A convertible gas piston conversion system for the AR-15, AR-10, or their variant rifle platforms is provided to convert the platform from a direct impingement gas system to a piston driven operating system. The conversion system includes a gas block having a barrel bore and two piston cylinder bores one on either side of the gas block. One of the piston cylinder bores is for utilization of the AR-15 rifle and the other of the piston cylinder bores is for utilization of the AR-10 rifle, making this piston system convertible for either the AR-15, AR-10, or any of their variant rifle platforms. A piston cylinder is inserted into the gas block via the piston cylinder bore and a piston is actuated inside the piston cylinder to cycle the rifle. A connecting link is coupled between the piston and an op-rod making the gas systems length adjustable by simply replacing the connecting link. The op-rod acts directly upon a carrier lug to cycle the rifle and a compression spring or the like returns the piston back into the battery within the piston cylinder. An op-rod bushing guides the op-rod throughout travel. A bolt carrier includes a lug and an anti tilt/anti wear device. The bolt carrier provides a lug for the op-rod to impinge upon to cycle the rifle. The anti tilt/anti wear bolt carrier device installs into the rear of the bolt carrier to minimize damage and wear to the buffer tube and upper receiver from a condition identified as carrier tilt.