Home Forums Reloading Bullet Casting Spru Time

After your mould and alloy temp and mix is good to go and you begin to pour in earnest, how many seconds do you wait for the spru to harden? Assume a 2 cavity iron mould. Is there a different amount of time for a brass mould?

It's kind of subjective. I generally wait and watch the sprue for it to thoroughly "ice over", and then some, before knocking it open, especially if running an antimony alloy - I hate getting antimony induced smears on the blocks and sprue plates. Amount of time varies by sprue size, temperature, and mold construction - you have to experiment a bit to satisfy your own circumstances.

With simple binary alloys (ie: tin/lead) without antimony in them I don't wait as long. As soon as it solidifies it gets popped off.

I generally like to cut immediately after it goes from a wet to cured appearance, since I generally heat treat everything.

I don't recall if it was Seyfried, Venturino or Veral, but they described it as half cut, half tear. This leaves a flat base.

All tear and you have a crater in the butt, cured too long and you have a raised sprue.

Smears can be cured and prevented with some carpenters pencils.

A thin scribble atop the blocks and underside of the plate (don't forget to blow off the crumbs and keep them out of the cavity) keeps smears from appearing and can also keep steel and iron rust free.

But yes, it's definitely subjective and depends on some vudoo.

Easier to get a tear/crater with high antimony alloys, methinks, due to strict inattention toward applying the voodoo of casting cadence.

I've used the lead pencil trick and it works. Also a good way to lube the rubbing surfaces of powder measures.

Another protocol overlooked by many is tightness/looseness of the sprue plate. I like a sprue plate to swing closed of its own weight, or at least nearly so. By pressing the nozzle of the furnace or dipper firmly against it before starting the pour ensures uniform flatness plus allowing for a teensy bit of air venting. Over tightening can induce a bit of cockeyed-ness to the bullet base, exacerbated by any buildup of smear also. All of the grizzled old bullet casters I've known followed that protocol.

I don't much like beating on my molds with anything and thus don't knock my sprue plate open, I swing it open with my ladle hand, palming the mold and pushing the plate with my thumb. You get a feel for when the time is right. Too soon and it opens too easy and usually leaves a smear. Too long and it's pretty difficult to cut the sprue with any kind of alloy. Just right and you feel a little snap when it cuts, and it cuts clean. As I'm pulling the plate open I'm catching the sprue with the palm of the same hand and I drop it right back into the pot.

Thick welding gloves required......

A good protocol, but one I never took a shine to (especially with gang molds). I confess to being a sprue plate knocker, and still use the hefty little piece of rock hard curly maple shop scrap my Gramps gave me 50 years ago. It's mightily chewed up and mis-shapen after knocking untold tens of thousands of sprues but I would cry if I had to replace it!

Old habits die hard.....

With multi-cavity molds I pour a continuous sprue, kind of like soldering them together one to the next after the cavity is filled, so everything is connected and I have one piece to deal with instead of multiple little sprue gobs. The only true gang mold I have is a six cavity 480 roundball mold and the same pour technique works fine with it. Everything else I have is single or double. I pour one sprue with the doubles. Just makes life easier.

I’ve always cut the sprue just as fast as I could because I wanted to cast as many bullets as fast as possible. (Yes, I’ve opened the sprue with a gloved hand. ) And I also didn’t like to beat on my molds. I’ve recently slowed down, at least with rifle bullets. Letting the lead harden completely makes more accurate bullets and I can prove that with my rifles, I can’t prove it with pistols, lol…. I’ve also found the bullets drop out easier after they’ve cooled a little more, I think they “shrink” away from the mold and release themselves.

I get the best of quantity and quality (of slower casting) by casting with 2 or 3 molds at a time. With this method they are always cool enough they have to be beat on a little but I’m not as concerned with beating on rifle molds because I don’t need as many bullets and i doubt I’ll ever beat them enough to wear them out.

I also pour a continuous sprue like Feral_American does for the same reason.

The last time I cast with my Lee 6 cavity mold I was putting a small c-clamp on the far end because I was having a hard time installing gas checks on some of the bullets. Thought maybe the mold wasn’t being held tight enough to make 6 consistent bullets. I haven’t proven this out yet, but I will one of these days.