1. Narrow your trunnions. Because the extra thickness of the shell is on
the inside (if it were on the outside, the axis pins would not be long
enough)you will have to narrow your front and rear trunnion by .6mm on each
side.It is important that you do it evenly on each side so the barrel and the
rear tang stay in the middle of the receiver. We do it on a surface
grinder.
A handy person can figure out how to do this with much simpler tools.
2. Deal with the narrow groove on the trunnions. The top rail of the
receiver slides into grooves machined into the side of the trunnions,front
and rear. This groove is too small for the thicker top rail on our
receiver.
The first thought would be to widen the groove. Two things make this not a
good idea. First, the trunnions are very hard, and difficult to machine.
Second, you would have to made the cut symmetrical to the groove-it is
important that the barrel trunnion be at the right height in the
receiver relative to the bolt rails, so if you cut the extra metal at the top of
the existing groove, the trunnion would drop down in the shell, and the bolt
will drag in the bolt rails.
The right way to fix this is to narrow the top rail from the bottom
only. You can carefully file or dremmel the bottom of the top rail until the
trunnion will slide onto it. Note that if you removed the material from
the top of the rail, you will be lowering the trunnions again, with the same
bad effect on the bolt fit into the bolt rails. This is really not a
difficult thing to do. We considered doing it to all of the shells we sell without
trunnions installed, but we decided it was not a good idea.
3 Selector lever. Selector levers from a milled receiver will work fine
without modification. The wall thickness on our shell is identical to
the milled receiver. With selector levers from a 1mm sheetmetal shell, you
will have to open up the gap between the inside and the outside parts of the
selector just a bit. We are including a piece of the metal we make the
shell from as a gauge, so this will be very easy to do.
Global posted these instructions. You should have got a sheet with this information when you got the receiver. I got a sheet for each receiver I ordered. I used a mill to narrow the trunnions and that worked out well. Measure your trunnions they gave a ideal measurement but I don't have it at home, I will post dimensions tomorrow.
I found the dimensions:
The design dimension is 30.8mm, with a tolerance of .1mm plus or minus. So in SAE, a finished size of 1.213" ideal, no narrower than 1.209", no greater than 1.217".
You should measure your trunnions before removing any metal. I think there is a slight differance in manufactures to warrent checking.