This feature story is brought to you courtesy of Orion Scoring Systems.
Competition Air Rifle Pellets are all the same and interchangeable….right? Not exactly!
This sport’s equipment (Precision and Sporter class air rifle) share the use of the same common diameter of soft lead pellets, but even among the same model of rifle from the same manufacturer, different pellet sizes may be preferred between two rifles. You probably already know that competition airguns are .177 caliber (177 thousandths of an inch). The metric equivalent is 4.5mm. What you may not know is that these .177in/4.5mm pellets are made in different sizes as a way to refine accuracy and match characteristics of your rifle’s barrel. These different sizes appear as different head sizes. They typically range from 4.48 and go through 4.49, 4.50, 4.51 and 4.52. With 4.50 being the most common. These sizes are determined by the different molds used in manufacturing. Further, variances in lead chemistry and mixture quality may cause the rifle to shoot at higher or lower velocities causing higher or lower shot groups to form. Also, variances in weight of the pellet may cause changes to velocity and therefore shot impacts on target.
Well, can’t you just pull out the test target that came with the rifle? While that is a live sample of 5 shots fired through the rifle, that only confirms that the manufacturing process was successful and the next stop is a packing box, it does not tell you the optimal size, brand, or weight characteristics that is unique to that rifle.
Every time there is a change in the manufacturing process – Operator shift change, lead wire spool runs out and needs to be replaced, a machine malfunction, a tweak to a machine setting, this necessitates a new lot number. Lot numbers are usually shown on a sticker on the bottom of a tin of pellets or sometimes on a card in the cover of the plastic tray. This sticker may also contain info like the date a lot was made, we are really just concerned with the sequential numbers known as “lot”. Each manufacturer uses their own system, so comparison isn’t valuable but it will tell you (through testing) which one your rifle prefers.
How do you determine which size/brand/weight/lot is best for your rifle? Lot – level Pellet testing.
There are two ways you can perform lot testing – using paper targets or using electronic targets. Orion can help with either method.
Steps to testing using Orion:
- Gather as many unique lots you have on hand or choose to acquire.
- Create a local match and add your team members as an easy way to remember who’s who while recording data.
- Secure your rifle to a steady a vise in order to remove the human element of variation in holds/process/etc. Make sure to begin with a full air cylinder
- Hang a paper Orion target or use your Athena, Sius or Megalink electronic scoring targets (don’t forget to link your match to the EST)
- Change your EST to record fire from sighters.
- Optionally, have a chronograph on hand to record muzzle velocities by lot as well to insure consistency.
- Confirm that your rifle in the vise is pointed safely at the target and will make contact somewhere within the scoring area.
- While keeping a log, record the lot number and fire 10 shots without disturbing the rifle in the vise. Be gentle loading the subsequent pellet. It is important to do this in a systematic way and shoot lot 1 first, lot 2 next, etc with each rifle in the same order. Repeat until you have 10 shots for each lot per rifle.(You may need to change targets after each 5 if using paper).
- Do not concern yourself with score and do not adjust sights. You are looking for group size only
- When complete, go to the match results tab in Orion and print Individual score sheets.
- I know that the first 10 shots were lot 1 for each shooter, next was lot 2, etc.
- Create a spreadsheet or paper log of the best (smallest) groups for each rifle, be sure to include 2nd 3rd and 4th best as well as these are depleting assets and once used, are almost impossible to find the same lot unless purchased at the same time.
In this example, I tested 5 lots from 3 manufacturers in different head sizes using 4 different cadet’s rifles on an EST. Analyzing the results, I look at group area (shown under each 10 shot series). This is a statistical measure using bivariate normal distribution. In more human terms, what the group area means is 90% of an athlete’s shots landed within this distribution. Some of you may have experience with other forms of pellet testing where the outside diameter of the two most disparate shots out of 10 are measured, the method Orion utilizes, considers all 10 shots rather than just 2 of 10.
What you are looking for in either method is much like a golf score….the lower the better!
I have our cadets perform pellet testing about once a year. It builds their confidence knowing they have a pellet that performs well in their rifle and helps coaches have an excuse eliminator if a shooter tries to blame their equipment for a lousy shot process on a particular day!