I'm assembling my lower receiver and having a problem. It's an RRA parts kit and a PWA stripped lower receiver. I was following the assembly instructions on this site and got to the hammer installation. If I put the hammer in with a punch serving as the pin, it seems to function properly. But when I put the pin through, it doesn't work. The hammer is really stiff and doesn't want to move much. I checked the pin, it looks fine, and it will fit through the hole in the hammer and both of the holes in the receiver. I can put the pin in the hammer, the J-pin catches and it seems relatively smooth. But when it's all put together, it doesn't work. Any ideas? Am I missing something obvious?

This morning I was at it again. I took out the trigger and took the spring off of the hammer. When I put it in like that, all by itself, it does the same thing, even some with the punch. I can't see that it's hitting anywhere, so it seems to be there's something wrong with the fit between the hammer and receiver at the studs on the hammer. Anyone else ever have that problem? Should I try to take a little off of the hammer studs? Are the studs on the hammer supposed to be slightly crooked? Because they not only look crooked, but the marks inside the receiver from trying to move the hammer indicate that too.

Thanks in advance.

This just doesn't make sense?  You say that the hammer works just fine when you use the punch as a pin to hold it in place BUT when you replace it with the bin it seems to bind or jam...

That would indicate to me that your hammer should be fine?  Are you sure you are putting the spring in correctly?  

I need to have a lower in my hand to try to understand so perhaps I can give you more feedback tonight?  RRA maks very good parts kits so I would be quite surprised if there is something wrong with your hammer, but anything is possible?  

Perhaps I can disassemble my Bushmaster tonight and show you how to do it...?

Quarterbore, I should have posted a link, I got the problem solved.

http://www.ar15.com/forums/topic.html?b=3&f=12&t=159732

The tubes on the hammer were just minutely too long. As for the punch, it's because the hammer didn't want to go into the receiver far enough to line up with the holes. But when I was using a punch, the punch I was using at the time was much smaller than the pin, so it didn't have to line up that much. When I would use a bigger punch, it was the same way as when I would use the pin.

Good to hear you got it fixed and thanks for sharing the solution!