Poor Sprue Cut-Off factors from RCBS Cast Bullet Manual

[ohland]

During today's genuflection before the Plumbous Calf, I tripped over this:

Now, a reading from the Book of Armaments...

Extracted from “RCBS Cast Bullet Manual, Number 1”, RCBS, CCI, and Speer Research Staffs, Omark Industries, Lewiston, ID, 83501 Dec 1986. ISBN# 0-935632-07-7 ( hard Bound ) or ISBN# 0-935632-08-5 ( soft bound )

Page 22
"If the sprue is not cut off level with the bullet base, it can impair gas check seating. It may cause problems with plain base bullets while lubricating in a sizer/lubricator by allowing lubricant between the bullet and base punch. A raised sprue cut-off is the result of a loose sprue plate, a bent sprue plate, debris between the mould and sprue plate, or a dull cutting edge. A dull cutting edge can also cause the sprue to break off rather than being sheared, which sometimes leaves a shallow hole in the bullet base."

NOTE: I have had the sprue stick out and torn sprue. Rather tear a little from the base because trimming the extended sprue slows sizing / lubing down...

[Petrol & Powder]

Brother Maynard, bring up the Holy Hand Grenade......

Consult the book of armaments !

[bhn22]

Cabin fever, huh?

Break your sprues by hand. Breaking sprues with a club (cudgel) can leave a bump in the bullet base. Examine the bullet base to see if you're tearing divots from the bases. If you are, let the sprue harden a bit longer (read an extra page from the book of instructions) before breaking the next sprue. You could also cool your sprue plate a bit more by touching it to a cool, damp rag.

[ohland]

Examine the bullet base to see if you're tearing divots from the bases. If you are, let the sprue harden a bit longer... You could also cool your sprue plate a bit more by touching it to a cool, damp rag.

I let the puddle go from shiny to frosted and wrinkled / sucked in. Started to cast with two moulds the last time, seems promising.

[bhn22]

The sprues change colors a few times, it's kind of neat. I normally see three changes, but I've been told by others that they see up to five changes. They must have really good eyes. I have a few favorite designs that I cast for, using two identical moulds. It's been faster, and more productive than most four cavity moulds I've tried.

[ohland]

Break your sprues by hand. Breaking sprues with a club (cudgel) can leave a bump in the bullet base. Examine the bullet base to see if you're tearing divots from the bases. If you are, let the sprue harden a bit longer (read an extra page from the book of instructions) before breaking the next sprue. You could also cool your sprue plate a bit more by touching it to a cool, damp rag.

Break sprues by hand? Do tell me more.

When I ran two moulds, after I got things going: Grabbed #1, cut the sprue, dropped the boolit, poured #1, set 'er down. Grabbed #2, cut the sprue, dropped the boolit, poured #2, set 'er down. Repeat.

[DLCTEX]

I cast wearing heavy leather gloves and cut the sprues by pushing the sprue plate with my thumb. If the sprue is leaving a bump I push down on the plate as it cuts. Bullplate lube or synthetic two cycle oil on the could top and the sprueplate bottom allow me to cut the sprue early without smearing or tearing. This really helps if there is zinc in you alloy that makes sprues hard to cut.

[gwpercle]

And make sure the plate is snugged up to the mould. When I start seeing base bumps from the sprue I tighten up the screw.
Gary