Question to 'Vern Junke Internal Concentricity Comparator' owners. Has anyone compared the accuracy using "junk" standard projectiles (greater than 15 deviation units) compared with "hummer" standard projectiles" (less than 5 deviation units) using exactly the same brass with all other variables kept to a minimum (that includes case neck concentricity, neck thickness, powder weights, etc).
Yes, that has been done time and time again. That is why you have many of the top guys using the Juenkes. Most will sort to 3 deviation units.
Each machine is slightly different. I keep a round or case for each caliber and bullet in small tubes their inital DU markings on them. That way it is easy to re zero the machine to that bullet and readings.
You will find that many competitors number each case and sort by DU. If you are firing at a range with pits, the pit crew marks on a plotting sheet the location of each round. So it is relatively easy to see which case threw a round out. That is how we learned to use the Juenke for cases and I have watched the same case "throw" a round out of the group three times in a row before it was discarded.
The Hoover family in PA sorts cases by chrono readings and has won more matches that anyone else remotely being close.
Most will anneal cases every 2-3 firings, seat with arbor presses by "feel" or with a dial indicator for pressure on top. They always check runout and only .001 or less will make a match round.
Anyone can fire a tight group once in a blue moon and post about their gun shooting in the .2s. However, most cannot do it back to back. Consistency of all variables is the key.
I do not use the Juenke on BIB bullets or Clinch Rivers, but I do sort by ogive just for comfort sake, even though they are normally max variance of .003 or less.
The Juenke seems to be able to allow you to sort cases by Deviation Units (DU. As I said, I have seen the same case that weighs exactly the same to .010, lenght, same lot etc throw a round out of a group three times in a row. When that case was put on a Juenke, it was about 12-13 DUs from the othes in that string.
I only measure bullets on a Juenke. It shows bullet jacket thickness variance, and sometimes internal voids. I use a Buhay bullet comparator for dimension checks.
In my view, it's valuable for identifying bullets with internal flaws. Thats it.
But as Bountyhunter said, w/regard to precision shooting, high deviation bullets really do depart from low DU bullets.
While I have no doubt DUs might indicate higher on flyer causing, crappy CASES measured on it, there are better tools for brass:
H20 capacity checks for variance in volume.
A neck mic for thickness variance.
A concentricity gauge for runout.
I would think anyone competing would use these tools anyway.
But I don't compete, so don't know for sure.
You are correct, we always use the neck mikes and neck turn normally. We always check runout too and the dies are set up to minimize that to begin with. Neck tension is tightly controlled and annealing is the norm.
The Juenke IMO spots variances a lot easier and more accurately than the H20 way.
Each has his own "black magic" system of reloading that he/she is comfortable with.