Does this sound right?

[vanilla_gorilla]

I've been having problems with getting good, filled out bases with my .44-250-K mould. I get rounded bases, not muc, just slightly rounded off instead of nice and square. Grooves always turn out nice and sharp, though.

Yesterday, I jerked while pouring into the mould with my dipper, and instead of a stream into the hole, I pretty much dumped the entire contents of the dipper into and onto the mould. Oh well, looks like it went where it's supposed to. Cut the sprue and WOW! that's a perfect base. Try it again. Dump the whole dipper at once, and my bases are filling out perfectly. Nice and sharp squares. What gives?

[cabezaverde]

Interesting.....I bottom pour and have the same problem with the same mold. Is your RCBS or Lyman?

[fishhawk]

weight of the metal is sort of forceing it into the mould and filling it insted of just gravity pulling the stream in. thats what i think. steve k

[AZ-Stew]

You need to leave a puddle of alloy on top of the sprue plate. This gives the mould a pool of metal from which to draw as the boolit cools and shrinks inside the mould. If you watch, you can see a depression form in the sprue puddle above the hole in the sprue plate as the boolit cools. This is from metal being sucked down into the mould. This also helpw prevent base voids.

Regards,

Stew

[sirgknight]

I agree with Fishhawk. That little extra bit of weight on top of the sprue forces the lead for a complete fill. Everytime my base is incomplete is a direct result of not pouring enough lead into the mold and on top of the sprue plate. Just my two cents worth![smilie=1:

[docone31]

Absolutely!
As the metal cools, it shrinks.
It doesn't matter if it is silver, gold, or lead alloy. The only difference is the primary temperature.
Leaving a sprue column allows for shrinkage without pulling the casting. It will pull the sprue instead.
Many things are found by accident like you did.
Leave a sprue button on the sprue plate, I bet your mold fills out much better.

[vanilla_gorilla]

Now, even when pouring slowly, I pour up a heavy amount of allow on top. I use a Lee dipper and dip it full, then pour the entire contects into and onto the mould. I knew to do that from reading here about cooling and needing more alloy to fill out. That's what was so confusing the first several times I used the mould, because I was getting round bases, even though I piled plenty of melt on.

I'm wondering if the mould is not venting and when I pour a smooth stream, the alloy fills everywhere but the corners of the base due to air pressure.


Edit: Nevermind. Sounds like fishawk has a much better theory, once I slow down to read it.

cabezaverde, it's an RCBS mould.

[cabezaverde]

Mine too.

[grumpy one]

If you are pouring a full sprue with hot metal, and getting the lube grooves to form properly but not the base, one of the more likely explanations is lack of venting at the top of the mould. I had the problem and received this tip from Bass. He also has specific cures for it, though the one I used may not be for the faint-hearted. (I used a stone to create a tiny chamfer along the parting line right under the sprue plate. If you do this make sure it is a really tiny chamfer, or you will ruin your mould.)

[AnthonyB]

The 44-250K is my favorite 44 mould, and I agree with grumpy that this is a venting problem. My 44-250K works great with the sprue plate loose enough to open by itself when the mould is tilted 90 degrees. The size of the sprue doesn't matter to mine; I can leave just a thin film of alloy and still get perfect bases. I'd loosen the sprue plate and try again. Tony

[montana_charlie]

Yesterday, I jerked while pouring into the mould with my dipper, and instead of a stream into the hole, I pretty much dumped the entire contents of the dipper into and onto the mould. Oh well, looks like it went where it's supposed to. Cut the sprue and WOW! that's a perfect base. Try it again. Dump the whole dipper at once, and my bases are filling out perfectly. Nice and sharp squares. What gives?
My guess is this...
When you jerked, you took dipper pressure off of the sprue plate. That allowed the plate to lift...and air to vent between the plate and mould top...at the moment when the base was trying to become full.

Spring tension dropped the plate back on the mould when the air was gone and...Viola! A flat base with a square corner.

CM

[Calehedron]

I had the same issues with all my lyman moulds until i chamfered the top mating edge a bit with a stone. Now I get nice crisp bases after the sprue plate heats up to temp. Ive learned alot from these guys here in the few months Ive been a member.

[Heavy lead]

The 44-250K is my favorite 44 mould, and I agree with grumpy that this is a venting problem. My 44-250K works great with the sprue plate loose enough to open by itself when the mould is tilted 90 degrees. The size of the sprue doesn't matter to mine; I can leave just a thin film of alloy and still get perfect bases. I'd loosen the sprue plate and try again. Tony

+1 I find that if I leave my sprue plates loose enough to swing free on all three of my RCBS moulds they work perfect.

[runfiverun]

see what montana charlie said.

also with alot of these molds you are cooling the sprue plate quickly just hanging it open causing the lead there to cool quickly also.
just pouring extra on the sprue plate will help alleviate this problem.i like to pour so there is only one sprue not two.

[leftiye]

Agree on it being more pour pressure that might have caused the improvement. Also, CM (he's a good thimker) has a good take on how the jerk (of the hand, not the other one - LOL) could have caused venting to improve. Also agree that beveling the edges of the parting line mold halves on top can improve venting. Plus, the faster pour rate would have resulted in HOTTER metal being present at the end of the pour due to there being less time for it to cool. You might try pouring a bit hotter.

[montana_charlie]

Also, CM (he's a good thinker) has a good take on how the jerk (of the hand, not the other one - LOL) could have caused venting to improve.
I was just describing how vanilla_gorilla managed to do (by accident) what I always do on purpose...
CM