RRA 9mm i changed the upper receiver to a A1 slickside from brownells it has a A2 rear aperture and a A2 frt post. Frt post is bottomed out and its shooting 6 inches low at 20 yards.Are there different height frt sight bases? any idea's Thanks MGP

was it a flat top before you made the change?  I think you gotta get the taller or maybe shorter post.  I think it will be a shorter post for the front sight.  

Quoted: was it a flat top before you made the change?  I think you gotta get the taller or maybe shorter post.  I think it will be a shorter post for the front sight.

It was a flatop.  i just filed down the post im gonna try that but the post is sticking up just a little bit and it looks funny but if it works its going to have to look funny. What posts are used in the colt 9mm? Thanks MGP

I think you need to find a A2 post,   the Flattop post are taller than the post on A2 uppers,   dont hold me to that but am positive.

Ok i filed down the frt site post a little bit shorter than the factory short post and it worked perfect the only problem was the post was barely visable so to correct this problem a took the frt sight base and milled .100 off  and now we have perfect sight picture

Dang, sounds identical to the problem I had with my RRA 9mm upper.  I sent mine back to RRA, and they wound up installing a new barrel.  Fixed the problem.  I'm using an ARMS 40 rear sight.

Mine is a flattop.  It appears that at some point in its life, the barrel was threaded for a flash hider.  Bad news was, it was threaded 1/2x28 (AR15 dimensions).  My thought is the crown got messed up, as it is very thin at the muzzle.  I could be wrong, though.

MGP, where/what did you mill?  The flat on top of the FSB (where it says "UP")?

Steve

''MGP, where/what did you mill? The flat on top of the FSB (where it says "UP")?''

Yes the up with the arrow is gone now but it works  Thanks MGP

Cool, Thanks.  I had thought about trying that with my [now] spare barrel ass'y.  I still might, 'cause you can never have too many AR parts lying around