I have a side by side Leige 10 gauge.The receiver is loose at the butt stock.I suspect more than just loose possibly a wood problem.
2nd view
With hand pressure the gap can be closed
Is the stock cracked beneath the tape or camo job ?
If so... take the stock off and see if you can reglue and clamp up
No not cracked under the dip.I found a smith that thinks he can tighten what he can and bed the stock and reciever