How to determine a roundball moulds casting weight?

[RICKLANDES]

I am new to the world of casting and have a couple of questions. I looked thru some of the FAQ's and the like and could not find my answers so here goes...

I have a Lyman RB mould for .530 dia. 230 grain balls. I purchased lead from Rotometals (a #55 pig at 99.9%). I have yet to get a ball at 230 grains, and the Lymans site tells me the variance for a mould is +/- 5% or 241.5 to 218.5 which seems quite a range.

I have cast about 800 RB's and weighed 30 from each batch, taken the heaviest weight dropped and grain and selected only those heavier for my target work. The rest go back to the Lyman Pro-Mag.

I check lead temp with thermometer and pour at 650F to 700F. Mould is kept pristinely clean and spur cutter snug. I double flux before pour and after about 15-20 minutes of a run.

Question (I am sure some have thought finally!) How do I determine what weight ball this mould will throw? (I am thinking a good consistent average when all is as should be.)

I tried weighing each ball (just about as cast) for a short 70 ball run and about half were 222.5 to 223.0 the rest were mostly below, 2 were above.

I am after balls with no more than .5 grain variance for target work.

Any help will be appreciated!

[The Double D]

I don't know if this might help....
http://www.beartoothbullets.com/rescources/calculators/php/roundball.htm

[mooman76]

There are allot of variables in the weight of bullets or in your case roundballs. How hot the melt is and the temp of the mould. How consistant your alloy is. You may be using pure lead or what you think is pure but lead even so called pure will have small amounts of impurities and other metals. The way you cast also goes into play. having .5 consistancy is less than one quarter of 1 percent. The only real way is to weigh each bullet and the more you cast the better and more consistant you will get. I would think that weight difference especially with RBs will make little difference. it doesn't take much lead to measure .5 gr. I'd up the grain difference to like 1 gr and at that it is still half of a percent. What you do is up to you though. One thing I forgot to mention is you sometimes get a tiny bit of air in the mould when pouring which will throw your ball weight off and if you are ladle casting pour a good puddle of lead on top of the sprue plate to aid in the shrinkage for more consistant cast.

[rob45]

I have a Lyman RB mould for .530 dia. 230 grain balls. I purchased lead from Rotometals (a #55 pig at 99.9%). I have yet to get a ball at 230 grains, and the Lymans site tells me the variance for a mould is +/- 5% or 241.5 to 218.5 which seems quite a range.
Rotometals is a reputable supplier, so I would not question the lead itself. This assumes you have been using only that lead in your pot to avoid cross-contamination from other lead sources.
When Lyman speaks of their variances, they need to cover their backside in two ways:
1. Mold dimensions- The actual machined dimensions can vary from one mold to another. Any machining process has to allow for tolerances.
2. Lyman has no idea what your casting methods entail. They do not know if you cast hot, which lead source you use, etc.

I have cast about 800 RB's and weighed 30 from each batch,...
How many balls in each "batch"? As stated by mooman76, the most reliable method is to weigh every ball if you're attempting to maintain the precision you infer.

I check lead temp with thermometer and pour at 650F to 700F. Mould is kept pristinely clean and spur cutter snug. I double flux before pour and after about 15-20 minutes of a run.
You're attempting to keep everything consistent, which is good. Most crucial of all is your casting pace, or rhythm. You're using the thermometer to maintain consistent pour temperature, but a consistent pace is what maintains your mold temperature. Developing a consistent pace only comes with practice, but it sounds like you're doing well. Unfortunately, the fluxing breaks the routine and allows change in the mold temp.
You did not state whether you are bottom-pouring or ladle casting.
If you are using a bottom-pour pot, the process is easier due to reducing the need to flux.
If you are using a ladle, your goal should be to keep the ladle hot and in contact with molten lead as much as possible; remember, once the lead is away from the pot it starts to cool, and your goal is to have each pour the same temp when it hits the mold. Keep the ladle in the pot while stopping to flux. Keep the mold closed and on the pot while fluxing if you can.

How do I determine what weight ball this mould will throw?
To determine the weight a mold will consistently drop requires consistent alloy and a standardized, routine casting method.

I tried weighing each ball (just about as cast) for a short 70 ball run and about half were 222.5 to 223.0 the rest were mostly below, 2 were above.
.5 grain is very good. While striving for perfection is never a bad thing, as mooman76 mentioned, holding it that close may not even make a difference. For your application, you most likely have other variables that will have a greater impact than the minor weight variances. Patches, lube, powder, atmospheric conditions, the gun, the shooter. All have enough inconsistencies to have a larger effect than minor weight variances in the projectiles.


I am after balls with no more than .5 grain variance for target work.
Take your tight-tolerance projectiles (222.5-223.0) and work up your most accurate load. Once that is established, use that same load and throw some of the others into the mix to determine if it makes a difference.
Personally, I prefer to use as large a weight tolerance window as what the load will accurately allow. Doing so allows easier/quicker inspection and less rejects while culling.

BTW, welcome to Cast Boolits![smilie=s:

[Lotec]

D3 X .5236 X 2873.5 = weight This is for pure lead. ( D3 = D X D X D )

[CB Hunter]

RICKLANDES,

There is obviously some variation in your casting method. Just like other alloys and bullet types the metal and mould temperature must be kept within a narrow range to produce bullets of consistent weight. You also don't say, from what I saw, what diameter the mould is actually throwing. It is rare to have any round ball mould throw bullets of precisely the nominal diameter. I suspect yours are actually .528-.529. Lotec's formula puts you ball size at .528+ (.528 = 221.468 gr.).

Referring to above, I have two RB moulds of nominal .530 and .535 from a reputable maker. Both moulds throw a ball of .535!

First be sure your metal is up to temperature. If you are using a Lee pot get a better one or use a plumbers pot on the stove. Lee pots won't get hot enough to cast pure lead. Raise the temperature to about 725. Don't keep any ball that shows any signs of wrinkling, the metal and mould were not hot enough. Pure lead round balls should be the most consistent for weight of any cast bullet there is.

Don't let the post count throw you. I may have just joined the forum but have been casting for just over 50 years.

[HORNET]

RICKLANDES, Welcome to the joy(or something) of casting. I'll disagree about the Lee pots not getting hot enough, both of mine will go somewhere over 900 if given a chance. The temperature controls and method on the Lee pots would be appreciated by Rube Goldberg and vary a lot. I will agree that you need to run your melt hotter. Pure lead responds best at high temperatures and appreciates it if you can keep a small amount of flow going over the sprue hole while it cools so that the cavity has a pool of hot melted material to draw from as the casting sets and shrinks. Some on here run at temperatures of 850 or more for straight lead.

[Maven]

Rickelandes, What Hornet wrote is right on the money. It is also very easy to modifiy the bimetallic thermostat that Lee pots use. You essentially bend the lower (?) leaf down a tiny bit to increase the temperature. I think there's a sticky about how to do it in our archives. Trust me, it IS an easy and effective fix.

[RICKLANDES]

My casting efforts last eve were very successful. I poured at 700 degrees F (per a Lyman termometer...I can check againt our pyrometer some time) from a Lyman ProMag-20 furnace with a bottom pour and made sure to allow the lead flow to continue about ½ a ball volume after the cavity was filled, rather than just to fill the cavity to the top leave an overfill and stop. I also paused about 5 seconds for cooling prior to cutting the sprue. I believe the extra lead flow allowed the ball’s lower area to set and the additional flow assured that there would be no shrinkage. Balls were casting within plus or minus 3/10 of a grain. Weights were 224.3 to 224.7. Volume wise it should be a max wt of .53 X .53 X .53 X1503 = 223.7 grains for a perfect sphere with pure lead.



I also mic’ed a group of the cast balls to check them for concentricity. They appear to be within .001 or less as best I can tell turning them slowly around in my fingers while in the mic jaws. The size was .230 to .229...just a .001 variation which may be my inability to turn the RB in a centered manner more than an out of round mold.



I am quite happy with the consistency I am seeing here. I am under the belief that I may have weighed the first cast balls not as carefully (as I am often using a digital scale for weighing now vs. the RCBS 5-0-5, or just beginner casters luck. The other important variable may have been the fact the first lots I had cast were from lab grade lead (some my partner had had from past University of WI projects). Lesson learned to always double check the weights when changing an input.



I am believing that these balls will help even more with my 5x10 nickel sized hole quest.

Also, rob45...a batch is a poorly defined term that I share try to not use in references to calculation requests. i normally will check about 30 of 100 to see the heaviest and then set my scale a grain lighter and check for go no go and then split the group into heavy and light.

While the 1/2 grain variation maybe over kill for a RB, I will endevor to stick to it for my quest as it MAY not make a difference (or a very small one), but by doing it I will Know it is not impacting the accuracy.

Hornet... the after fill flow seemed the largest factor to get a consistent weight to what I had been doing.

I am also playing with heat treatments to .429 and .500 ww castings for 44 rem mags and 500 s&w's...but that is another quest :)

Thanks to all who took time to share. I sincerely appreciate your efforts on my behalf. :)

[KCSO]

If they are round, and shoot good it really doesn't make much difference. Now if 2 weigh 218 and 3 weigh 225 you might have problems.

[HORNET]

Glad to hear that it's working out well for you. It sounds like a LOT more consistent results than what you were getting. I assume that you meant .530-.529 on the diameters? That and a +/- 0.3 grain weight spread....doesn't get much better than that. You might want to check things out down in the Muzzleloader forum for info on patching & loading techniques that might help from here.
Note: The same overflow casting method will also help on your .44's and .50's.