Hello, all,
The Pelletgage plates are cut on a bed-type diode pumped fiber optic laser. The beam is also focused with a condensing lens to minimize the kerf. The (very expensive) machine that does this is optimized for cutting thin sheets of metal, and focused/setup to cut 0.2 mm thickness stainless steel - an alloy with very fine grain that has been hot rolled, then cold rolled and annealed. Both the metal sheets and the specialized machine permit far more accuracy than a typical industrial laser or plasma cutter. It requires a rather long (and expensive) time on the laser to cut apertures and engrave the diameters on the sheets.
Quality diabolo airgun pellets have been sold for many years with 0.01 mm increments, i.e. 4.50, 4.51, I'm told that criticality is often some minimum or maximum head size in which case, going above or below that point causes bigger groups. It is sometimes a matter of too much head size variance within a tin of pellets, as well. I also believe that the head size of slugs is more critical than diabolo pellets.
That 0.01 mm increment of nominal pellet sizes sold today is 0.0004 inches. Although this is a tiny change in diameter, it does make a difference in many guns, and the pellets DO vary much more than this, either due to manufacturing tooling or to undesired variances. I have always advised that checking and/or sorting pellets is only of value if your equipment and skills are somewhat advanced - it may be useless if shooting cheaper pellets from a big box store rifle, but it will have real value for competitive shooters and hunters using good equipment.
The apertures on all Pelletgages are verified during setup by my supplier (and again by me at receipt) using Class X Plug gages, These are NIST traceable and accurate to +0.001/-zero mm (+0.00004/-zero inches). My sets (Metric X PPM25) have 25 gages in steps of 0.0025 mm (0.0001 inch). I'd suggest anyone who needs to positively find the width/diameter of a slot or aperture should get a set (they are also sold individually) to check this. Delltronic is a good company, although they only sell through regional distributors - depending on your location.
https://www.deltronic.com/literature/Deltronic-Gage-Guide-2014.pdf Pelletgage apertures are guaranteed to be 0.0025 mm of nominal. Typically, a plug gage inserted into the same nominal size apertures enters with an interference fit, and it is impossible to insert the 4.5225 plug into a 4.52 aperture, while the 4.5175 plug slides in easily.
It might be interesting to see a specified and guaranteed rifle bore tolerance and guarantee, or similarly,
for pellets. Unfortunately, I don't see that yet.
regards,
Jerry
“I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meagre and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely in your thoughts advanced to the state of Science, whatever the matter may be.” Lord Kelvin, 1883
"Head size matters." Jerry Cupples, 2015
