I've noticed that this fellow and I do some similar things - but he's a better writer. I checked with the moderator on CB-L and apparently it's OK to repost this file.
From: <APitfield@aol.com>
To: <CB-L@yahoogroups.com>
Subject: Re: [CB-L] Re: Wrinkled bullets
Date: Sunday, September 24, 2006 9:38 AM
As the saying goes "there is always more than one way of getting to Rome". I have been heavily involved in bullet casting for the last 5 years – read commercial
caster - and do anywhere between 250,000 and 500,000 round balls per year plus normal pistol and rifle bullets in various alloy hardnesses from 10 to 22 BHN.
Basically, it's all bottom pour casting and in order to maximize quality and productivity, I need to cast at the lowest possible temperatures. This way there are less
issues with bullets or balls sticking in the moulds and less problems of lead build up either between the mould parting faces or between mould top-face and sprue
plate.
But in order to get consistent bullets without wrinkles I need to pay particular attention to the flow of lead. By this I mean the stream of lead alloy coming out of the
orifice needs to fall perpendicularly and directly into the hole of the sprue plate. If the alloy stream runs off the sprueplate into the mould, I will surely get wrinkles in
the nose section. I don't let the lead overflow, but ensure there is a generous excess of alloy sitting on the sprue plate well.
If you flux regularly in your casting pot it is unavoidable that some of the dross will finally accumulate at the pour spout and affect the alloy flow. First signs will be the
flow rate will reduce, it might be like a continuous stream of droplets and the steel plunger will not seal properly and droplets will form between castings. Also, when
you start to cast, the alloy stream will initially show signs of "vortexing" before going back to a straight perpendicular flow.
One way to get round this is to open the pot spout to say 3-5 mm. Which simply means the "clogging" effect takes longer for it to become evident. The detrimental
flow effects are more distinctive in lean alloys as used for muzzle loading bullets and roundballs. A lot can be said at this point for having two pots, one as a pre-melt
and another for casting only. Certainly it pays to use the cleanest alloy possible. I now try to avoid any fluxing in my casting pots for these particular reasons. As a
grey skin (lead/tin oxides) appears on the surface, I will generously spoon this off into the pre-melt pot and flux there.
Similarly, opening the hole in the sprueplate to say 5-6 mm. will give more leeway for getting the alloy stream into the mould cavities without touching the sprueplate.
In my opinion the sprue hole doesn't need to be any bigger than this.
Before opening either holes on the spout of the casting pot or the sprueplate, check the spout for blockage. Best of all empty the pot and clean out with boiling
water - don't add detergents! You'll foam at the mouth in more ways than one! You'll find that plain water in the pot (1/3 to half full) and then allow to boil with pot
heating system will get out a lot of dross and other rubbish. Check that the spout and steel plunger are clean. If everything is in good working order the plunger should
give sufficient seal to stop the water running out.
If this doesn't work try the following. Empty the remaining water out of the pot. Take a plain soap bar as mentioned in the previous postings and put some slivers of
soap down near the pour spout hole. Turn on the pot and allow the steel plunger rod to sit in the well freely. As the soap sizzles and starts to melt, rotate the plunger
and move back and forth so as to mix and flux the remaining "rubbish". Then add about 1/2lb. of clean molten alloy and flush the whole lot out. If you don't have
molten alloy to hand just use some scrap bullets or whatever and let them get truly molten before flushing. Do this a couple of times and then check the sealing again
with molten lead. If the plunger rod seals well and no droplets appear then afix the plunger rod to the pot as normal. Add more molten lead and check the flow of
alloy and look for tell-tale signs of dripping.
The more modern casting pot has a facility for adjusting the flow rate of alloy. The flow rate should be decreased so that the alloy just starts to dribble and then
increased back up slightly so that a continual vertical stream is evident. If you do these adjustments with a "rich" alloy you might have to adjust again when going
back to a leaner alloy. Similarly, after several casting sessions you might notice the flow decreasing - this is normal and just indicates that dross is just starting to build
up again. Regulate the flow again. At some stage this adjustment might not be sufficient and you might think it's time to clean the pot again.
But before you do this, try another trick. Open the flow adjustment to maximum and now allow the molten alloy to flow continuously into a small Lee ingot tray or
similar. Actuate the steel plunger every second or so and you might find that this helps flush out the pour spout enough to avoid doing a complete cleaning operation.
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Originally Posted by geargnasher
