Troubleshooting a Mould -- RCBS 158 SWC

[Thomas Traddles]

I was casting a little this pm and running two moulds simultaneously. My RCBS 38 158 SWC was casting well for a bit, but then the aft mould cav stopped producing good bullets. By that I mean the fill out was awful. The fwd cav gave me no trouble. And this is the first time that I have experienced this difficulty with this particular mould. I had preheated the mould on a hot plate and the melt was running between 710 and 720 deg F. No matter how I fiddled with alloy temp, sprue plate tension and the like, I could not get that aft cavity to work. Can anybody here clue me in as to what I was doing wrong? Thanks.

[dh2]

heat the mold up on top of the pot

[toallmy]

Venting would be my guess .

[rintinglen]

Carefully check the vent lines for obstructions. It sounds as if lead was forced into them and is preventing the air from leaving from the corners of the cavities's edges. Given that the cavity had been working well, this seems to be the most likely cause. You may find that speeding up your casting tempo will help, but in the long haul I think heating the mold very hot and chasing out the vent lines with a bamboo skewer would be your best shot at curing the problem.

[jcren]

+1 on venting. I have had this happen if I overlube pins. Lube migrates to vent lines and burns there. May have to scrub like crazy to get it venting again.

[Thomas Traddles]

Thanks for the advice. I will give it a shot. Interestingly, I had the mould out for a casting session this a.m. and when I placed the mould against the spout and poured, I got perfect fill out. But I will clean the mold, nevertheless, and see if that rectifies the issue I stated in the original post.

[runfiverun]

for sure it's venting then.

check the sprue plate too, see if it's laying flat on the mold top.
the screw can be tightened or loosened and this changes the angle it rests over the holes.

if you don't find anything with the vent lines or the plate.
take a sharpening stone and run it down the corners of the mold block from the edge of the cavity out towards the edge of the block at a 45* angle.
just 1-2 light passes on each side, that should open up an air channel right there.