I have an LBT casting pot, and up till yesterday, only cast bullets out of a 309-160R Lee mould.

Having received a new RCBS 35 caliber mould for 200 gr. rifle bullets, I found that even with the pot maxed out on temp, and pouring as fast as the pot would go left me with "cold" bullets. It looked to me that not only was the pot not pouring fast enough, but the sprue was tiny for such a big bullet.

Just wondering if you fella's have any experience with this, and or recommendations?

Mass produced molds have a one-size-fits-all sprue hole. If they made the sprue hole big enough to flow well with wheelweight, then it would be extremely difficult to cut with linotype, and would also leave a bumpy sprue cut. So they use a small sprue hole and as a result you have to struggle to get good fill with wheelweight. At least, that's my humble take on the matter.

Pretty much the same story with bottom pour pots.

Recommendations? For wheelweight, I definitely prefer a ladle with a large (0.159") orifice. However, it doesn't do any good to have a big pourstream if the sprue hole is small. Drilling out the sprue hole is not straightforward because the hole has too be countersunk to a knife edge, otherwise the sprue will resist letting go of the plate. Countersinking can be difficult -- it requires a certain type of countersink cutter, the cutter is prone to chatter, and the high force required to make the cut usually results in some deformation of the metal around the hole, so that the bottom of the plate has to be resurfaced when you are done.

Most folks either 1) compensate by casting very hot or 2) compensate by using a richer alloy.

I'm not familiar with your furnace, which is apparently a bottom-pour pot? Does it have an adjustable flow rate? If so, have you adjusted the rate higher? (I know you said, "as fast as the pot would go", but I had to ask!)

My RCBS furnace works perfectly, no matter what the bullet size happens to be.

Why is the sprue "tiny"??? That should be under your control, unless you're holding the spout in contact with the sprue plate. I allow the alloy a free drop of a half-inch or thereabouts before it hits the top of the mould, and I let the sprue spread all over the top of the plate so that there's plenty of alloy to "feed" the bullet as it cools in the cavity.

With over seventy moulds on hand, I've never had to alter the hole in a sprue plate. I do own a couple of moulds that came to me in used form, and which have had the hole enlarged. Doesn't seem to make much difference.

You're on the right track in running the furnace as hot as it will go....any idea just how hot that really is? My RCBS, set at its maximum 850 degrees on the knob, actually is giving 870 by thermometer. I run this pot at MAXIMUM temp all the time, with wheelweights (and other alloys, too, for that matter). My results are great.

BTW, if the mould seems too cold, don't be afraid to stick its bottom right in the melted alloy for 20 seconds or so. Keep it there until the metal doen't stick to it any more. I do it all the time with my moulds, including a bunch of RCBS jobs, with no difficulty or damage at all.

Let us know how you make out, please?

I have a cheap, single burner hot-plate that I use for boiling water to clean oily molds. It's also handy to heat cast iron molds before casting. I set the hot-plate at it's lowest setting and put the mold on the burner. When the melt is ready to go, so is the mold. These little hot-plates are cheap to buy and handy for a lot of things around the casting bench.

Thanks! I actually should have clarified that the sprue hole was tiny, not the sprue! LOL.

I run the LBT pot at 850- 900 per the dial. I should take the temperature of the melt, but this setting has worked with other moulds. This is why I am puzzled.

I have countersunk the Lee sprue plates before with success. Being an aircraft sheetmetal mechanic in the past, I know about countersink angles, chatter, etc.

After finishing up the other night, I drained the pot, and intend to make sure I don't have a blockage preventing flow. I may get a chance to address this tomorrow, and I will advise from there!

quote:

Originally posted by Bren Mk1:
With over seventy moulds on hand, I've never had to alter the hole in a sprue plate. I do own a couple of moulds that came to me in used form, and which have had the hole enlarged. Doesn't seem to make much difference.

No, it won't matter at 850°. Nor does it do any good to enlarge the sprue hole if the pour stream remains small, as it is on most bottom pour pots. But try ladling wheelweight at 625° - 650°, as I do, and it's another story. Cooler is faster -- no waiting for the sprue to solidify, no wasted motion using a damp rag to cool the sprue, no smearing as the sprue is cut. In the second it takes to set the ladle down, the sprue has hardened and is ready to cut.

It sounds like your problem may be that you aren't getting the mold hot enough. If a mold is cold, it doesn't matter how fast or slow you fill it, you won't get a good fill. I'll rest a mold on the edge of the furnace while it gets up to temp, and then dip the corner of the mold in the melt for a few minutes.

As far as sprue hole sizes, I've found 0.160" dia to be about right, and sometimes open up smaller holes. I haven't had any problems with RCBS molds, and consider them about the best of the production molds out there.

On my ladles, I drill out the hole with a 1/8" drill bit. Seems to work just fine.

I'm just wondering though if giving that mold a really thorough cleaning might not make a difference? I've run into the same problem with RCBS molds and sometimes have had to clean them several times before I could get a good cast. Use either denatured alcohol of TCE, but use the latter outside. One, the fumes are toxic and two it is extremely flamable.
Also, after cleaning, I prefer to smoke the cavities with one of those disposable lighters.
Paul B.