Casting Minnie' Bullets, kink in my casting technique !

[heelerau]

Gents could not quite seem to find the right spot for this query. I have been casting minnie bullets since about 1973 and over the years have got pretty good at it. After eyeballing for faults I get a about a 4 grain variation and these bullets are about 600 grain with a reasonably deep hollow and a fairly thick skirt.
I seem to of late got a kink in my casting technique and keep getting shrinkage coming up from the top of the base plug, normally you will get shrinkage with really hot lead down from the sprue plate, particularly if you don't leave enough of a puddle there.
I did clean the pot and put a new charge of 99.98% pure bar lead in , just in case some lino type may have got mixed into the works. Bullets form nicely in the mould, and I am finding the same with my Prichett bullets as well. Has anyone else had this happen and worked out what was going on

cheers

Heelerau

[runfiverun]

you might have got some lead with some calcium in/on it too.
it could have been as simple as they got wet with hard water and it picked it up from that.

[quail4jake]

Well, you've stuck upon one of my great struggles in life. I may even write book about this I'm thinking about a title like "Mein Kampf" or something....

Right! Well we really need a solution to this because I've seen this phenomena all my life! That's because my life, as I see it, started in 1971 at 10 years old when I first melted dug up boolits in a soup can on the gas stove and cast them in a suppository mold from Dad's pharmacy and fired them out of a DGW percussion 28 ga smoothbore. It went on from there directly to a lee "minie" ball mold firing a NA '63 Springfield repro. and so on. Now looking back at those last 46 years I have had trouble with the infamous "minie ball bubble" intermittently and here's what I've learned. BTW I killed a deer with one of those suppositories!

I've talked to NSSAers who cast and fire expanding balls (the US ordinance dep't term for "minie type balls) successfully and was told that the bubble doesn't significantly effect performance and either don't worry about it or weigh and discard beyond a certain tolerance. The truth is that when I use the right lube, standard 60 grain charge of FFFg and size the boolits to bore dia. minus .001" even my badly corroded NA Springfield groups 6" at 100 yds, so I can't argue.

Even boolits that don't appear to have the bubble will often have some void inside if you cut them in half!

Core pin shape doesn't seem to alter this except in the case of the Lyman Parker Hale style which has a large broad flat top pin, I have cast boolits with that and can't find any void but they weigh over 570 gr and don't group well.

So how did Union arsenals overcome this 150 years ago? They didn't, the expanding balls made by Frankfort, Washington Naval Lab etc were swaged. If you ever get to see one that's not deformed or corroded they are a masterpiece!

More NSSAer advice: try adding Sn to the pure lead we usually use. I am currently working on an alloy study which includes 40:1 (2.5% Sn), 60:1 (1.7% Sn) and 1:100 (1% Sn) and I will try casting with the Lyman 575213OS and see what happens. 40:1 lands at BHN 7 which the NSSAers who I've talks to is still soft enough to expand reliably. That OS mold is especially difficult to fill out with Pb so I'm hoping the Sn will add castability and make nicely defined grooves.

"Cast real hot, that'll make it all work!". Not for me. Temperatures over 750 bring dross, rapid oxidation and no improvement, 680 - 700 seems to work best but remember the high surface tension of Pb makes casting difficult in general. The infamous core bubble appeared at all temperatures.

I've cast all of my expanding balls in linotype and had no core bubble and had perfect definition of detail at very low temperature. Linotype (BHN 22) is, of course, way too hard for expanding balls but this shows that the bubble can go away.

For me pouring technique had no bearing on this. I tried everything from spoon dipping to rapid pressure fill from the bottom pour pot, I even tried holding a torch flame over the sprue plate and pouring through it. No change at all.

OK, thanks for tolerating my little diatribe. Now I want to hear from anyone who has any experience with this, I could be completely wrong about all of this so please just take the anectdotal experience at face value. Someone save me from this abyss of imperfect boolits and bring light to the rest of my wretched life! (a cry for help)....and thanks!

[heelerau]

Gents, thanks for the interest. To define this a little better, I am talking a shrinkage hole that you can see running up from the base plug. And yes I guess you always get some sort of a void when casting, I to have split bullets and seen this, hence me weighing my bullets. Yesterday I had another go and poured much more quickly from the ladle, that seemed to improve matters, although still a slight imperfection at the nose of the plug. I did not consider calcium from hard water, some of this lead has been out in the weather though. I still suspect some contamination from linotype. I will be getting another ingot of lead as I have finally used up the last of my current one. . I seem to need to run the lead at a lower temp to cast. I am using a lee bottom feed pot and notice a setting of 5 seems best, 7 is too hot. My parker hale minnie mould has a flat topped plug and that seems to be a bit better than the Bugg with a rounded top on the base plug. That mould is brass, plug steel, the PH mould is cast iron.

Cheers

Heelerau

[quail4jake]

This isn't Ca contamination. It happens with pristine pure Pb and I think it may be due to shrink as the Pb cools and sucks up from the base instead of the sprue. I will send pics when I do the comparison of alloys with the 575213OS mold. Any thoughts?

[RED333]

I have tried slow pour with some and it helps a bit, still have to look close to see the good ones. Funny thing never had it happen on a Lyman 525 pellet yet, go figure.

[jdfoxinc]

I let my lead hit the edge of the spruce hole caiusing it to swirl itothe mold. Ialso cast these at 825 f.

[heelerau]

Gents seem to have got rid of the kink in my casting swing. I needed to hold the ladle about 3 inches above the sprue plate and keep pouring till the ladle is empty, I think I may have been trying to be to neat and not have to much spillage from off the sprue. My lead pot is wide enough to catch all the runoff without any going where is should not. I make sure it is a good stong stream of lead going in. I also put a tiny piece of 50/50 bar solder in. I have never added tin before, will be using these bullets on Sunday, hopefully they will be fine.

Cheers

Heelerau

[Hogtamer]

A little tin, fast pour from the ladle, big sprue, you got it!

[heelerau]

Gents a quick revisit, I am now sure that there has been a small amount of contamination from some of the roofing lead, suspect copper because still since the above even though the adjustments to my casting technique had reduced the issue of the rivel running up from the base plug, I would still get the odd one, also I have found over these last months that the freshly cast minnies have stayed suspiciously shiny instead of going dull quickly. Today I really did a good clean out of my pot, not a skerrick of any bullet melt left in it. Melted some known to be pure lead, got casting in my old manner and after the first bullet, no more rivels running up from the base plug. So I must once again go back to the BHP ingot lead which is stamped 99.8%. Just an update.

cheers
Heelerau