Odd Topic - Bullet Balance Tester

An odd thought pops in now and then, as some may have noticed, and I'd like some comments on this one:

Most of us are familiar with the bubble balancer for tires that used to be used before the spin type balancers became popular.  Has anyone ever thought of or possibly pursued a similar device to check cast bullets?  What I'm envisioning is a balanced device upon which a bullet is placed, that would detect whether the center axis of the bullet was also the center of gravity.  The bullet holder would need to be constructed such that the bullet was truly centered and of course this would be prior to any lube.  It would also need to be capable of doing a pretty instant check to be of real value.  I'm thinking that it should be capable of detecting a .5 grain volume void off center in a 185 grain bullet.

Obviously, a spin test would be more precise, but much slower.  If a small balance checker was avilable would anyone check bullets with it?  Could such a device be used to check freshly cast bullets, so that inferior ones could be put back in the pot?

Has anyone ever explored this or maybe even developed something along this line?

These folks make one for jacketed bullets.http://www.bulletdoctor.com. this was invented by an old rifle gunsmith named Vern Juenke.  For cast bullets you'd have to use ultrasonics which would require a video display and much different circuitry.  But if you had an ultrasonic tester it could be adapted.

I think there would be a problem testing lead with ultra sound. The system uses sound propagation thru the material and a reflection off a void. I would think lead my not be a material that can be tested that way. Can find out if anyone is interested.

I didn't think you benchrest shooters shot cast lead bullets 

This chart suggests that you could use an eddy current check for identify voids or flaws: http://eddy-current.com/conductivity-of-metals-sorted-by-resistivity/

Eddy Current testing:
http://joe.buckley.net/papers/eddyc.pdf
http://en.wikipedia.org/wiki/Eddy-current_testing

I don't know if I want to test my bullets, shooting perfect bullets will foil my excuse for the lousy shots on the target being caused by a void in the bullets.

I'm not sure eddy current would work as there may be too much conductivity.  Ultrasound is used for crack and void detection in aluminum billets so that is why it was suggested.  However, all that said, if the cast bullets have voids then the casting process is wrong.  Spinning bullets in a tester won't fix that process error.

Sounds like a interesting idea but imo its overkill for 45 bullets .A simple weigh test will separate out the bad bullets, Several of my friends shoot a 160 lswc, these are very accurate, to be the most accurate we weigh them, Its easy to tell  if one is  good
by weight, a fully formed head with even lube weighs 163 +- .5 these will drill the x ring at 50 yds all day out of a good gun.

An easy test is to roll the bullet down a metal ramp. If it rolls smoothly, it is (supposedly?) better than one that sounds rough. This assumes no wax or similar bumps on the bullet.

I would thing that the rpm developed as it's rolling down a ramp will be no where near the rpm developed as it exits the barrel. A 45 bullet will spin at about 36,000 rpm out of a 1 in 16 barrel if the velocity is 800'/sec.

As David said, weigh them, segregate them, and use the heaviest for accuracy.

Froneck wrote:I would thing that the rpm developed as it's rolling down a ramp will be no where near the rpm developed as it exits the barrel. A 45 bullet will spin at about 36,000 rpm out of a 1 in 16 barrel if the velocity is 800'/sec.

If I did my math right...
That .45 bullet would have rotated 114 revolutions from muzzle to 50yd target ?

Clarence

C.Perkins wrote:

Froneck wrote:I would thing that the rpm developed as it's rolling down a ramp will be no where near the rpm developed as it exits the barrel. A 45 bullet will spin at about 36,000 rpm out of a 1 in 16 barrel if the velocity is 800'/sec.

If I did my math right...
That .45 bullet would have rotated 114 revolutions from muzzle to 50yd target ?

Clarence

I get 112.5 revolutions to 50 yards but you are both essentially in agreement with your calculations.

36,000 rpm for 1/320th of a second = 112.5 revolutions to travel 50 yards at 800'/second.

Now what?


Bruce

I would just weigh and segregate them as mentioned above.

Went to just shooting jacketed only so I quit doing that.

Clarence

Not Much Bruce, Just that the roll test would not be a very good test. The number of turns the bullet would make will have to include the slowing down of rotation and the slowing down of velocity but I assume that the exact number of rotations is within the needed margin of error for this thread.
 When using purchased cast bullets those that were rejected were used for practice, I was surprised to see how well some shot and how bad some that were not off weight as much did. I would think that it's the location of the void that causes the most error.
 When Adam started winning matches we switched to Jacketed.

Froneck wrote:Not Much Bruce, Just that the roll test would not be a very good test. The number of turns the bullet would make will have to include the slowing down of rotation and the slowing down of velocity but I assume that the exact number of rotations is within the needed margin of error for this thread.
 When using purchased cast bullets those that were rejected were used for practice, I was surprised to see how well some shot and how bad some that were not off weight as much did. I would think that it's the location of the void that causes the most error.
 When Adam started winning matches we switched to Jacketed.

Not to nit pick, but I doubt the bullet rotation slows very much.  Velocity slows for sure.

Well I really wouldn't know but the rotation has nothing to sustain it. I would agree that the velocity will probably drop at a greater amount air to air pressure but I can't say what will effect rotation speed. I would say it slows but to what degree I have no idea and to lazy to research it.