Brother, that's gonna be a torque issue, over a thread-locker issue, no doubt.
Here's the deal with purple - it's all about the screw size. Those handgun optics screws are so tiny, that Blue Loc_Tite will actually seize those things in place, and you'll strip the heads when you try to remove them to change a battery, or something like that. Blue is just too much, based on the screw size.
Here's a cheater chart:
I use Green, too, when it's serious. I don't use that 290 stuff in the picture above, I use 670. My definition: Bearing retaining compound, serious shiit when I don't want a wheel bearing outer race to move. If I need to change wheel bearings, I have to do it with a 20 ton press, or blow through a whole bottle of MAPP Gas to heat that shiit up and make it easier. I'll use Green for motorcycle footpeg bolts, too - I don't ever want those fuqrs falling off...
Purple has it's place, and those tiny ass screws are the perfect place.
I'm a big fan of Vibra-Tite, as well. For gun shiit, I think it's the better product. For suppressor-host muzzle devices, there is only one... Rocksett.
My $0.02...