I am going to build an AR47 and was told that some flattop uppers are different widths as per manufacturer. Any want to throw a caliper accros the outside of your uppers in the area that the magazine would run up inside?

Thanks.

The outside width dimension you are asking for isn't going to help you much since the machined features of the all uppers do not reference from the outer dimensions of the forging in the magwell area.  The right side web is going to be thinner than the left due to the cut for the dust cover.

Per ARDEC Drawing 9349063 for an A2 upper, the width of the [b]inside[/b] of the magwell opening at the lower edge of the upper receiver is 0.925 +/- 0.010.  This is probably going to be your critical dimension.  I know of no reason this dimension would be different for an A3 (flat top) upper.

If you are looking for a flat top upper with lots of excess material thickness in the magwell area that can be opened-up, then you might want to consider the DPMS High or Low- Rise uppers.  They are a rather thick-walled aluminum extrusion with no dust cover or associated cuts.

Material has to be removed form the inside of the upper to accomadate a wider AK mag. The guy that makes the lowers tells me that some makes of receivers run a little wider on the OUTSIDE in this area. Therfore after removing the material on the inside of the upper the walls are left a little thicker. He said most Colts are a little thicker.

Yup, the low pro would be the way to go, but it's kinda ugly (IMO) and it is a little higher so I assume a carry handle or added sight wouldn't work correctly.