An apparatus for measuring a projectiles transverse displacement at {HEAD ~ muzzle exit} of {TAIL ~ a gun tube} which comprises: 
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An apparatus for measuring a projectiles transverse displacement at { HEAD ~ muzzle exit } of { TAIL ~ a gun tube } which comprises :
OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH