There's nothing new going on here, but Kalix have changed the expectation. At an unbelievable price, I still can't believe I bought one. But......
Kalix have a solution.
Plenty of brands make a mechanism, but it not only involves a big curved cut in your stock, which is tricky to do with home tools, it also needs lots of patching and filling. Before you get to the bit where you need to make the two sections line up.
Kalix. Stick template to stock, drill four holes. Ya done.
Kalix also make a rather elegant solution for wooden and solid stocks. More about that another time.
Your pal
SBW