5/16" drill bit? What size rivets did you use to fill the holes?
Or did you mean 5/32"?
The use of a drill bit smaller than a #30, and then rotating the drill will create holes that are not round. To do so will cause a water leak, gauranteed.
The Airstream "Service Manual" calls for a #30 drill bit.
The following drill bit sizes are the only correct sizes to use. To do so otherwise, is not recommended, by anyone that has had to chase down a water leak.
For a 1/8 inch rivet, use a #30 drill bit.
For a 5/32 inch rivet, use a #21 drill bit.
For a 3/16 inch rivet, use a #11 drill bit.
Using a chisel to shear off the rivet head, can result in scratching the metal.
Pushing the rivet shank out with a punch can result in deforming the metal.
Many methods can be used,"BUT" the safest way is drilling out the buck rivets with a #30 drill bit. Enlarging the holes with a #21 drill bit for the olympic rivet insures a round hole for proper fit.
Each aircraft mechanic may have a particular technique, that works for them, simply because they do this everyday, and hundreds of times, everyday. But, for the do it yourself person, using the tried "AND" proven way, is the best way for them to avoid trouble, and, insures a quality and permanent repair, the first time.