SO, Here it is, got a new to me 686. I've never bartered to slug (pin my cylinders but this time I decided to check them as i got a NTM358311Ideal mold, I have Lyman HI dies in ,357, 358,359.all size .5 tho under stamped dia.I started by trying to push the bullets sized .3565through the cylinder throats, can't push any through with considerable force using a 1/4" dowel. any suggestions on best bullet size. BTW Alloy is CWW+ 2%, thanks Dan.
My first thought on this is a measurement error.
While it’s possible you have a bunch of sizing dies that are under size according to their markings but it’s far more likely the micrometer you are using is off OR there’s an error in the measurement.
I have found S&W throats, particularly the .357 Magnums, to be very close to .357”.
It’s possible you have one that is tight, but it’s also possible there’s an error somewhere else.
Typically, a .356” bullet should just about fall through the cylinder throats. A .3565” should also pass easily. I generally find a .357” – (minus), pin gauge will just pass through a S&W 357 throat, a .357” + will usually go and a .3575” pin gauge will not pass. This is measured over many different cylinders with the pin gauges and cylinders at the same temperature.
SO – Before you start reaming throats and sizing dies, slow down and take a breath.
Regardless of the actual measurements, Size the bullets so that they just pass through the throats with a little resistance – whatever measurement that equates to. Don’t get wrapped around the axle over the numbers. That throat is the last sizing die the bullet will go though before reaching the barrel so it will likely have the final say.
