NAS1241 & NAS1242 - "oops" Rivets Baby Brothers
Nobody seems to talk about these - Solid Rivet, Oversize Shank, per MilSpec, as listed in Genuine Aircraft Hardware, Inc catalog, Page 213 (Ref. Book 7).
These are rivets that have a standard size head (for the same "dash" number), but the shank is upsized by 1/64" (approx. .015"). As noted in the title block, they do come in both Universal Head & Countersunk Head shapes - which makes them suitable for repairing slightly oversized holes requiring a universal (domed) head.
Although a .015" diameter increase in size doesn't sound like much, in some cases it can make all the difference.
Example: You have a rivet location that is difficult to "buck", and because of the required "stick out" of the shank, you are having trouble keeping rivets from "clinching" over.
The standard pilot hole for a -3 rivet is a #40 drill bit - nominal diameter = .098", when you dimple that hole, with a similarly sized pilot on your dimple die, that hole diameter increases to somewhere between .104 - .105". With the -3 rivet diameter of .092" (typical - checked with micrometer), there is a significant "volume" that needs to be filled in the joint before any shop head can be formed. Ergo, the rivet shank needs to be quite a bit longer (microscopically) to both fill the annular void around it, as well as developing an acceptable shop head.
Since the enlarged, dimpled hole, is already (call it) .104" and the shank diameter of the NAS1241/1242 rivet is .107" (by msmt.) - by reaming out the hole (approx. .003") to .107-.108" to accommodate these rivets you get a "zero" clearance fit at the outset, and all of the rivets protruding length can be used for setting the shop head. In some cases, this will allow a shorter rivet (maybe only a 1/2 length reduction - but that may be enough).
Whenever I have these situations where clinching, or unacceptable shop head development is a possibility, I go the reaming route and shorter NAS 1241/1242 rivets.
Just my perspective - YMMV
HFS