Bailey I am looking at my AR as I type this and there is nothing behind the hammer, no through pin or bind pin as your pic shows. There is nothing in the space between the hammer and the break down pin. It appears there was never a block as there is no holes in the receiver to accept a through pin or a bind pin. I know pics help a lot but I can't get this older computer to co-operate. If I can I will send a pic. Is this gun legal?. I guess this was made before 89. Bailey thanks for the help