Why was town marshal in the old west able to force  rowdy cowboys coming in town to turn in their guns? What about their 2nd Amt rights?

The "American Frontier" period is generally considered to be from 1607 to 1920 and a lot of the places that constituted the "wild west" didn't become states until late in the 18th or early in the 19th centuries. So in a lot of the places you're thinking of they may not have had Second Amendment protections because they weren't yet part of the US. 

You could also kill a man, and walk right away as long as he started the confrontation. Left's get back to that too. Whaddya say? 

For the most part they were territories not states so the Constitution didn’t apply

I think child control would work pretty good too. Some of the idiots I see having kids who are idiots. That is pretty scary.

People in the old west learned that people walking around town with guns was a bad idea. But what did they know huh now everyone has a gun and look how that turned out