Author Topic: How to determine a roundball moulds casting weight?  (Read 3698 times)

Offline rick landes

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How to determine a roundball moulds casting weight?
« on: February 15, 2010, 06:27:02 PM »
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.
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Offline Kermit

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Offline SCLoyalist

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Re: How to determine a roundball moulds casting weight?
« Reply #2 on: February 15, 2010, 07:55:22 PM »
Another useful site about muzzleloading numbers is   http://members.aye.net/~bspen/math.html

The volume of a sphere of lead, in grains, can be determined by multiplying 1503 by the diameter cubed.   In the case of a .530 RB,   .53 X .53 X .53 X1503 = 223.7 grains

How much the sprue adds would vary from  mold to mold (but not from cast to cast out of the same mold) so might add a grain or two to your average. 

As long as your casting practices don't introduce bubbles or voids in the ball (which would be evidenced by occaisional  lightweight balls a couple of grains below average), you should be in good shape.


Offline rick landes

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Re: How to determine a roundball moulds casting weight?
« Reply #3 on: February 15, 2010, 08:06:39 PM »
Thanks guys!
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Offline Bill of the 45th

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Re: How to determine a roundball moulds casting weight?
« Reply #4 on: February 15, 2010, 08:35:48 PM »
Rick, another consideration is the true diameter.  Is your .530 really that diameter, or slightly under, or worse oval.    A .529 or 28 will cast around the weight you are getting.  The cherries that are used will wear, and cause a smaller diameter to be cast.

Bill
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Daryl

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Re: How to determine a roundball moulds casting weight?
« Reply #5 on: February 15, 2010, 10:29:15 PM »
Rick, another consideration is the true diameter.  Is your .530 really that diameter, or slightly under, or worse oval.    A .529 or 28 will cast around the weight you are getting.  The cherries that are used will wear, and cause a smaller diameter to be cast.

Bill

Bill hit an important aspect of casting balls from production moulds.  Not all moulds and actually few indeed cast at the diameter they are supposed to.

Exact size does not matter. For match shooting, you need to shoot as large a ball as possible, yet still allow you to load with the rifle's rod. (or range rod if shooting bench, etc.)

Consistancy is the rule in black powder shooting. Everything must be done exactly the same, shot to shot. Actual shooting is less than 50% of the accuracy component in this game.

Using balls within .5gr. is a good start. I am assuming square bottomed or grooves of the actual radius of the bore.  Therefore a .54 should be shooting at least a .535" ball, not the smaller .530". Deeper grooves, like .020" or deeper might require a .530" ball and a sail canvas patc to fill.

Watch your patches to see they are perfect, no cuts, no burns.

Offline rick landes

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Re: How to determine a roundball moulds casting weight?
« Reply #6 on: February 15, 2010, 10:44:08 PM »
I am shooting a Rice barrel (swamped .54) and using the .530 they are recommending. I am currently using various compressed and measured by micrometer patches so as to control that variable.

I do not have my notes here, but I believe I am using a patch that compressed is .0125 or .0130, at normal, read uncompressed these are .023 thick. It is basically a tough denim material.

It shows no fray or burn through with this combination over a 85 grain FFF Geox load.

I am hoping to get the balls under control and I will check them for concentricity and diameter. I have not mic'ed the grooves of the barrel as of yet.
“No free man shall ever be de-barred the use of arms. The strongest reason for the people to retain their right to keep and bear arms is as a last resort to protect themselves against tyranny in government." Thomas Jefferson

Offline rick landes

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Re: How to determine a roundball moulds casting weight?
« Reply #7 on: February 16, 2010, 05:51:17 PM »
Rick, another consideration is the true diameter.  Is your .530 really that diameter, or slightly under, or worse oval.    A .529 or 28 will cast around the weight you are getting.  The cherries that are used will wear, and cause a smaller diameter to be cast.

Bill

My casting efforts last eve were very successful. I poured at 700 degrees F 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.

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.
“No free man shall ever be de-barred the use of arms. The strongest reason for the people to retain their right to keep and bear arms is as a last resort to protect themselves against tyranny in government." Thomas Jefferson