Before the appearance of assault rifles, the length of rifle bullets was generally more than 8 cm, and the volume and weight were too large. However, submachine gun is a kind of individual melee weapon with strong firepower between rifle and pistol, so there are strict restrictions on volume and recoil, so submachine gun uses pistol bullets.

Now, due to the widespread use of assault rifles, submachine guns have been marginalized and become individual self-defense weapons, and the requirements for volume and recoil are more demanding. So submachine guns have never used slimming rifles so far.