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Terry Davis 10639
04-23-2008, 09:39 PM
I recently cast up a bunch of Lyman 315 grn .575 semi wadcutters.

I was inspecting them and noticed many had an air pocket inside the tip of the hollow base.

If you look inside the open end of the bullet, it is in the tip of the open end, right where the tip of the core that forms the hollow base is located.

I am casting at 750 F +... sometimes up to 900 when I don't pay attention to the thermometer as the lead level drops, so it is not cold. I am using a lee 20 lb bottom pour furnace.

I am thinking I am opening the valve too fast and not letting the air vent, but I am wonder what others might think. Some come out with no air pocket, but most have some amount of void, some much larger than others.

Any suggestions?

Jim Brady Knap's Battery
04-23-2008, 10:45 PM
You may get arguments on this but a very long time ago I tried casting minnies with a bottom pour and gave up due to the same problems you describe. Went to the ladle and never looked back. I even tried the bottom pour for my 69 round balls and found that even though they look great from the bottom pour the weights run to a closer tolerance by using the ladle.
I'm sure other's will say they have no trouble with the bottom pour but try the ladle method and judge for yourself.

Jim Brady
2249V
Knap's Battery

Norm Gibson, 4901V
04-23-2008, 10:51 PM
I did the same as Jim.

matt
04-24-2008, 06:51 AM
i have used both methods while i like dipping for minnies it has to do more with the pot leaking. try holding the mould off center of the sprue hole letting the lead flow into the mould that should push the air out and limit the voids. i still get them no matter what i use and have found that if im not careful on my technique thats when they show up in great numbers.
hope this helps.
matt
winslows battery 9975

Terry Davis 10639
04-24-2008, 08:59 AM
Thanks. This all follows what I suspected, but sometimes some has a magic bullet answer.

Jim Strang
04-24-2008, 09:27 AM
Well guys, here's another variable -- the furnace itself.

For years I limped along with the leaky, recalcitrant Lee El Cheapo bottom-pour pots, and was plagued by these voids. Pour fast, pour slow, tilt the mould, hold it level -- no matter the variation I tried, I got bubbles.

Then, last year I had enough with the Lee furnace, and plunged for an RCBS bottom-pour furnace. Voila! No more pockets!

Why? Got me. I can't think of a good reason, other than the facts that the RCBS spout doesn't get leaded up like the Lee does, or the heat seems more consistent. All I can go by is the result, and the result is no more holes.

macvcallsign
04-24-2008, 09:43 AM
Have been using bottom pour pots for 30+ yrs and do get air pockets but have lessened them to a minimum. First someone told me yrs ago to cut back the point of the base plug to a flat, about a 64th to max of 32nd of an inch on a mold that was giving me this problem. This helped a lot. If the base plug point is already shallow keep the cut to a minimum. Also I found that by holding the mold half an inch or so below the pour spout and open the spout slowly so you don't get the full force of the lead flow will allow the air to escape better. Makes for a more consistent bullet weight also. Sometimes I tilt the mold slightly so the lead flow does not hit the tip of the base plug directly.

These things seem to work for me. Sure, I still get a pin hole now and than. I just dump them back in the pot and keep going. I tried casting with a ladle when I first started skirmishing and found it simply too slow.

Well, that's my 2 cents of advise! :lol: Might work for you. Have fun and don't get frustrated. It's all fun in the end! :)

Chao,

Dennis, 4th Ky Cav.

Phil Spaugy, 3475V
04-24-2008, 10:00 AM
If thou wants their balls to score,

Ye must ladle pour !!!

Philo

Jim Brady Knap's Battery
04-24-2008, 10:44 AM
When loading for smoothbore





take this advice






The dipping in lube






must be done thrice!





Burma Shave






Jim Brady
2249V
Knap's Battery

RaiderANV
04-24-2008, 11:17 AM
This question comes up like every couple months. I tried all the answers and none really worked. The cut the tip of the base plug and holding the mold on the slight angle so the lead hits the sprue hole at an angle and the lead swirls in and the rest.

My air pockets stop 99.9% of the time when I started pouring the bullets AND leaving a big pile of lead in top of the mold while pouring. I can only guess it's that lil extra weight that rids the air pocket.

But then again I've cut bullets from different folks in half that looked just fine and found air pockets inside their rounds

I wieghed the rounds with air pockets and they ranged 15 grians either direction. I then shot them all and the impact didn't change a bit so go figure.

NJArtillery
04-24-2008, 12:53 PM
I wonder if this problem is really an air pocket problem or if it's a lead shrinkage void. When we cast cannon shells in lead we always deal with lead shrinkage as the lead cools, and this causes voids similar to what you describe.

I think it was Thomas Edison that theorized that it was impossible to cast a 1 foot cube of solid lead in a single casting. When an attempt was made to prove him wrong, Edison simply came out with a trusty scale and weighed the cube, and proved it was too light to be fully solid due to shrinkage voids...

I tried to find some reference to this on the internet but came up short. I'm pretty sure that's what I learned when I visited the Edison Museum in West Orange, NJ.

Jim Brady Knap's Battery
04-24-2008, 05:34 PM
I have noticed that when the mold is up to temp if you cut the sprue as soon as the puddle seems to harden you will get a pocket. If you give it another few seconds to really set up it will stop.

Jim Brady
2249V
Knaps Battery

Gordon Bailey
04-24-2008, 11:47 PM
My belief is that this is a shrinkage void. The spew freezes off before the rest of the ball solidifies and it forms a shrinkage pocket in the remaining molten metal. The tip of the pocket is a prime cantidate as it is next to the thickest pst of the ball, and can transfer heat only out the bottom.To fix it you have to keep the spew hotter longer than the tip of the cavity. With bottom pour it is hard to control. The RCBS bottom pour works better for the same reason the spout does't freeze off as offen, better design.
I ladle pour and keep the spew hot by letting the lead from the ladle continue flowing over the top plate (Spew)back into the pot. For Minie' balls I use the full ladle in keeping the plate hot. Its slower but once the mold is hot I have near 100 % void free and 97% within a 3 grain spready. I suspect the remaining variation is associated with lead additions, fluxing etc. that breaks the rythum.

Terry Davis 10639
05-07-2008, 11:17 AM
just to follow up, I tried letting the lead hit the sprue cutter and flow into the mold more slowly.
I experimented a bit and was able to turn out consistant bullets without air pockets. I had to throw the occasional odd bullet back into the pot, but overall it went well. It just means I need to slow down a bit and let the air escape.

I weighed them and they were pretty much within 1 grain. Most were within a couple of tenths.

Thanks for the advice.
Terry

Gordon Bailey
05-07-2008, 12:08 PM
Terry

Glad you got it working.