The Casting Void

[Zonie]

Everyone who has cast roundballs and many more that don't even cast them have heard about the infamous "casting void" or "bubble".

It forms right below the gate where the lead flows into the mold cavity.

It really isn't a "bubble". Rather, it is a void containing nothing but a pure vacuum.

It is caused by the lead flowing thru the gate, freezing, so the supply of lead to the cavity is shut off.

If the lead in the gate were to remain liquid as the newly cast ball was cooling, the shrinking ball would draw more lead into the mold thru the gate and be a solid casting without a void.

Usually, this does not happen.

More often than not, the lead in the gate freezes while the ball is trying to pull more lead in thru the gate. This results in a cavity filled with nothing at all. A vacuum.

A lot has been written about the need to position this casting void directly in line with the center of the bore.
Some say if this is not done, the ball may fly off in a unpredictable direction ruining the guns accuracy.

Testing has proven otherwise and I thought I might give my idea of an explanation for this.

In the world of physics, it is well known that a spinning object, if it is not restrained will spin around the objects center of gravity.

That is the place which has an equal amount of material or mass distributed around it in all directions.

Getting from the physics area into the real world of a cast ball, that center of gravity isn't far away from the actual center of the ball, even if there is a casting void.

Carrying this to the extreme, I've drawn a unusual case that could never really happen but it is about the worst case I could think of.

The cast void is so large that only half of the ball filled with lead!! :shocked2:

The remainder of the ball just has a thin skin on it that makes it look like a ball.



Notice, this drawing is to scale and the distance from the center of the ball to the center of gravity is correct for any ball that is cast with only half of the ball filled.

(The indicated center of gravity is based on the solid inner face meeting the thin shell in a sharp inside corner but I thought adding a fillet radius in that location would make it easier to see what I was trying to show.)

"OK. So the ball is spinning around the center of gravity. Doesn't that make the ball hit the target some place other than where the ball was aimed?"
Yes. It does.

"So, how far off of the place is the ball going to hit the target?"

The distance varies with the size of the ball but the answer in this worst case situation is, .375 X the ball's radius.

For a .50 caliber ball, the distance is .094" or 3/32 of an inch.

For voids smaller than my half ball, the amount of shift for the center of gravity because of the void would be less. Much less.

Before I sign off, yes, I know many of you have had "flyers" that were caused by something.
I'm only saying, they were caused by something other than the small cast void inside the ball being loaded in some unknown direction.

More likely, an errant shot due to a casting void is because of the different weight of the ball.
The bigger the void, the lighter the ball will be.

OK.
Now that I've stirred up the ant nest, I'll mosey on down the road. :grin:

 

[M. De Land]

:rotf: Mosey on down the rode indeed!
What we found to be true in long and mid range black powder cartridge shooting with lead bullets is that weight differentials really played havoc on the vertical dispersion and the longer the shot the more it effected it.
Most of us have learned to cast well enough to keep five hundred plus grain bullets with in a plus or minus weight variation of 1.5 grains.
That is .75 grains either side of zero.
In casting these I would say lube groove fill-out is more of a problem than voids under the sprue, in weight uniformity.

 

[Don Steele]

I'm one of those who frets over all the little things that go into making a good shot.
I most certainly won't shoot a ball that has not passed scrupulous inspection, and is withing 0.1 gn. of my targeted weight.
All that said, I thought this would be a good time to share an experience I had just this past Sunday.
I was at the range, shooting my 40 cal SMR when I had a "dry-ball". :redface: :cursing: Yea..I know...some of you never saw such a thing, but it does happen every now and then to those of us who are human.
I'm well prepared to resolve such a happening so it was no big deal to use a screw extractor type tool and pull the ball/patch outta my barrel.
After I got everything back in shape to continue shooting, I found myself staring at that ball with a great big ugly screw hole drilled into it. :shocked2:
Thinking..."What the heck"... I got a new patch, and loaded that same ball back into the rifle,over my normal 55 gn Goex 3f powder charge, big ugly screw hole "UP".
I had been shooting a steel pig silhouette,the body of which measures about 11" long (left to right) by 7" wide(top to bottom) offhand @ 50 yds so I took the shot with this gouged out ball, once again offhand, and darned if it didn't "ring the pig". :shake:
I don't plan to run a statistically valid test of gouged out balls...but this single experience does make one wonder. :hmm:

 

[Grumpa]

A hollow point roundball! :haha:

I have one of those sitting in the cellar. Now, I'll have to shoot it the next time out. I'll use paper, so I can see where it printed in relation to the "unmodified" balls. :grin:

Richard/Grumpa

 

[nhmoose]

op:

 

[Donny]

sounds logical... the bullet at light speed would not be affected, but when velocities slow way down this out of balance rears it head ? ?

 

[Don Steele]

I had a similar thought Richard.
I've read about some of the old time long hunters retrieving a ball from a deer and "chewing it round" to use again on another deer. Certainly wouldn't expect m.o.a. Precision out of one of these, but "minute of deer" might be feasible. I have to say I was pretty surprised that my pulled ball still hit that steel pig.

 

[ohio ramrod]

A hollow point roundball! :haha:

I have one of those sitting in the cellar. Now, I'll have to shoot it the next time out. I'll use paper, so I can see where it printed in relation to the "unmodified" balls. :grin:

Richard/Grumpa

Actually I have shot many "hollow point" round balls. I use a short "Aligning pin" in my short starter to center the hollow point . They really do a number on bambi And shoot as good of a group as solid round balls. :idunno:

 

[kingsax26]

well, I once owned a .32 rifle that I could never get a load worked. finally i started weighing the balls an kept all the same weights together....what an improvement. I no longer shoot small bore ...but ive yet to ever see an issue with my 20 bore guns. I dont think ive ever weighed 1 ball....they all shoot well enough for my needs just t he way they are

 

[Grumpa]

Finally got to the range on Wednesday. Loaded the previously pulled "ball" - it had a gaping hole most of the way through, and was imprinted with the rifling, which distorted it as well. Had to whack the starter with a hammer(!) to get the ball fully started, then some leaning into my steel ramrod got the ball seated.

At 50 yards, from the bench, the ball hit 9 1/2 inches low, and 3 1/2 inches to the right of where my previous shot had hit.

Bambi might have pranced away. An adversary would have dropped.

Can't draw any conclusions from one shot, and I don't intend dry balling enough to be able to shoot a test pattern with the recovered balls. :haha: Of course, we never intend to dry ball.

If the situation was dire, I would shoot a pulled ball as a last resort, and at as close range as I could manage.

Richard/Grumpa

 

[Billnpatti]

... the bullet at light speed would not be affected, .....

I have figured out how many grains it takes to get my ball up to the speed of sound but how many grains does it take to get it up to the speed of light? :idunno: :haha:

 

[nkbj]

... the bullet at light speed would not be affected, .....

I have figured out how many grains it takes to get my ball up to the speed of sound but how many grains does it take to get it up to the speed of light? :idunno: :haha:

May the FFg be with you, Billnpattiwan.

 

[Billnpatti]

May the FFg be with you, Billnpattiwan.

Ah yes, master......lube on, lube off. :haha:

 

[meanmike8665]

Being a bench rest shooter , or better yet trying to be a bench shooter a change of wind speed by 1 mph will move the ball more than a 3/32 of an inch. I can' t tell how my times I have seen someone miss a wind change and blame the gun, sights, ball, or shooting partner! A large void does not mean a terrible shot, but a missed wind change can and will ruin a good target. I weigh all balls and powder charges shot in bench matches and it does not mean all 50's. It is more about wind and light changes.
Michael

 

[Billnpatti]

Since messing up my left shoulder rotator cuff beyond repair and have lost a lot of range of motion and strength in my left arm, I have a difficult time supporting a rifle for shooting offhand. I would love to get into benchrest shooting but just can't afford a bench gun. I would have to sell several of my existing muzzleloading rifles to have the money and my kids won't let me do that. I built all of my rifles and they have been designated "family heirlooms" and cannot be sold. :idunno:

 

[Billnpatti]

As everyone who has spent any time casting bullets, I recently found some culls in my batch of .490 roundballs. They had been cast with a soft lead of unknown content. I was getting ready to develop a load for a rifle that I just completed. I was weighing out the balls into containers and my criteria was to divide them into groups within plus or minus 0.5 grains. As I was weighing them they were all falling into four groups of 174, 175, 176 and 177 grains each plus or minus 0.5 grains. Approximately 50% of the balls were in the 175 grain pile, approx. 30% were in the 174 grain pile, approx. 15 % were in the 176 grain pile and approx. 5% were in the 177 grain pile. However, in weighing a total of 207 balls, 4 were noticibley light. All weighed less than 170 grains. Upon examination, small holes opening into voids were noticed at the sprue. In culling these balls while casting, these voids were missed. I tossed these balls back into a pile to be re-cast. Strangely, I also found 3 balls that were way too heavy. These balls weighed over 180 grains. I have no explanation for this other than to say that they were obviously cast of a different alloy at some previous casting.

The take away from this is that no matter how experienced you are nor how careful you are in casting, variations in ball weight are inevitable. For this reason, it is necessary to weigh your balls and cull the bad balls to achieve maximum accuracy. Weighing criteria vary with different shooters. Some divide the balls into groups within plus or minus 0.1 grains and others divide them into groups within plus or minus 5.0 grains. My personal preference is to divide them into groups within plus or minus 0.5 grains.

 

[BrownBear]

My problem with voids is that I don't know where they are in a ball. Just no way to tell.

If you could locate them and center them on the center line (relative to the bore) each shot, they probably wouldn't have much effect at all.

No way to prove it (again, cuzz without xrays you couldn't spot them), but with the location of the void wandering all over the place in relation to the center of the bore, but intuition sezz it would affect accuracy.

 

[M. De Land]

I don't ever remember finding a void in a ball or bullet any where else but under the sprue.
Now you will find lube groove edges not filled out and if there is any thing that should unbalance a bullet it is that and yet even these hit end on and often will be well into the group center , which I cannot explain.

 

[LRB]

Same here MD. Right under the sprue. That is why it is wise to allow a generous puddle to form over the sprue when you cast a ball. Most often that will eliminate a void. At least in my experience.

 

[Zonie]

The point of making this topic was, even in a situation where 1/2 of a .50 caliber ball was totally hollow, the worst effect would be that the ball would rotate about a point that was only 3/32" off of sphere's true center.

That would make the hole it pokes into a target 3/32" off of hitting exactly where the gun was aimed when the bullet left the muzzle.

Of course, in the real world the void is much smaller than 1/2 of the ball in size so the effect of a cast void would be almost undetectable.

In other words, there are probably 25 different things that can cause the bullet or ball to be "off target" that will have a greater effect on accuracy than some tiny little void in a cast ball.