How did PelletGage come about?
by Jerry Cupples

I’ve enjoyed shooting air rifles for a long time, and for the past couple of years, I have been learning how to shoot field target. It'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 of 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 them (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 it 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.

Do I really need this?

I have found variations of 40 microns in head diameter within one tin of European pellets. Perhaps more significantly, I measured a large sample of my favorite pellets, and found 90% of pellets from one tin to be 4.53. So, say we forget the 10% that could be less accurate than the main group - I was a lot more surprised to find another tin of the same .177 pellets that were gaged at a mean diameter of 4.51. Examination of the pellets at 40X confirmed this. They have a slightly different shape, a bigger head, and they are a little longer, too. The groups of the 4.51 head pellets were noticeably better in my rifle.

We have all suspected variation between two lots (or even two tins) of pellets. The PelletGage™ will quickly and simply confirm whether one important variant is present. It also serves to screen any pellet that is not round, or that has a parting seam.

If you would rather be confident that you know the diameter that works best for your gun, and be able to confirm each new purchase of pellets is consistent, you need this. Other methods on the market are more expensive, and more difficult to use.

Several airgun experts have evaluated prototypes of the PelletGage™, and they have all advised that this product should be brought to market. I trust you will agree.

Using PelletGage™

The PelletGage™ is a simple to use device to determine the head size of pellets in 0.01 mm (ten micron) increments.
There are five ranges, each has ten round apertures precisely cut into a thin metal sheet. These range as follows:

Cal     Range
.177    4.46 to 4.55 mm
.20     4.96 ro 5.05
.22     5.45 to 5.54
.25     6.31 to 6.40
.30     7.58 to 7.67

To use it, roll or drop the head of the pellet into the smallest expected aperture. If the pellet head is larger, it will not drop into the opening. Move up to the next larger size(s) - diameters are etched in the metal - and the pellet will drop partially through aperture, caught by the skirt. This establishes the size range of the pellet head as being between the largest aperture it won't clear, and the smallest that it will (commonly called a go/no-go).

The gage openings are cut through 0.008" type 304 SS sheet metal by a diode pumped fiber optic laser. The PelletGage can be used to rapidly sort pellets by head size, or simply to give you an accurate measure of the head diameter of that new tin of pellets you just received. Once you know what diameter your gun "likes", you can take steps to get that same diameter for better shooting results. You’ll be confident in that variable of the quest for accuracy.

Testing has shown significant size variation in tins of quality pellets. This may be a key to finding that next tin of pellets that shoots so well. It can also be used to check the diameter of pellets used to "slug" a barrel.

The PelletGage is more accurate, repeatable, and faster than using calipers or micrometers and is not as tedious to use.

The steel used is the tough alloy 304 - hot rolled sheet that has been cold rolled and annealed. It is durable, but should be used with care. Don't force anything through the opening, especially a hard material. Used with care, your gage will last for many years of checking lead pellets.