Anyone ever had a problem where the retaining pin was too loose?

Just replaced my Colt 20" A2 Upper with a Colt 6721 16" upper.  The fit between the two appears to be perfect, but the rear takedown pin is so loose that if I tilt the weapon, it will fall out.  There was no problem before I changed the upper.

Thanks.

A2 STOCK

PARTS: takedown pin, takedown pin spring, takedown pin detent, stock, buffer extension, retainer, retainer spring, buffer, buffer spring
TOOLS: #10 (or larger) flat-blade screwdriver
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·Insert retainer spring and retainer into recess in lower.

·Install buffer extension, (buffer tube); press detent when necessary; torque to 35-39 ft-lbs add spacer onto stock tube, and insert stock.

·Install takedown pin with groove to the rear and install detent and spring from the rear of the receiver.

·Carefully compress the spring with the stock and secure the stock in place with the self-locking screw.

·Insert stock screw from rear into stock.

·With hammer down, insert buffer spring and buffer into buffer tube until retainer snaps up to lock it in place.

·Function check on takedown pin and buffer retainer.




My guess is that the take down retainer (detent) spring or retainer (detent) is missing from the lower (two parts behind the rear take down pin in the photo) .  These parts are retained in the lower by receiver side  face of the butt stock, and can be lost during a stock change if you forget to retain them during the removal.