Pellet testing of the modified Crosman 2250b, goal is to find a pellet that has a good FPE and groups well. This is using an H&N Sampler pack and some other pellets I have acquired over the time.
Speed and FPE Testing
Using this diagram I found for a homemade chronograph that using parts bought from China for less than NZ$10 I have a working chronograph. From reading comments people have tested against a commercial chronograph and the results were with 1% of each other. It is based on using apps (I used that used SoftChrono and the download is available here.) sound to measure the time it takes for the pellet to travel a known distance. By using light instead of sound it should be more accurate as long as the pellet passes through the light beam.
The PVC pipe I have is 50 mm internal and lining the rifle up works OK. I would not want to try to use this with a powder burner or anything other than muzzle velocity as the chances of hitting it are pretty high and needing the laptop nearby.
The testing procedure was to run a string of 3 shots per pellet allowing enough time for the gun to warm up again and take the average of these shots to give the muzzle velocity. I decided to run 3 as with the sample pack of pellets I did not want to use too many doing this before a chance to group them.
Due to the variance of the levels received from the IR receivers the automatic FPS reading from the software was not always accurate but using the analysis feature it is quite clear to see where the peaks are of the pellets passing through. The screenshot below shows these peaks and knowing the speed should be around 450 fps for the heavier pellet.
The results are below in the table, after some issues of the speeds being very low I found the CO2 was leaking from the o-ring on the tank after it had fallen apart. The speeds are now where I expected them with the sweet spot being the 18-grain pellets.
I only ended up using one shot as I had used a few in the previous runs.
After this testing and with the bulk fill done I am going to send it back to Minte to do some more work and see what further gains are available now that shot count won’t be an issue. At the same time will also get an HPA tank and regulator and get set up for compressed air as well CO2.
I have included the ballistic coefficient to be able to use a trajectory calculator to give a good guide to how each pellet should perform.