The Russian Mosin Nagant Forum

When i set the gas valve to single shot/grenade launcher mode and fire a shot, the bolt still starts to unlock but doesn't complete the unlocking process, the upper half can be pushed forward again and click back into place after the shot.

is this normal? could my ammo be too hot? could the locking mechanism be weak?

Good to go.

Of course, your action is principally set up for gas operated cycling. But when you eliminate the piston/operating rod from the mix, the bolt is still resting only against a beveled rear lock-down lug. The blowback will cause the bolt to tilt upward in the rear, but won't go any further, since the carrier has no rearward force.

What you are feeling when you push forward is the bolt tilting back down against the rear lock-down lug.

Martin is very correct! What you are seeing is the normal operation of the rifle in the single shot mode.
Shoot and enjoy.