A tale of two Molds

[richbug]

I popped the cherry on 2 new Molds this morning dramatically different results...

The first was a Lee 6 cav 9mm 124 RN, I took it out of the box, attached handles, Bullplated it, smoked it, and started casting. Second batch out of it was perfect, dropped nice bullets all morning. Pleasure to use, dropped 600 nice bullets in no time.

The Second was an RCBS 35-200FN, took it out of the box attached handles, degreased, lubed, and started casting. 10 fills later I started to get something that looked like bullets. 15 fills later the front cavity started making nice filled out bullets. Still haven't got a nice bullet out of the rear cavity. the gas check area just won't fill out. I have cleaned it again several times, the only way to get good fill on the rear cavity is to pressure cast it, then I get whiskers at the vent lines. Why are RCBS Moulds 2x as heavy as need be? That Son of a gun gets heavy fast, and the long handles make it feel even heavier than it is. Any thoughts on it?

Got about 50 decent bullets out of it.

[Glen]

Sounds to me like the upper part of the rear cavity isn't venting properly. Check the vent lines at the cavity and see if there's a burr blocking them. Sometimes the cherry will turn a burr right at the edge and keep the vent lines from working. A dental pick is useful for checking and clearing such burrs.

Second option is that you could take some 600 grit SiC sandpaper and touch up the upper edges of the mould faces, where they join just under the sprue plate. You don't want to remove lots of metal, just round the edges, creating a "vent line" that will fully vent the base of the bullet when the rest of the vent lines are blocked with alloy.

Third option is to loosen your sprue plate slightly.

[richbug]

Third option is to loosen your sprue plate slightly.

You mean RCBS's self loosening sprue plate? That could account for the occasional decent bullet from the rear cavity now.

appreciate the help, checking the vents now.

[stocker]

richbug: You have to crank down on the set screw pretty firmly to make it hold. Also, RCBS puts a small piece of brass between the set screw and the sprue plate screw that will bite into the threads on the sprue screw (say that fast 10 times). Any chance you've lost that brass? If you have you can replace it by cutting a hort section from a small brazing rod.

If it still doesn't hold after tightening the set screw firmly then chances are you have too much tension on the sprue plate screw.