Measure pellet head diameters to 0.01 mm accuracy

This from Ron Elbe, airgun author, and champion shooter:

I shoot 25 yard indoor benchrest matches with an Air Arms S400.   My favorite pellet is the 8.44 grain JSB Match Exact Diablo.  When I first began shooting, I used pellets straight from the tin.   I suffered too many inexplicable flyers.   So I began to weight-sort the pellets.   I found that weights typically varied by 0.4 to 0.6 grains in a tin.   By shooting only one weight of pellet at a time (and by disposing of the lightest and heaviest pellets) I reduced the flyers (but couldn’t eliminate them).   
Tonight I gaged 228 pellets that I had previously weight sorted to be 8.4 grains.  My results were as follows:
 
HEAD         QUANTITY
4.49       2
4.50       8
4.51       29
4.52       86
5.43       96
4.54       7
 
CONCLUSIONS:
1.     Even pellets that have been weight-sorted to exactly the same weight show significant variation in head diameters.  (So, sorting for head diameter is not redundant to weighing.)
2.    Sorting with the gage is somewhat time consuming.  But, it is FAR quicker, easier, and more repeatable than attempting to measure with calipers or micrometer.
3.    Initially, using the gage was somewhat “fiddly”.   I had to develop a technique to use the gage efficiently.   (Hint:  The pellet has to be exactly perpendicular to the gage in order to fall through.   That’s one of the reasons that setting the gage on its legs on the table is very helpful.)
4.    So far, I’ve only measured Diablo pellets.   I need to try the gage with wadcutter style pellets too.
5.    Based on my initial results, I intend to purchase the .22 PelletGage too.
 
The remaining question is whether or not sorting by head diameter will significantly reduce my group sizes.   Fortunately I have access to a 25 yard indoor range.   So I can test with minimal environmental influences.   Hopefully my schedule will allow me to test next week.   When I do, I’ll send you the results.

 
Thanks for designing and building a great tool.
 
Ron Elbe


And this from Cliff Tharp, publisher of Varmintair
Hi Jerry, I received my PelletGage a few hours ago, and all I can say is WOW!  What an eyeopener this tool is.  For example, my guns don't typically like pellets with a 5.50 MM head size.  The one exception has been the H&N Baracuda Green, tin alloy .22 cal pellet.  Several of my guns shoot them really, really well.  I was surprised, because the info on the tin says they are 5.50 MM.  Well, with the use of the PelletGage I just found out that the heads aren't 5.50 MM, they are actually a very consistent 5.53 MM.  That explains a lot about why they shoot so well.  Most of my guns do not like pellets with head diameters over 5.54 MM.  I've just discovered that the Predator Polymag, and Metalmag pellets that I have, and don't have much luck with accuracy wise, are too big to fit through the 5.55 aperture.  That may explain why my guns shoot them so poorly.  I've also been checking a bunch of other pellets as well, and have had a real eyeopening experience with some of those as well.  I am really happy that I bought this tool, and will be adding a .25 cal when they become available.  Now for some feedback.  I personally like the standoff legs.  The way that I use the tool, while sitting at a well lit table, having the legs on the unit is very helpful.  I ditched the plastic piece with the apertures in it.  I could not get the holes to center up over the size apertures in the stainless steel plate.  It was just in the way, and I find that I like to have direct access to the size apertures anyway.  I used the second picture frame piece on the back, to sandwich the stainless plate between that and the similar top piece.  It adds a bit of rigidness to the stainless steel plate, and looks very neat and professional.  It would work fine without the back plastic piece, but it sure looks nice with it.  So far, I haven't seen any need for apertures under 5.49 MM, but I do wish I had 5.56 MM.  Not a big deal really, but some of these pellets are running larger than 5.55 MM.  Again, thanks for a great product, and I look forward to getting a .25.  Hope this helps.