I can only echo Dustin, I can't understand how it can be a 'wristbreaker' but be 'assisted' in closing. A 'normal' wristbreaker is powered open by the main springs and as soon as one starts to close it one feels the, usually, heavy resistance of those same main springs. In fact if one isn't quite vigorously with one's closing effort, the gun bounces right open again. I wonder if your gun has an interesting variation of the 'normal' mechanism. It may be a lot rarer than you think!
I'll post a few pictures of the internals of Joe's gun that I took when restoring it for him sometime soon.