know, Elmer Keith in his first little blue book "Sixgun Cartridges and Loads" suggested that the bullet should be a push fit in the throat. If you have some bullets sized close to the needed cylinder throat dimension, you can simply push them through. He suggested that (in a clean cylinder, of course) that you should be able to push the bullets through with nothing more substantial than a pencil. As a for instance - if your bullet sized .452" will not push through but a .451" bullet will, you have your answer (use the .451" bullet:mrgreen:).

Just a thought...

Dale53