Fig. 2 shows a part of the arbor upon which the receiver turns. _b_ is the portion thereof which is immediately below the chamber in contact with the barrel, and in this part a channel or groove is made descending from the point _b_ in both directions, so as to form two inclined planes meeting at the point _b_. These planes or sections of the grooves may form an angle at forty-five degrees with each other. This groove or channel serves as a chimney to conduct off the smoke of the lateral discharge, so that it shall pass directly between the receiver and the barrel and prevent its spreading, so as to pass in between the receiver and the arbor and the barrel and the arbor, and consequently from condensing there and rendering them foul. The barrel is connected with the receiver and with the stock of the gun by the aid of the arbor which at the rear end, is a solid piece with the shield or solid piece of metal which receives the recoil and constitutes a component part of the metallic frame-work or foundation of the lock and its appendages. The part C of the arbor is that upon which the receiver revolves, and the part C′ enters a cylindrical cavity in a mass of iron, D D, to which the barrel is brazed or otherwise attached. Fig. 3 shows the piece of iron D D and a part of the barrel B which is attached to it. The dotted lines in this represent the cylindrical cavity which receives the outer end of the arbor C′. The two are keyed together by the passing of a suitable key through a mortise in the piece D D and a corresponding one in the arbor. _c_, Figs. 1, 3, 4, and 5, represents the key. Fig. 4 shows its upper and Fig. 5 its under side, _d d_ are two fluted channels along its upper side to receive the heads of two screws which are screwed into the piece D D close to the mortise and on the side opposite to that shown in Fig. 3. The heads of these screws lap a little over the mortise and are received into the fluted channels _d d_. These heads prevent the key from falling out and check it in either direction, and must be withdrawn in order to remove the key. As the key _c_ is to act laterally as a wedge to draw the receiver and the barrel into proper contact, it is of importance that it should be checked when forced sufficiently far in, or the receiver might be wedged up and prevented from turning. For this purpose I insert a screw, _e_, Fig. 3, into the steel button _f_, which is attached to D D, to strengthen the end of the mortise and prevent the bruising of it by the recoil. The head of this screw, overlapping the end of the mortise, receives the wedge and checks it. By turning this screw the force of the wedge may be tempered. In Fig. 5, _g_ is a spring-latch on the under side of the key, which catches upon D when the key is forced in and prevents its accidental removal.