Re: Ok so I have to ask....
My Son-in-Law's buddy just had three 770 misfires in a row yesterday, cost him a Doe. The primers showed extremely light hits. The fourth round actually fired; but the doe was already at full throttle.
I advised him to soak the bolt in kero overnight, dryfire it plenty, then flush it out with brake cleaner. Gun was bought used, performed perfectly at sight-in a few weeks ago. No real idea about what caused it or whether the above regimen is a solution, but as an immediate action response, it's probably a good start. If no joy, a bolt disassembly would be next, to determine the problem with incosistent firing pin protrusion.
The 770 is probably the very last action I'd choose as a build-donor. If you want cheap and good, try the Stevens 200.
Greg