I have a new AR10 and when I pull out the takedown pin to pivot away the receivers, and then try to reconnect them, I can see the hammer impinges the back side edge of the firing pin, rather than stopping behind it. Of course this stops rejoining the receivers. The only way to reconnect them is to cock the hammer with my finger to stop it from bumping the firing pin, or to cock the hammer with the charging handle before separating the receivers.

The manual does state "The hammer must be in cocked position to join the receivers", but it doesn't state anything else - and I would expect more explicit instructions.  Is the hammer hitting the edge of the firing pin why they advise the above?  Does anyone know if either way of cocking the hammer before breakdown is acceptable?  I own a Colt M4 and the receivers rejoin with the hammer uncocked.

Thats how it is. 

 

Yeah I notice the back of the AR10's pin sticks out just a millimeter or so more than the colt's, and it rebounds when I push it in, which the colts doesn't do. That must be due to the spring in there you're referring to.....thanks for the tip!