Rifle-firable training grenade and rifle-grenade firing instruction system

Completely inert training grenade intended to be fired by means of a rifle and of a propellant cartridge, comprising a metal tube (1) equipped with a rear stabilizing tail unit (2) and with a front solid part (3) which closes off said tube, this front part (3) carrying a hollow nose (4) containing a marking substance (5), this nose (4) being fastened removably by engagement to the front solid part (3) of the tube, this nose (4) being sufficiently resistant to withstand the shot, but being destructible on impact, wherein the solid front part (3) of the tube is produced in one piece with this tube, the diameter of this part being substantially equal to or slightly larger than that of the rest of the tube, wherein the nose (4) engaged on this solid front part has an inner annular shoulder (11) bearing on the front surface (3a) of the solid part (3) of the tube, and wherein the front end of the nose (4) is flat, this nose (4) being shaped so that its wall can break in the event of its impact on the ground, the nose (4) having a wall possessing thinned zones (6), said thinned zones (6) consisting of grooves made on the surface of the wall of the nose, said grooves (6) extending in the longitudinal direction of the nose.