Cast Round Ball and Density Info

[gitano]

I posted this info in a thread in the Black Powder/Muzzle Loading site, but I thought I'd post it here too as it pertains specifically to casting.

Yesterday I cast some 19 RBs from the brass mould I got from England. The mould was spec'd to cast a ball 0.620" in diameter. Of those 19, I chose 12 that were the most consistently filled out. The average weight was 343 grains with a spread of 3.4 grains, almost exactly 1%. In my limited experience, that's pretty good for cast bullets from wheel weights.

They looked pretty good, but when I put a mic on 'em, I was a bit disappointed. They were consistently out of round by about 0.0055". Across the seam they mic'd at about 0.614". 90 degrees from that they were fairly consistently 0.619". The max spread was 0.0035" for the large dimension and 0.0026" for the small dimension (5.6% and 5.7% respectively).

I am not yet too concerned about this for a couple of reasons. First, I don't yet know how they may shoot. For all I know, they may be the perfect match for this bore. Second, this is a smoothbore pistol. I don't intend to push it past 50 yards, and my expectations are relatively low with respect to precision. Nonetheless, I will be contacting the machinist that made them and letting him know. Not to poke a finger in his eye, but to give him feedback on his manufacturing procedures.

Since these are spheres, and I had precise weights and dimensions, I could calculate the density of my wheelweight alloy. That's difficult to do with a cast "bullet". Strangely, the figure came out to be 11.062 grams per cubic centimeter. "Strange" because the density of pure lead is 11.34 g/cc. That means that the wheelweights I am using are very nearly pure lead.

Because of the above, I decided to mic the nominal 0.600" Lee RBs and see how round they were and check the density of that batch of alloy.

They weighed on average 321 grains. The spread across five balls was 0.97 grains or 0.3%. They all mic'd between 0.604" and 0.605". A little large - 0.005" - but very consistent. No particular difference between the dimension on the seam or 90 degrees off. In other words they were within 0.001" of 'perfectly' round. I also checked the density, and came up with 11.011 g/cc, which again is very close to pure lead.

Paul

[recoil junky]

Round things like sphere's are pretty hard to machine. So I've been told. I guess I never worried about round balls being round, I just shot them.

Also I've found that cast bullets (at least mine) aren't "round" either. My 429421's are a bit "egg shaped". I can tell this by the way they come out of the #45 sizer/lubricator. They shoot better than I can, so I'm not concerned about them either. Dad told me "That's why you size bullets, to make them round."

 But now you've got my curiosity up so now I 'll go and measure everything to see how "out of round" everything I cast actually is.

Like you, if I get wheel weights to cast within 1-2% of actual I'm plum tickled.

RJ

[gitano]

Have a look here http://thehunterslife.com/forums/showthread.php?p=106963#post106963 for a target I shot at 15 yards with the .620s.

I have always been in agreement with the idea of "That's why you size them". However, I don't have a round ball "sizer".

Paul

[HSM_miner]

I like to size my round ball while pushing them down my barrel.  Close to pure lead, so they deform easily anyways.

[recoil junky]

As long as they are "balanced" I don't think it matters. You know, no voids an' such. I've come to notice that even the sprue doesn't affect ball flight all that much. I always try to load them so it's on top though.

The bigger the round ball, the smaller the sprue, so the less affect it would have. Some shooters I used to go to Rondyvooz with would trim the sprue off and make the ball round so's it'd shoot better. I could never tell the difference.

RJ

[gitano]

I always try to load them so it's on top though

I've read and heard that as the common wisdom. Of course I had to think about it, and when I did, I decided that sprue-down was how I was going to go. The reason being, that whatever the effect of the sprue, one could be CERTAIN it has the most effect by sticking it right out front where it is CERTAIN to contact the air at the front of the ball as it travels downrange. If it is in the rear, the turbulence at the rear of the ball will be WAY more significant than whatever slight influence the sprue stub would have.

When shooting a RB from a smoothbore, you're essentially throwing a "knuckleball" downrange. As those familiar with baseball know, a knuckleball "wanders around" and its final location is unpredictable. The reason ballistically, is that as the ball pushes its way along, the air slips by it in a non-uniform way. First to one side then the other. The flow is random. With the sprue stub "leading the charge", the sprue stub can actually influence that flow considerably. If it's in the back, its potential influence is considerably less.

I've read that the reason to put the sprue stub forward is so that it can be placed "consistently". That's certainly true, but I feel confident that I can place the sprue stub just as consistently "down" as I can "up". I also don't think it matters much at all whether you put the sprue stub up or down if you are shooting RB from a rifled barrel.

Paul

[recoil junky]

Having no 'sperience with shooting smooth bores, I agree with the knuckle ball theory.

My TC Hawken shot round balls amazingly well, but shot Lee's target minnie with amazing accuracy. Of course my eyes were 30 years younger at the time. And sadly (or stupidly) I traded the Hawken for something else which I no longer have.

RJ