Conjure lesser Sentry

You create a sentry 3 feet in diameter, and 5 feet tall. The sentry is a bronze cylinder with a half-sphere on top, the half sphere can swivel 360 degrees. A 2 inch barrel is attached to the half-sphere, witch can move up to the top of the sphere or down to where the half-sphere stops. Once you cast the spell, the sentry fires a small pebble at one target of your choice, +3 to hit, the target 2d4 + 1 bludgeoning damage on hit. For the next 3 minutes, you can cause the sentry to fire again for a bonus action. 

The Sentry has an Armour class of 16, and has 25 hit points. If destroyed, the turret implodes and every creature in a 5 foot radius has to make a dc12 dexterity saving throw or take 1d6 piercing damage from shrapnel. 

At Higher Levels The damage increases by 1d4 for every spell slot level after 2nd