sprue venting problem?

[kokomokid]

Just got a new single cav RCBS mould for my 40/65 with thick sprue plate and cant get good base fillout? Casting 40-1 and tried 720 to 810 temp. Tried WW and boiled Mould , brake cleaner etc. Sprue plate has good machine marks that I used carpenter pencil on came back and used brass brush to open up vent? Do I have a vent problem??

[HORNET]

It could very well be a venting problem. Try taking the blocks and polishing or filing a VERY SMALL bevel at the top edge of the inner face of the cavity blocks. All you need is maybe a 0.005" X 45 chamfer to allow the air/gas to get out. If you can see it, its just about enough. I use some 400 grit wet-or-dry silicon-carbide paper and drag the block about 1-1/2 inches with light/moderate force. It's easier to take more off than grow it back on......try one side then both if it still doesn't seem to be enough. Make sure the other vents are clear, I drag the point of an X-acto knife blade along them backwards to scrape out any crud...

[excess650]

Before you do something undoable, like venting the tops of the blocks, try pressure casting, and leave a good puddle on top. I prefer pressure casting with a Lyman ladle, and with the spout drilled larger for 350gr+ bullets. Mate the spout and sprue cutter with the mold turned mostly sideways, turn up as a unit, break contact long enough to allow alloy to run out, and then re-make tight contact. Do this over the pot so any alloy that runs off goes back into the pot. Its easier done than described, but will make consistent weight bullets if you can maintain technique and rythm. I cast my BPCRS bullets 25-1 and generally 720* in a similar mold. Your thermometer and mine may not be calibrated the same, so adjust accordingly.

I used pencil on tops of the block and under the sprue cutter for years. I'm inclined to think it inhibits venting by filling the lines in the tops of the blocks. I've since switched to Bull Plate and won't go back to graphite.

[462]

I have an RCBS 30-180-SP that needs to be very hot, to get base fillout. Pre-heat the mould so that it is HOT.

[MtGun44]

Make sure that the sprue plate is very free to move - this gives a bit of venting.

Too tight is not helpful.

Bill

[mooman76]

Like stated leave a good puddle on the sprue if you are ladle casting, If you are not try ladle casting and try loosening the spue plate. Make sure when you preheat the mould you are getting the sprue plate hot too.

[Hardcast416taylor]

Had a similar problem with a Saeco .45 wadcutter mould. I tried about everything with no luck till I loosened the sprue plate to almost ridiculous loosness. Took care of the base fillout problem and surprisingly didn`t cause slop lead under the plate as would normally be expected.Robert

[GabbyM]

Those big bullets like to be pressure cast in order to get good groove fill out and reduce shrinkage.

[RobS]

Make sure that the sprue plate is very free to move - this gives a bit of venting.

Too tight is not helpful.

Bill

+1 on this one. The sprue plate really only needs to be tight enough to fit flush with the top of the blocks. I adjust mine so the sprue plate opens up freely with a slight push of my finger. Many molds with poor base fill out can be fixed this way.

[bobthenailer]

try filing a slight bevel on inside of mould blocks halves , as stated previously by hornet. go slow! and try it out !
dont open up the sprue plate holes!!!!
i have about 25 + moulds from saeco, rcbs, lbt & mountian moulds . i have done this to every mould that i have , and 6 of the moulds are 8 cavity saecos .
i orgionaly got the idea from vierl smiths aka LBT book on cast bullets around 20 or so years ago.
i dont remember which book as ther are 2 updates from the orgional , and i have all 3
bob

[Le Loup Solitaire]

RCBS molds usually are not problematical although any given mold can be. The sprue plate should not be tight on the tops of the blocks. It should sit flat with no slop but should swing free on its own weight when the blocks are tilted. Air needs to be able to get out under the plate. A second consideration is the size(diameter)of the pour stream. If it is too thick and is equal to or more than the diameter of the pouring hole then it is going to trap air and effect the fillout. Another factor to keep an eye on is casting temperature....too cold = poorly filled out bullets. You also need to pour a puddle on the top of the sprue plate for as the bullet cools it shrinks and needs to be fed some melt to ensure proper fillout in the base area otherwise it can also result in voids below the base surface. A trick/gimmick used by some casters with success is to gently allow the blocks to fall a short distance onto an ingot for example while the sprue plate puddle is still liquid; the jolt jars the lead downward by inertia and is believed to improve fillout. A small percentage of tin, 1-2% does a lot to help sharp fillout. If the vent lines are clear and the blocks are in good shape then the above factors should yield good bullets. If not then check for contaminated metal...namely some zinc to start with. Even a little of that quickly ruins good bullet fillout. Keep your melt fluxed and clean and at the right temp range. With all of the above in order tou should have no problem. LLS

[HeavyMetal]

Dip the corner of the block in the melt for a slow 10 count then dip the sprue plate for a slow 10 count then cast and check the base after you cut the sprue but before you open the mold.

Base should be completely filled around the circumference of the cavity. You may have to dip the sprue plate every other cast wih a big boolit.

Try that before you mess with plate tension.

[justingrosche]

Bevel this, file that, enlarge holes. You got to be kidding. Its not the mold, its the caster. RCBS blocks are a bit hunk of iron, it takes a while to get them hot. Get it hot and it'll fill.

[cbrick]

I agree, before removing metal from the mold make sure the sprue plate isn't too tight and pour a large sprue puddle on top of the plate before you quit pouring. Might also try pouring a bit faster. Permanently altering a mold should be a very last resort especially with a quality mold such as RCBS.

Rick

[LAH]

Make sure that the sprue plate is very free to move - this gives a bit of venting.

Too tight is not helpful.

Bill

I like swinging sprue plates.