The Mk.4 was designed to replace the venerable Mk.3, to which soldiers complained was an unnecessary move. The soldiers complained that the rifle uses a round that is less likely to kill an enemy with a single shot and would rather use the heavier but more effective rifles they already have. The opinions of battle-hardened soldiers being trusted over those of government officials has stopped the rifle being issued as standard to troops.
The rifle has entered use with some security companies and foreign armies despite this.