Usually for me just thread alignment or debris, some are just made to tight?some work fine on some and same one will clip on another gun? I usually buy a caliber big or open them up .020” if they clip, not a big deal. My best success is with a 25 cal for 22 cal, works great, they don’t need to be slip fit to work great, the worst ones are the one that barely clip sometimes, not all the time? Will drive you crazy. Hope that helps.