Ridin' the rails

Another one of the things that sets the PSG-1 apart from a standard HK G3 is it's reinforced receiver.  The sheetmetal stampings are basically the same except that the PSG-1 is missing the G3's scope mount lugs.  The PSG-1 receiver gets it's extra strength from some reinforcement rails that get welded to the side of the receiver.  As with most things, reproductions are available, but they are expensive and I am cheap, so I made my own.

This whole CETME projects is an exercise in fake it 'till you make it, and still there are times when I annoy myself because even when I'm half-assing things I often have to take the steps to do it "right."  I drew up some reinforcement rails based on pictures and the few measurements I could find online.  If you've been following my posts long enough, you know that I hate everything about machining steel and avoid it as much as I can.  I thought about 3D printing the rails and gluing them on, but decided that was too fake even for me.  Then I thought about making them from aluminum and bonding them on with JB Weld(which I'm fairly certain would actually work pretty good), but it still wouldn't be right with no visible welds.  So I finally settled on making them from steel...sigh...

I used plain mild steel and here's how the rails look after machining:

They look fairly straight forward, and they are, but the back side isn't really something that could be easily done without a CNC. The contour on the back side has to match the shape of the receiver.  Here's how they sit on the receiver:

 I was able to talk myself into some Tig time to weld them on. The actual PSG-1 has a single plug weld towards the front of the rails, and it wasn't until I stared fitting mine that I figured out why.  With a plug weld in that location, the rails, receiver, and trunion can all be welded together as a unit.  Fortunately I realized it before welding, so I pre-drilled the hole for a plug weld for when I weld the trunion in.  I also had to notch the right rail around the ejection port, which seemed wrong to me, but that's how HK does it too.  It's just five short welds across the top and bottom but I am very out of practice making small welds on steel, so they aren't the prettiest.  Low amps, no backer, no burn through, and I still have perfect bolt drop so I know I didn't warp anything.