Sprue Plate Pour Hole Daimeter?

[Doughty]

I would appreciate anybody's thoughts on what the proper diameter of the pour hole should be. Does one size fit all? Should it vary as a percentage of bullet diameter, or cavity volume, or thickness of sprue plate, or what? Why?

[BABore]

Dan, at Mnt molds, recommends a large sprue plate and dipper hole when using WW alloy. especially when pouring larger bullets. I've followed his advise and found it works. A larger SPH solved the fillout problems in a Lee 475-325 mold.

Here's what Dan posted in response to my question;

"The pour orifice on RCBS ladles is about 1/8". That's pretty small, plus it will get partially plugged with dross in use unless you flux religiously. If you have access to numbered drills, a #21 is about the perfect size for all around use. You might want to start out small and gradually work your way up one drill size at a time, because the larger orifice increases flow dramatically, and at first it seems difficult to control. After a while, you get used to it.

My molds will be equipped with the proper size sprue hole, about a #14."

[44man]

I pre-drill my plates with a no. 17 and by the time I cut the taper to a sharp edge, it is a little larger. A no. 14 sounds about right. Works on all boolits from .38 up.

[montana_charlie]

I pre-drill my plates with a no. 17 and by the time I cut the taper to a sharp edge, it is a little larger.
What do you cut that taper with?
CM

[BABore]

I use a 90 degree, multi flut chamfering tool in a hand chuck. Takes a bit to cut them, but you don't push a burr like you do in a drill press or mill. If you must do it powered I have done the following;

Stone the underside of the plate perfectly flat.
Clamp it to a flat aluminum plate.
Drill out the sprue hole to just under the desire size going well into the aluminum.
Set up the chamfering tool and cut until the plate/aluminum interface is a perfect smooth joint (no step).
Unclamp the plate and stone the bottom to remove any burrs.

You need to use a sharp chamfering tool and only a little pressure, take your time.