After the datum holes I drilled the corner holes for the mag well with a long 7/32" drill bit then moved inward and plunged an extra long 3/8" carbide 2-flute endmill in to blend points in the corners.
Then used a long .75" 3 flute endmill to take out the material in the middle of the mag well.
Then I changed the setup to mount the receiver over parallels on my rotary table that has a 16" diameter sub plate mounted on it. so I could use the same 3/4" endmill to rough the side wall angles in. I believe this mag had 12d 18' angled sides.
Then finished them off with a long 3/8" 4 flute endmill.
Neither endmill would quite reach all the way through the block, I expected to have to flip the part on the rotary table to finish the cuts all the way through but was able to use a hand file to finish them off.
While I had the part clamped to the rotary table I went ahead and cut the FCG pocket since there are two angles in it that would require the rotab anyway. Since this was done over several days I made sure to recheck my zero location at the start of each day and anytime the rotary table was moved.
Here you can see the two angles where the receiver starts tapering down to the safety on the receiver.
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