I had this same issue and couldn’t find a resolution online. I purchased a factory new Benelli M1014 “special edition” with the fixed skeletonized stock. I could not get it to lock in a vertical position. I contacted Benelli customer service and got these instructions;
INSTALLATION/REMOVAL OF 1 POSITION M1014 STOCK
1. While depressing the button on the stock, slide stock on tube in the 10 o’clock position.
2. Slide the stock all the way forward.
3. Rotate stock to the 2 o’clock position.
4. Pull the stock all the way rearward.
5. Rotate stock to the 12 o’clock position.
This worked for me. Hope it helps someone else.
