I've been wanting some sort of instrument/device to check muzzle velocity of my elderly Diana 15 air gun as I go through the various stages of restoration - the Diana was given to me as a 9th birthday present, it was already 2nd hand when I got it - my older brother and I would regularly go through 2 packs of 500 Marksman pellets on a weekend, when we ran out we'd dig some pellets out of the chicken shed wall - straighten them as best we could using our teeth and then shoot them again.


I gave some thought to a ballistics pendulum, then thought about possibly developing an arduino based chrono until I came across a HT-X3005 on Aliexpress - $34 delivered - in developing an arduino based chrono myself the cost of components alone would probably be double that.


The version I bought comes in 2 sizes - mine is the smaller version - comes with internal rechargable battery, instructions, cable ties, a velcro strap, brass spacers and a second end cap. The business end (end cap) has a series of numbered holes - the idea is that when the supplied brass spacers - 3 of - are screwed into the correct holes, the spacers form a sort of tunnel that will go over the muzzle end of the gun under test with the muzzle centered over the central hole through which the pellet/bullet passes, the 'tunnel' formed by the spacers can range from 20mm up to 30mm in 'diameter' to cater for different barrel sizes, cable ties or a velcro strap secure the instrument to the barrel - a bit agricultural but in practice probably works ok, a screwdriver is included as the end cap needs to be removed to attach the brass spacers, a second end cap is also included to cater for barrel sized sizes from 16mm, up to 40mm, also included is a bit of plastic tube which I assume is meant to go over the brass spacers possibly the protect the finish on the barrel.
How well does it work - so far yes, it does work - I haven't tried an actual gun as the package arrived rather late in the day but I couldn't resist blowing a 3/16 ball bearing through a small brass tube using the air line - the recorded 'muzzle' velocity was 61.6 meters per second or about 200 ft/sec

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