Hello

I was woundering how much weight differents can you have in a bullet before you know that their is air pockets in the bullet? I am making 158 grain bullets. Most of them weight about 154.0 to 156.0 gain. Is this to much differents or is this about right. Thank for the help

Hod :cool:

You're talking about a difference of just over 1% in your bullets. I wouldn't worry about it for 99% of your shooting. For that special hunting trip you can segregate them by weight and have a box of all the same weight. It will make very little difference, but you'll feel better about it.

Can't tell them from the outside, but there are two types of air pockets (bubbles if you like).

IF you were to section some of your light-weight bullets will find one of two types of voids. The off-center "bubble" is hard to fine as you are sectioing the bullets in only one plane....and this one is probably the most damaging to accuracy as it is both light and off-center.

Ther other type is a kind of radial cavity. A shrinkage voild usually running like a tear up the middle of the bullet...irregular in shape, usually more like a ragged lpine in the center of the bullet than anything else. Are less damaging to accuracy, but as you can't tell them from the first type unless you cut the bulletws in half, that's not information you can use.

Seem to be more common with (1) cool bullet molds (2) multi-lube-groove type bullets.

So basically, your best (most consistant) bullets are from the middle of you casting run...once you get the mold up to good casting temperature and get into your "casting goove".

Seem to be more common with (1) cool bullet molds (2) multi-lube-groove type bullets. Always thought that air bubbles were caused by the molten alloy not hitting the sprue hole directly and thus swirling into the mold cavity. Have found surface bubbles on both the sides of the bullet in the area of the grease groove and on the base of the bullets. Sometimes the bubbles are covered by a thin coating of easily identifiable bright silver alloy.

Melt and mold temps will play a roll in giving you voids. If the melt and or mold is too cold, the lead will be setting up before you finish pouring the bullet and you'll get voids from incomplete filling.

Plugged up vents will also cause voids because the air cannot get out of the mold fast enough.

Marshal, bigger bullets often pour best when you let the melt run off the sprue plate, not really swirling in but not filling the sprue hole completely while pouring. This lets the air come out the sprue hole and relies less on the vents to handle the volume of air trying to escape. Voids found on the circumfrence of the bullets usually indicates vent problems but can also be from the casting alloy dribbling into the mold and just like if you dribble water into a glass, the bubbles are pushed to the outside away from the point of pour. If you're having problems running the melt off the sprue plate chamfer into the mold, you should try some of my sprue plate treatment. Less than the volume of a "drop" of this stuff on both sides of the sprue plate will definitely impress you.

Aluminum molds cool quickly so you need to run a little higher melt temp and keep that mold cycling fast so the heat stays in it. A way to cheat if you don't pour fast with AL molds is to clean the outside with scotch pad and give it three to five coats of a quality high temp engine paint. This acts like an insulation blanket to help keep the heat in.

Some mold alloys expand more than others too which can also lead to weight variations, this can be verified by comparing the bullet OD in relation to the weight.

I have two identical Lee molds purchased about 5 years apart. Bullets cast in one were running .0015" bigger than bullets from the other using the same alloy from the same pot of melt. I wax pressed the molds and found the cavities to be well within tolerance, one being only .0002" bigger than the other. The difference was in the alloy Lee happened to get from their supplier, it expanded a little more and thus dropped a little bit bigger bullet. It worked out great for me because I only had to lap the one mold .0005" to give me the .002" larger size casting I was going after anyway. Point is, no matter how well the manufacturing process is controlled, the variations in the raw materials coming in can make a big difference in the final result. Every mold, like every gun is going to be specific unto itself through no fault of the manufacturer.

Another thing is your casting alloy. The amount of Sn, As, Sb & Cu contained in the alloy your using can make a big difference on the creation of voids through air bubble inclusions and this has to do more with the casting temp of the melt than anything else. If you're getting a lot of weight variations but next to no size variations, raise your melt temp in 10°F incriments until you bring your as-cast consistency into tolerance. If you get to the point where you start to "frost" the bullets but still have variations, slow down your casting rhythem and give the mold a longer cooling cycle with no bullets in it and open cavities.

BTW, the harder the alloy, generally the lower the melt temp should be. Pure Pb or very low alloy Pb will like higher temps in the 850-880°F range. Alloys with higher tin contents will generally run better closer to 800°F. Cu & Sb free alloys will often drop cleanly in the low 700° range while alloys with a high Sb or Cu content sometimes won't start casting good till you get into or above the 900°F range (this is where you run into exposing yourself to inhalation hazards too, don't get over 900° w/o the proper equipment!)

Always thought that air bubbles were caused by the molten alloy not hitting the sprue hole directly and thus swirling into the mold cavity. Have found surface bubbles on both the sides of the bullet in the area of the grease groove and on the base of the bullets. Sometimes the bubbles are covered by a thin coating of easily identifiable bright silver alloy.

Given that swirling off center pour and a cooler mold, that would promote bubbles....mold hotter, so that the lead solidifies slower, should stop that. Have had molds that just refused to cast unless the pour was on center...some that refused to cast unless it was off center. IS no one standard way to cast, each mold has preferences to temperature and pour style.

Easy to find the voids that are near the surface...but rest assured, the lights ones (1) have a void soimewhere in them or (2) are not well filled out and the loss of weight is from the missing "edges".

Markkw and Ribbonstone,
Thanks for the great info! Seldom get surface bubbles but will get maybe two or three during a casting session. When I can see any bright silver spots on the bullet, I poke at it to see if it's a bubble. Sometimes I miss the ones in the grease groove but these usually show up when I lube/size as the lube collapses the bubble and I can feel it through the tool handle. No way to spot the internal bubbles except to weigh each bullet and have no need to do so anymore with plinker bullets.

My biggest problem when casting is slag removal from the alloy. Seems I stir and flux quite often yet the alloy keeps giving up slag. Production of good bullets would increase if I could control this aspect of casting better. Any tips here?

My approach on the constant oxidation and slag rebuilding is to flux the mix well, then leave the dross on top of the melt until the pot is nearly empty. It forms a surface barrier to oxygen and slows the formation of dross. Of course this only works with a bottom draw pot, if you use a dipper, you just have to constantly flux and clean off the surface, or place cat litter on the surface to minimize the exposure to oxygen.

Marshal,

Not sure what you mean by "slag". Are you getting thick dirty crud or just the thin skim film of brownish gray dross? If you're getting more than a skim coat, you're flux is not working properly or you have some kind of contamination. I ran into a few odd things, got some orange colored stuff that looked like fluffy ash one time, another I got a black almost oil soot type crud. Never did figure out what either was but with a good fluxing and some cook time, it cleared out.

If your melt is running too hot, you're oxidizing the Sn and possibly cooking out some of the Sb if it's in your alloy. Normally, these are what gives you the light tan colored skim film, other small amounts of impurities will cook out and turn that skim layer darker more like a brown but it should not be thick and dry looking. If you're only getting the skim coat, don't worry about constantly taking it off. Just push it off to the side with the dipper and get your lead, even if you get some in the dipper, it will stay on top and out of the mold anyway so it's not a big deal. I use a Lee, think it a Lee anyway, dipper that has the little spout on it. I added about 6" to the shaft so it's got a long handle. I leave it right in the pot so it stays the same temp as the melt. I push it down to fill it and when it comes out, it pushed the skim layer away and none gets in the dipper as the excess flows over the side and the skim film goes with it.

I've got flux agent that really works great and does not produce any smoke and does not contain any alox which is a contaminent to Pb alloys. I'll send you a PM. ... well, I can't PM you so drop me an email markkw@earthlink.net

NOt much to add to that last...pretty well sums it up.

Do know that clean metal into the pot certainly does make a casting session more enjoyable, so I do most of the "hard" work on the front end when melting scrap for igots. Would rather get most of the nasty work out of the way BEFORE I sit down to make bullets.
(Yes..some folks do cast standing up...but I'm not one of them).

454Pb, I use a Lyman Mag20 bottom pour set between 750-800F, wheelweights with a little added tin (3%), and Magma Engr Flux. Will try leaving the dross on top to see if it helps. Thanks!
Markkw, the "slag" that I get is a powdery dark grayish contaminent that shows up on the surface of the bullets. The bullets get little pockets that are filled with this stuff. Not all bullets come out this way, some look fine so I believe this stuff is mixed with the alloy and gets poured into the mould. It is soft enough to be scraped out with a dental pick. Found that frequent stirring and fluxing will bring much of this to the surface. The flux turns it into a dark gray to black "ash" like consistency which I skim off. Seems to help clean up the alloy if I flux often. Would really like to avoid having to do this. Could this be paint from some of the painted wheelweights that I made ingots from?
Ribbonstone, agree that casting with clean alloy makes that job a lot more pleasant and get better results!

The gray powder is oxide and should not be getting included into your castings. You're flux is not working to get the oxides out and keep them from being included in the pour.

You should remove the dross from the pot and use an inhibitor.

More fluxing, deeper fluxing, and scrape the sides of that pot. A garage sale or fea market sould come up with a long bladed bread knife, which once bent, makea a pretty good side-scraper. A cheap table spoon with lots of holes drilled in the bottom has been the best scum-collector for me. Write a mental note to empty the pot and clean the crud off the sides.

Thanks for the great advice guys, think I will start off by draining the pot and giving it a good cleaning. Really annoying to do the casting work and ending up with a high percentage of rejects. Appreciate all your help.