Have you had the stock off of the weapon? If you have that is probably when you lost it. Due to if you over pull the take down pin to the point of the take down pin detente coming out of the receiver you would have damaged the receiver where the head of the take down pin setts down in the recess on the receiver. You will as you probably know, have to back off your stock or End Plate Adapter and Castle Nut slightly to reassemble the Take Down Pin the the Detente followed lastly by the Detente Spring. Is the spring damaged also. It is also a good idea to apply a little pressure to the rear of the spring when inserted and work the Take Down Pin to assure the Detente is in the Track on the Pin and works well. The Take Down Pin Detente as well as the Pivot Pin Detente dimensions are as follows. They have a slight taper to a point on the end that rides in the track on the Take Down Pin. Most have a slight point on both ends as you buy them so it does not make any difference to how you install them. If tapered only on one end the point must go to the track and the flat to the spring. If you have a problem with making or finding a pin PM me! Additional: You do not need quite as much taper as the samples below. Best I could do as far as shape on my computer.
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