Vern juenke machine

alinwa said:
OK.

I'm just asking.

Anyone else understand eddy currents? My sum total experience with them has to do with sliding AL around on magnetized surfaces! Hardly relevant :)
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Seriously, what makes anyone think this machine induces an electric current in the test object? Should be easy to prove either way using a $10 Chinese multimeter. Everything I've read indicates this uses ultrasound. (Do the machines come with a warning about spinning live ammo?)

I haven't kept up with RF accuracy theory (hereabouts or elsewhere) but last I knew RF flyers were thought to be caused mostly by primer variability, rim thickness variability, and headspace issues. Do people still sort RF for rim thickness? Do people sort RF ammo for weight or bullet runout (if that's even practical to do)?

PS Suppose eddy currents were induced by moving ammo in a magnetic field of a strength likely to be encountered on your bench. Such currents would be so small as to be insignificant WRT any inductance heating. How hot does a primer need to be before it discharges? Think you could readily heat RF ammo that much using magnets? Think about it..

Brian
 
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I believe that the magnetic damping systems that are built into balance reloading scales work on the principal of eddy currents. How would you hook up a multimeter to prove or disprove this? Have you looked at the published schematic of a Juenke machine? Also, for some time there has been a tool available to measure the straightness of rimfire ammo, a friend made one of his own, and found that straighter rounds shot smaller groups. I do agree that it seems unlikely that enough energy would be imparted to a rimfire round to set off its primer.
 
It was darker than night.
I used some Midas ammo from about 1994
The wax was dried up to white powder so I just wiped it off.
We'll that did no work.
 
We stated this machine measures thickness of jackets or how the lead is connected to the Jacket and so forth.
This is a test I would like you to try. Find two bullets exactly the same maker and type just deferent lot.
Using ogive checker check the ogive to base and make sure they're different. Which happens a lot when there's a difference in lot of bullets. Spin them and look at the difference that it picks up into two bullets.
It's not picking up any kind of thickness difference,it's not picking up lead separation.
It's picking up the difference in distance from ogive to base. I say because it shows the difference of distance from sensor to bullet. What do you think. We on the same page on this.
 
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Lou Murdica said:
This is a test I would like you to try. Find two bullets exactly the same maker and type just deferent lot.

Using ogive checker check the ogive to base and make sure they're different. Which happens a lot when there's a difference in lot of bullets. Spin them It's picking up the difference in distance from ogive to base. I say because it shows the difference of distance from sensor bullet. What do you think. We on the same page on this.
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Lou I have taken two bullets from the same die from two of the top makers, twice. They even have different null points from box to box on the Jeunke meter!!
Dunno??
 
Exactly what are you trying to determine?

I lost track somewhere:)

What are you trying to determine?
 
I believe that the question is what exactly does the Juenke machine measure and how does it work? One thing that was interesting to me was the post that reported that if a box of bullets were dropped on the floor, that the readings would increase significantly. So, among other possibilities, it would seem that one thing that is measured is how round bullets are. Years back, a friend who is a bullet maker, and whose bullets are still highly sought after, sent me some samples of some flat base bullets that were suitable for for my PPC. Since we had been discussing how to get the most accurate measurements of bullets, out of curiosity, I set my micrometer to where I got what felt like about the right feel of drag on the pressure ring, then to check myself, I picked up the bullet and did it again. The second time it felt looser. Thinking about it a bit, I did several checks slightly rotating the bullet, and decided that for whatever reason that it was very slightly oval. They shot just fine, and I decided that 60K+psi would probably straighten out any little difference that existed before ignition. Perhaps not all inconsistencies that can be measured will actually show up on the target.
 
For me it definitely sounds like Eddie currents and if so, in my opinion, it is not easy to exactly say what it is measuring just by looking at the meter... Eddie currents is quite complex, it depends on material, thickness, cracks, contact etc. and therefor I think (without setting up complete equations) that the only thing you can say is that if the meter is changing them there are difference between the bullets, no more no les!

My 2 cents...
 
-Markus- said:
... if the meter is changing them there are difference between the bullets, no more no les!
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Yes, this sums it up pretty well. Eddie current paths radiate from the source to the sink like the layers of an onion. Anything conductive in the voltage potential field affects the paths and the net current that drives the meter. Roundness, length, shape, jacket thickness, core size, voids in the core … everything. It measures everything all together, so it is not impossible with this meter alone to isolate one thing that is different between two bullets. One bullet could be oval and another have a thin spot in the jacket and they could read the same. Or you could have counter-balancing defects that cause the bullet to read as perfect.
 
I understand more than i did . But an electrical engeneer i'll never be.

I had this juenke thing here for over 20 years, only ever used it to check bullets
myself or al weaver made. either we made good bullets or never knew how to use the machine.
about 2 weeks ago, I ran some 25cal, 100gr sierra match king bullets through .
I have an extremely accurate 25-06 and i'm here to tell you i could pick out the good from the bad,
and i mean to the extrem. for normal chuck hunting or position shooting they were plenty good,
but off the bench , all of a sudden the fliers were gone and it is almost like shooting custom bullets.
out of 200, I culled out 36. they will be used for varmints.
when this thread started I was going to sell the Juenke , but think i'll hang on to it for a while.
Ken
 
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