I received the stainless steel rivets for SB0014 and did some tests with them before shooting them into the main spar.
I drilled a 4.1 mm hole and an oversize hole of 4.9 mm.
The hole diameter is very important, if the hole is more than 4.3 the tail will not form nicely! When the hole has the correct size a nice large tail is formed of about 6.3 mm.
Note: these rivets have a thicker mandrel and need a 4,8 mm nose piece on the rivet gun!
The holes in the second flange are about 6.25 mm so if both holes are perfect aligned the tail of the rivet will form nicely.
I asked Mike from TAF and he said that this is no issue, TAF did tension and shear test with rivets formed likes this and they had sufficient strength.
Since the top skins of the right wing are not yet on, removing the rivets on the bottom skin is easy because all debris can be removed easily. I removed the rivets, scuffed the surface with Skotch Brite, and masked and cleaned the area.