You will find in this page the main facts back in the building log on many subjects on which I asked .
For beginners like me : hold the pneumatic squeezer well perpendicular to the longeron, rivets will be even more rights.
The principle is : having to remove the least amount of rivets ! Each of these operations can dammage the hole of the part … so better to take 3 minutes to rivet rather than waiting three weeks the damaged part …
The round-headed rivet may be put on the two sides of the workpiece .
I started to put those rivets heads toward the reinforcement bar and thus crush the rivet on the side of the thinnest part.
Having asked Manu (Happy builder of a RV- 7) , he told me that the rivet heads always put the most fragile side for obvious reasons of strength.
So I left the rivets in place on the first length ( the “bad” side) and put the rivets on the right side on the second length . No importance , but it is a question of aviation construction standards.
A principle to remember for the rest of the construction.
Rivet gun 3x pressure used