Air Gun Ballistics
Images taken with a high speed flash system based on the Mumford Time Machine to observe the rifling on a lead pellet fired from an air rifle.
The rifle is a Daystate Mk4 kindly modified by Daystate to give me a large level of control over the pellet velocity. The pellets are 0.177 Air Arms Diabolo Field.
The flashgun is being triggered by an IR beam across the muzzle of the rifle.
The following image is a crop from the previous photograph showing the rifling marks left on the pellet
These images are taken after a pellet was retrieved and shows the rifling on the pellet skirt and dome
Power and Pellet Deformation
The following image is of two pellets fired at differing power levels and velocities.
The left hand pellet was shot at 85 fps and the right hand pellet was at 780 fps.
The depth of the rifling has been significantly increased on the right hand pellet due to the skirt being expanded further into the barrel rifling. There is also a hint of deformation in the flat side of the skirt due to the increase in power or from the landing impact? In order to take the second shot at full power and retrieve an undamaged pellet I was shooting at a fluffy cushion over 250 yards away, eventually I managed to land a pellet on it 
it would of been a lot easier with ballistic gel. My thanks goes to a friend who was prepared to trudge up and down the field to check if I’d hit it because I didn’t have a clue!
I had also thought about filling a 4 inch piece of plastic pipe with water. One end has glued cap. Other end use plastic wrap and rubber band to hold water in pipe. Shoot through plastic kitchen wrap of course. You’d need several feet. Wrap probably only good for one shot. But plastic wrap and water are cheap, easy, and quick. Even grocery store gelatin gets expensive. Gelatin also requires quite a bit of prep. You could fill a 4 foot section of pipe with water in a few minutes.
I should add since I didn’t care about calibration, I reheated gelatin and reused it a number of times.
I was testing expansion of hollow point pellets. By and large you have to shoot hollow points faster than any rifle I have. I was admonished by an expert to think like a buffalo hunter. Expansion is a secondary factor. You first have to be able to hit a vital spot!
To recover the pellet you don’t need “real” ballistic gelatin. Use plain gelatin from grocery store, but make it extra concentrated – about 10 times what is used for regular gelatin. You can find details on web.
“Real” basaltic gelatin should also be calibrated with a BB to insure that the gelatin was prepared properly. Using water that is too hot weakens the gelatin structure.
Very nice and informative pics……congrats!!