Seems like there is a rule of thumb regarding groups. All factors
being consistent in case prep, loads, OAL, etc., is there a rule
of thumb to use for tightening up groups?

If memory serves correctly, one can try OAL adjustments or powder
adjustments if a clover-leaf group is a bit large. And an
adjustment if there is an occasional flier in an otherwise tight
group.

Is there actually this "Rule of Thumb", or have I just been
dreaming?

If you have worked up the best powder charge for your particular rifle then I would start changing the seating depth. Remember, only change one factor at a time. I always start at a full jam and work the bullet in from there. I usually go .005 increments. Use a couple of wind flags so you know if it is the load or wind. Be honest with yourself about poor shots (shooters error). Sometimes a nice clover leaf is the best a particular rifle will do.

Good luck,Matt.

DB, do a search here for 'Creighton Audette Load Development Method'

I think one of our very knowledgeable posters here says it is properly stated as 'The never improved upon Creighton Audette Load Development Method'

I probably mis-spelled the title or some part of it, and will probably get scolded for it, but hey, in the sake of trying to steer you in the right direction, it is a method which with minimal components gets you to the most accurate load for your gun.

I use a simplified--or as those who know me might say (a dumbed down) version of the Audette Ladder--

Good Luck!

I have found over the years that each rifle is just diff. Some will respond to OAL adjustments, some primer changes, you just never know.

my first rule of thumb is to try not to hit it with my hammer..................

LIFE IS SHORT.....

Screws tight-Barrel clean and fouled with at least two shots-Federal Primer-Powder reccomended by most manuals. This is my list, when they don't work look at the rifle very, very carefully, not to forget mounts for the scope, etc. Good shooting.

If your going to buy something, dont go cheap. You end up spending more in replacing it.
Which is very true with most things gun related and extremely true for hell, ... I mean walmart.

If your not sure if you cant take the shot, dont take it. Be damn sure your going to get the kill in one shot, dont spray and pray, there is no sport in that.