When I assembled my lower I noticed that the hammer pin is walking. I reread the instructions here and it says that the J-pin should retain the hammer pin, when I look inside the hammer theres a hole but nothing there. Should this have been istalled when I got the lower kit or did I miss it in the parts. I checked the parts very carefully when I opened the package so my guess is that hammer pin retainer was missing. Help me clairfy this.

J pin should already be installed, it's an assembly that includes the hammer. Which L is this? BSW

The lower is 80% home built and I got the parts kit form sarco. I just got off the phone with them and they were very helpfull. The replacement hammer is on the way.

I got a hammer without a J-pin once.  I made a J-pin out of an old hammer spring leg.  You insert it into the hammer and measure for proper length, snip the leg off, insert it into the hammer, flatten the part of the leg you see in the "window" of the hammer and bend the lower part of the leg over the bottom of the hammer.  Just like factory.