An adjustable buttstock clamp for a rifle is disclosed which includes a cam lever having a mechanical locking feature configured to engage with a groove in a buttstock extension shaft when in the locked position. A buttstock recoil pad may be attached to an extension shaft that can telescope in and out of the body of the buttstock, allowing the user to adjust the length of pull of the rifle and angle of the recoil pad. In one embodiment, the shaft includes a number of grooves on its surface along the length of the shaft and the shaft is held in place using a band clamp that is activated by the cam lever. When the cam lever is in the locked position, the locking feature engages with one of the grooves of the shaft to hold the buttstock recoil pad at the desired length and angle.