mke one!!
As usual I am the dinosaur in the group....I made one bak in the 70's out of a newfangled "plastic" (cheep) set of calipers....((mine is vernier scale!!! today they are available in the dial version for abut 20 buks))...I took a 2in sq piece of pleiglass ((1/8" thick)) and scratched a mid line thru it ...then scratched a set of perpendicular stadia across it .224--.243--7mm and .308....then used crazy glue to attatch this see thru device to the back of the calipers...((I also drilled a lil hole in the stationary jaw of the calipers for a scratch awl from a tri-square!!! to keep it from moving as the sliding jaw is moved to measure the group))now with the calipers closed I set the one side of the stadia on one side of the group and open the calipers to touch the other side of the group...and "viola" the bullet dia.is automatacly subtracted and what they read is the aprox. group size....I have used them to measure targets that have been meas. at the range by experts with the best equip. and I am usually within .003 or .004"!!!........total cost 20 bucks,including the caliper....very simple ....close enuf for at home or on the range....you can tell if the groups are getting bigger or littler,,,and just toss it in the range box..where it will become one of your fave. tools....Roger
