If you get a well worn one some of them could wiggle a bit. I have two new ones and they have a little nub that I had to file a bit to allow them to lock open and they are solid. The nub is there for that purpose, if you got a worn one you could hit it with a wire feed welder and build it back up then file it to your liking.
All the ones I have seen are real solid my only complaint is that they need a bit of a cheek piece but I have seen much worse.