Ale-8 knows this stuff.
The Long Rifle bore (diameter between the lands) is .217" and .219" for the magnum barrels.
An unused 7/32" (.219") drill bit will go in the Magnum bore but not the LR bore.
And check your drill bit with a dial caliper or a micrometer. Recognize the shank of the drill bit is smaller than the actual cutting edges, so use the cutting end of a new drill.
Another caveat is cheap drills can vary a couple of thousands especially on the shank, and if they've been tightened in chucks a couple of times, have been slightly deformed.
The .22 LR only gun's groove diameter is .222", these were only used pre ~serial #150,000. All Ruger .22 convertible barrels and LR only guns since then have a .224" groove diameter.
Note: "Bore" size has become a generic term; actual bore diameters are the distance between the lands, not the grooves. Typical actual .22 bore diameter averages .218". Hence the .218 BEE name to differentiate it from myriad other .22 cartridges.
The Single Six LR only .222" groove diameter ended at ~ #150,000 in 1959.
All Lightweight Single Sixes have .222" grooves thru #212,530 when they ended production in 1959. The S (seconds) model Lightweights assembled in 8/64 and 4/65 are all numbered below #212,530 and may have either bore because they were assembled later, some possibly with later barrels.
Bearcats were introduced in 1958 so those produced before 1960 likely have LR only bores; #s A001 thru X453, and possibly later. I don't have one that early to confirm.
Super Bearcats introduced 1970 (all steel except trigger guard until 1973) all have the .224" groove diameter.
