Mapping Pellet Trajectory

With the rain dampening all except spirits, I nipped out between cloudbursts to sling some lead.

Here's my lil experiment.

HW95k .177, AA Fields 8.3 grains, 764.8fps, Kneeling (because of the mud and the most used position when out), 19:45. (Click images to enlarge)

Pretty appalling shooting quite frankly. Certainly not the rifles fault. Haste and poor light for some of those 'groups'. I did still get two usable readings and a pretty good picture of what could be going on down range.

The 'constellations' are me trying to salvage something from the mess. turns out I was pretty close too. Chairgun has .0210 @ NTP and my reading was .0216 @NTP.

Keep in mind this is a rush job. I would advise that this be done with more care (and I intend to at the earliest opportunity). For the purposes of illustration, this has been useful. It can also serve a purpose for those who do not have, or refuse to get to grips with, Chairgun, and wish to find their optimum zero.

How to Calculate the Ballistic CoEfficient of your pellets.

As a follow on from my Self Reliant Airgunning - Pellet Production post , I thought I'd show a quick method on how I've been calculating BC without getting too technical.

The theory is pretty straightforward. I don't have two chrono's, just a combro, so I am relying on Chairgun and its 'BC based on POI difference' calculator.

Ten shots in total were fired. 5 at the zero of 12 yards, 5 at 30 yards. This gives us two distances. The fall of the shot will tell us how the pellet is performing in the barrel, then the air as it reaches its target. Of course, the chrono is telling us how fast it is leaving the muzzle.

Now, this is important. The database BC was very different from my findings. This is due to manufacturers taking an average performance figure, in the same way they take an average pellet weight and print it on the box. It's convenient and accurate enough for most peoples needs. Evidently, not mine!

When I was weighing the pellets I made, then a manufactured tin, I saw how we take so many figures for granted with out bothering to check and measure for ourselves. So no wonder we all have those 'mystery' shots that take us aback. Especially when changing pellet brand.

After the shots were fired, the average fps was taken (703.9 fps with a 10fps variation possibly due to a strip down just prior to the test) then the groups analysed and measured.

Accuracy on the bull would come later, for now, a clear grouping was sufficient. (I couldn't help but fiddle with the windage, though not elevation)

I settled for a rise of 0.896" over 18 yards. (click images to enlarge)

My old zero was 12.1 - 27.5 yards before the strip down and the RWS Supermags were calculated to be 0.0062 @ NTP already a big difference in performance (or calculations!)

Here we have the new zero and a graph that should accurately reflect the performance of my rifle and the pellet of choice. Chairgun will then update the pellet database for you with your BC calculation.

Yet another variable in airgunning to consider, measure and adapt to. Who said it was all 'point and shoot'?!

Self Reliant Airgunning - Pellet Production, Ballistic Co-Efficients

This evening I've undertaken some long overdue ballistic coefficient calculations on my "Tomahawk" Homemade pellets.

The results were interesting, though not exactly too encouraging. The pellets are a tight fit down the 97kt barrel as well as the Th208. However the .22's are very loose in my chums HW100! bizarre.

Thankfully accuracy was very good but range is limited with the 97 showing severe drop off over just 15 yards. Here are the chairgun results. (Click to Enlarge)

As you can see by the graphs, the drop off is most pronounced in the .177 through the HW97kt, I may perform further trials using the tx200 tomorrow out of curiosity. I've reported the findings to the chap who makes them to help him refine and modify his future products.

It doesn't help that both guns are still rather new. The 97 may benefit from a strip down, the TH208 from a tuning kit. My conclusion is therefore that these pellets at present are best suited to FAC rated air rifles. Though should the proverbial poop hit the fan I'd still be happy to sling these at some pigeons! Boy they would pack a punch i'm sure.