Here's a start:
http://www.hootalrifleshop.org/over_the_log_shoot1.htmA little more:
http://muzzleloadermag.infopop.cc/eve/forums/a/tpc/f/20610091/m/9361099152/p/1NMLRA:
CHUNK GUN
5400–NUMBER OF SHOTS–The target is a white X on a black background with three shots fired for score. More than the required number of hits
will be the same as Rule #10590
5410–CHUNK GUN RELAYS–The relays for this match will be 45 minutes in length, or as stated in the program.
5420–SIGHTS will be open fixed, as per rules #5010 and #5020
5430–CHUNK GUN RIFLE The rifle may be either flint or percussion ignition, of either the traditional hunting or traditional target type, or as
specified in the program, with no limit as to weight or caliber. The rifle may not be equipped with a false muzzle.
5440–SHOOTING POSITION–The match will be shot in the prone position with the muzzle of the rifle rested over the chunk. Kneeling or sitting
behind the chunk is not allowed.
5450–TARGET SCORING–The match will be scored by string measure. From the center of the X to the center of each shot hole, shortest total string
measure wins.
5460–CHUNK DESCRIPTION–The chunk may be any round, square, or rectangular block of wood that is of a size suitable to use. Small blocks of
wood, padding , or sandbags may be used on top of the wood block to raise the muzzle.
5470–PAPER SPOTTERS–Will be made by the shooter and may be of any size, shape, or color. The spotters may be pinned, stapled, or taped to the
target the way the competitor wishes.
5480–GROUND COVER–The use of shooter-supplied ground covers to lie on is permitted.
5490–TARGET DISTANCE–The targets will be hung at a distance of 60 yards in front of the firing line.
5500–WIND FLAGS–Are allowed in chunk matches, as per Rule #2340
5510–SPOTTING SCOPES are allowed in chunk matches.
5520–COACHING–of a competitor is not allowed in chunk matches, in accordance with rule #5000