The hard stop is normal. It means you have bottomed out the threads and the screw can go no tighter. If you're still using the plastic pivot washers they have worn or compressed to the end of their useful life. Replace them.Many on GTA opt to replace them with bronze or brass washers instead. I have attached instructions for fabricating these washers as well as adjustment instructions.
If it's that new Crosman would probably send you some washers at no charge if you asked. The bronze washers are a better option in my opinion but it's your choice.
I know this is old hopefully someone is kind enough to respond. Me and my father just started air rifle small game hunting so I’m pretty new. So I think my issue is the lockup as well. I set a target 15yds away and I can’t hit a 12x6 piece of paper and it sounds like the pellet is falling short of that makes sense? I did the trigger mod and the front screws don’t have either washer (rookie mistake) as they must have fell out. Can I go to Home Depot and get a replacement set... and if so what size would I be looking for? Thank you in advance for any suggestions.