A new way to measure pellet head diameter

[JerryCup]

I’ve enjoyed shooting air rifles for a long time, and or the past couple of years, I have been learning how to shoot field target. I’s been a struggle, and my results were disappointing for quite a while. But, I met a lot of friends, and gradually improved. I learned a lot along the way, changing rifles, barrels, scopes, pellets, as well as trying to control my right index finger better.

My work in the electronics assembly business doesn’t seem relevant, but it was a prime factor. At one point, one of my new friends, Joe Peacock, brought a novel idea to one or our shoots. Joe is a very clever guy, and has several businesses. His “Speedy Pellet Inspector” is made from sheets of acrylic plastic, with laser cut holes to hold pellets so as to easily see and compare them and pick out any that are misshapen.

As it happens, one of my tasks at work involves designing and buying very precise laser cut tooling. The idea came to me that my tools made from steel foil would have the precision needed to gage pellets. I called my supplier (a very bright young man) and within a couple of days, we had the first prototype.

Measuring the diameter of a spheroid object isn’t easily done. Normal micrometers and calipers can measure one chord or section across the object, but you begin with an accuracy of about +/-0.0005 inches at best.

The .177 caliber pellets used for field target shooting are usually sourced in Europe and specified in metric units, such as 4.52 mm. So. we can buy ‘em (or we hope to) as 4.51/4.52/4.53 mm, etc.

Now, the 0.01 step is 10 microns, or 0.0004 inches. On a good day, holding your calipers perfectly you might be able to measure the difference between a 4.51 and a 4.52 pellet accurately, but you’d probably miss quite a few. So, if you sort on that basis, it’s quite possible that you mixed up some of both into your separated batches.

How is this tool made?

The best production method  for this tooling is a diode pumped fiber optic laser. Laser light is directed by a very fine optical fiber,  producing a tiny and well defined cutting beam. The accuracy and repeatability for the best of these machines is 2 microns, or 0.00008. So, if your machine is properly programmed and properly set, it will cut a perfectly round hole, easily stepping up that ten micron diameter for each aperture..

With a few trials to make the frame for this little gaging plate, we now have a tool with series of clean, perfectly round apertures stepping from 4.47 to 4.56 mm. After checking with a 40X optical comparator, they are “right on”. Note, the entire incremental span of all ten apertures is a 90 micron range, smallest to largest opening. That’s 0.0035 inches, or about the breadth of a human hair.

How is it used?

All of us who have gotten serious about airgun accuracy know that we have to find the pellet our gun “likes”. I think we are really selecting the exact pellet size to fit the bore of our guns.

The Pelletgage will allow us to know the diameter of the pellet’s head, and to make that determination quickly. It will also allow us to check that next new tin of pellets we open.

In use, most of us will find that we want our pellets to “go” on 4.52 and “no go” on 4.51, for instance (each rifle may differ). The version of Pelletgage being introduced has a plastic frame, and thanks to my friend Joe Peacock, a plastic guide plate with oversized openings aligned to each gage opening that helps the pellet head drop cleanly into the metal aperture. I’m confident in the quality of the materials and the precision machining of Pelletgage. This is a simple, durable and accurate way to be confident your pellets are the right size for your gun.

If you are interested, check out http://www.pelletgage.com