Question about slugging barrel

[Big Dipper]

I just slugged my first barrel. 357 mag 10" T/C barrel. I measured the lands and grooves with my RCBS calipers. The lands measured .345 and the grooves measured .356. This is my first time so i don't know. After I cast some Lyman 358156 what die do I use in my Lube-a-matic to size them? I am getting closer to shooting some free boolits.

[Kent Fowler]

If you have both a .357 and .358 sizer, then, what ever works for you. If you are going to buy a sizer, I'd opt for the .358 as it can be used to size other 357 revolvers as well.

[mroliver77]

Load a dummy with an as cast boolit and see if it chambers ok. Both my 156 molds drop .358-.359

[wv109323]

Have you verified that your caliper is accurate? I would measure two or three jacketed bullets of known size. With calipers and soft lead in a slug you may be a thou or two undersize If truly .356 I would first try .358 because it is common.

[Big Dipper]

Thanks for the replies. I will verify my calipers with some jwords and also my micrometer. I could not figure how to mic the slug.

[Iron Mike Golf]

Use the micrometer. You don't really need the bore diameter to figure out what sizing die to use. You need to know the groove diameter. Is your barrel rifled with an odd number of grooves? If so, you can tightly wrap a thin feeler gauge around your slug and then subtract twice the gauge thickness.

[Stephen Cohen]

Iron Mike Golf, thanks for that idea on barrels with odd number of grooves, never would have thought of it

[geargnasher]

You're correct, Piedmont, but he isn't measuring a revolver.

My advice is skip the calipers altogether and use the pistol's chamber as a guide, or more particularly, use a cartridge case that was fired with a factory-level load in your gun. Bell the mouth of the case slightly to remove any trace of crimp and use a boolit that is an easy slip-fit into the case. The less slop the resized, loaded case has within the chamber, the more potentially accurate it will be. You can even back the sizer die off until it just sizes the front part of the case to hold the boolit, and leave the rear part fireformed to the chamber. Decap with a punch and shellholder, universal decapper, or something like a .30-06 sizer die if necessary when partial sizing, as some dies don't allow the decapping rod to be lowered sufficiently for this technique. The throat/leade will size the boolit to what the gun likes when fired.

Gear

[Wayne S]

After checking your measuring tool against a known Dia. [J-bullet] Take an as cast bullet, drop it into the chamber. Just for grins take a case as described above, chamber it and close the action. There's a very good chance you will be able the close the action, but also remove the case and the bullet will stay in the chamber.
Now take a wooded dowel,brass rod, something to give the bullet a couple of good tap,then tap the bullet out form the muzzle. Measure the top driving band as that is the only part of the bullet that will have entered the throat of the chamber. That is your sizing Dia. or to the nearest .001 larger. You measure .3575 go .358, you measure .3585 go with a .359 .
99% of all Contender bbl's. have very long throats, and it's near impossible to seat a bullet out far enough to contact the lands so you try for a bullet sized so that it is a push fit into the throat

[cbrick]

My advice is skip the calipers altogether, Gear

The very best made calipers are accurate to plus or minus .001". You need to use a micrometer to achieve the level of accuracy needed.

Rick

[geargnasher]

I either use a mic or a tape measure, unless I need a gauge, then I just fit directly to the part that needs fitting. :grin:

Gear