Blow forward

Blow forward is a firearm action where the propellant gas pressure and the friction of the bullet traveling down the bore drag the whole gun barrel forward to facilitate the opening of the breech.

[1] This forward barrel motion provides most of the energy required to eject a spent cartridge case and chamber a fresh round of ammunition, and contains a minimum of moving parts, and thus is more compact than other operating mechanisms of equal barrel length.

The vast majority of repeating firearms have their barrel fixed to the receiver or largely immobile in relation to the frame, with the breech face (as part of a moving bolt or slide) moving within the frame against the barrel.

Due to the reduced mass of rearward-traveling parts coupled with the increased mass of the forward moving parts (barrel in addition to bullet and propellant gasses), recoil energy is significantly greater than other operating mechanisms.

Most blow-forward guns rely partially on the inertia of the barrel as the rest of the firearm recoil away from it.