Compression projectile \Com*pres"sion pro*jec"tile\
A projectile constructed so as to take the grooves of a rifle
by means of a soft copper band firmly attached near its base
or, formerly, by means of an envelope of soft metal. In small
arms the modern projectile, having a soft core and harder
jacket, is subjected to compression throughout the entire
cylindrical part.
[Webster 1913 Suppl.]