Marbles Bullseye Rear Barrel Gun Sight Fixed SIght .22 (NO Elevator Adjustment). The Marbles Bullseye sight is misaligned, the front sight drifts out of the center ring, signaling the shooter to cheek the stock and make correction. It's instantaneous, obvious and fool proof-the Bullseye does this the same way peep sights naturally center the front bead in the aperture, but automatically. Teaming the Bullseye with one of Marble Arms (c) front bead sights makes it double easy to stay dead on in any shooting light. Elevation adjustment is fixed at .438".