RCBS 09-115-RN Poor Mold Fillout - What's the Fix?

[Hanzy4200]

I will preface this with the fact that I own 15-20 molds and have been casting for a few years. I'm not a expert, but I'm no newbie. I picked this mold up from a member here a month ago. It was in very good condition. For the life of me I can't get the rear cavity (handle end) to fill out at the base. It will run great for 5-6 casts, then as soon as it gets moderately warm, no base. I've played with lead flow, tin content, the usual culprits. Any ideas?

[Bazoo]

Sounds like one of two things, venting problem or maybe a poor sprue puddle. I have this issue with the last hole if I let the sprue puddle run off the mould or the puddle isn't large enough. Have you tried running that hole first? Or only that hole a while to see if you can pin it down?

For venting ,Break the sharp edge of the inside of the mould blocks top with a sharpening stone. Very little or the bullets will fin.

[beagle]

That's what I'd say as well. Vent first and if that doesn't work, try filling from the other end of the mould every other cast. I have a 200 grain .35 mould that does that too me so I have to alternate ends that I start pouring from. Cantankerous rascal starts doing right then and lasts for a while. Then starts it again. I think the RCBS blocks being larger dissipate heat quicker. Mine's HP'd in the first cavity so removing the HP cavity pin slows me down a bit on casting tempo./beagle

Sounds like one of two things, venting problem or maybe a poor sprue puddle. I have this issue with the last hole if I let the sprue puddle run off the mould or the puddle isn't large enough. Have you tried running that hole first? Or only that hole a while to see if you can pin it down?

For venting ,Break the sharp edge of the inside of the mould blocks top with a sharpening stone. Very little or the bullets will fin.

[MT Gianni]

Beagle knows stuff. I would definitely try reversing fill order before I started adding venting.

[Bazoo]

Could be what you're lubing the sprue plate with is blocking the airflow too if there is no top vent. I use graphite.

[Hanzy4200]

I have tried reverse filling. I've tried even single filling only this cavity. I lube with full synthetic 2 stroke oil, but very minimally. Is it potentially due to sprue plate over tightening?

[Hanzy4200]

I have also noticed some minor finning. More pronounced if I dont make a conscious effort to keep handle pressure. Mold was sold as new, but it was clearly used at some point, though very little. I've just never had issues with any of my 5-6 RCBS molds. Always have been great molds with zero issues.

[Martin Luber]

Some moulds, like long and thin boolets, l have to pressure cast; put the mould onto the bottom pour nozzle then pour. If that plugs your nozzle, start the flow first then shove the mould onto it

[mattw]

Ok, been casting 30 years and have seen this happen. 3 things I have seen cause this listed in what I would consider most likely to least likely. 1) sprue plate to tight. It really should almost fall open and closed, if to tight it will not vent right. 2) Sprue plate is not flat, this causes venting issues. Try lapping it on a sheet of glass. 3) Bent sprue plate hinge screw, this causes the pressure on the plate to not be even and will cause venting issues.

Pressure pouring is another option, some moulds just have to have it. This can be done with a ladle or bottom pour pot. If there is to much pressure, you will get finning. The mould may have been dropped, this can cause all kinds of weird issues. I do not have this problem with any of my RCBS moulds, the biggest problem with their moulds seems to be dropping undersized. I usually end up lapping them a tiny bit.

[MT Gianni]

I had a problem with an RCBS mold that went away with ladle casting. To me it made no sense but that was 5+ years ago or so and my bottom pour has been converted to ladle for 3 years.

[Conditor22]

whenever I have moldproblems, the first thing I do is scrub the mold first with acetone or brake cleaner then dawn dish soap and hot water.

I normally use a stiff nylaon/plastic brush but on occasion have use a brass brush on a steel mold being careful around the cavities

mattw has a good point there. many people clamp the sprue plate down way too tight. I like to have at least 2 wave washers holding my sprue plate down and only snug the screw down to where the sprue plate swinge easily.

many molds that the sprue plate is sinched down to much will wear the top of the mold tight under the sprue plate screw/and/or not lube the sprue plate screw enough because they hate getting oil in the cavities. Using a needle tip dropper bottle solves this problem

sprue plate too tight or not lubed enough


I recent had the sprue plate on a 4 cavity mold buckle a little so I took the sprue plate off, set the 1/2 thick top off an old bathroom scale on my bench and set a sheet of 80 grit wet/dry sandpaper on the glass. then holding the sprue plate flat I sand until the sprue plate is flat again. Now I switch to 400 wet dry paper and smooth the bottom of the plate.

you can do this to the top of a mold also to flatten/smooth things out ( I had to do that on the mold pictured )

I preheat my molds ona hotplate to 400° (I turn the hotplate on when I turn the casting pot on.
I cast between 685 and 720° (except pure gets 750°)

IF I don;t get the desired fill and the aloy is up to temp and the mold is up to temp I will toss in .5 to 1 oz of tin/pewter.

What alloy are you using? the softer alloys require a little more temperature (Less tin & harder aloys melt at lower temperatures)

make sure you have a good flow of lead from the pot (if not the alloy may be dirty/ the room may be too cold ie fan blowing on the pot will plug up the spout. I've found that the spout on RCBS pots are thicker and hold the heat much better than the spouts on lee pots. Another reason you spout may plug is if your casting rythem is too slow) a small propane self igniting torch works great for warming the spout

another cause of incomplete fill is not clearing the spout (especially if you have a drip on cool lead hanging from it before casting each time this cool piece of lead won't melt and causes incomplete fill

when you cast, you should alternate the ends of the mold you start from. this helps keep the mold at a more even temperature.

ONLY AFTER I have tried everything else will I take a sharpening stone or fine diamond hone and lightly break the top inside edges of the mold.

Pictures would help us diagnose the problem.