I recently purchased a Polymer80 kit with everything needed to build their version of the Glock 19.
At first the gun was very very tight to the point that it was very hard to even cycle the gun. Come to find out the lower parts kit had an extra pin in it that was made out of plastic.
When I assembled it I didn't notice that it was plastic and disregarded the apparently steel pin that holds the front rail in.
After I installed the steel pin things were much much smoother, but still pretty tight. I knocked off the rough edges of the front rails with a file, and ran some polishing compound over the front and back rails for good measure. It's so smooth now that it almost feels like it's on ball bearings.
I went out and shot it yesterday before the polishing, and today. Post polishing the gun ran like a top. I started out with a normal two hand grip, then one handed, and finally just holding on with trigger finger and thumb. The gun cycled just fine even with just a two finger grip, and the slide locked back on every mag.
I will be taking it to and IDPA match tomorrow to let other people shoot it and put it through its paces.
I purchased the complete kit for $450 shipped from www.80pbuilder.com.