Originally Posted by tmitch
The problem with the Mark II and the Buehler/Timney is that they rotate the wrong direction in order to place them on the right side of the bolt. I've installed a couple Mark IIs on Mausers and and still have one on my Siamese .45-70. A good bump on the bolt and all of them would lift and move off safe. Not sure who the makers are, but the ones that fit on the left side of the bolt will not rotate off safe if the bolt is lifted because the bolt rotation forces it towards the "on" position not "off" like the one that fit on the right side. There's a nice case hardened one for a Springfield on eBay

Yep, it appears it's hit or miss, and just a few thousandths separates a right hand side Buehler or Mark II from one that locks the bolt always, to one that will pop off with a hard hit on the bolt, to one that will pop off with normal bolt lift.

Cheers,
Rex