Look at things on the bright side. When you are done you will have two rifles ! An AR-10 and a LR-308 . But don't be too frustrated sometimes mistakes are the best way to learn. Ask questions , that's what we are here for .
Saw the TV clips last night . Ask GF is Rob is going to do a cameo role. She was laughing and said it would be in the indoor gun range and those two clowns would shoot him.
I blew out three buffers in my 9mm AR ,solved it with $1.00 in Canadian quarters. Buffer was bouncing and slamming into the back of the BC. Get another buffer and put some quarters at the back of the receiver extension.
Then load the spring and buffer .