Eswanson- Yeah, that's a problem..
One of two things could be occuring. I'll work on the assumption that this rifle has no disconnector..
First, when you take it down,
(Large thumsrew, right hand of the reciever, above the trigger..The action should split, leaving the left side of the reciever, and the rear portion, while the right upper reciever, and barrel assemblies come loose.. )
you should be able to see the sear surfaces. Note any wear, or fouling from lube..Trying the action, to see if the hammer falls on a spent case would help the diagnosis..
Second, inspect the bolt, and see if the firing pin is frozen in place. Not a common problem, but I've seen at least one AR-7 turn into a full auto from this..
I have some B&W piccies of the rifle, but they are very detoriated.. Any you post can help..
I'll see if I can find more info..
Meplat-