Tim,
Thanks for the tips. Actually, I had tried to pancake it between 3/8" dowels the first time, but I don't think I got good expansion of the slug. What I did this time was to take a hammer and anvil and preshape my slug (egg sinker) to slightly over bore diameter (about .440"), and then grease it and lightly tap it into the muzzle with a wooden mallet, so that it engraved the lands and grooves on the way in. (I was kind of afraid to do this, but then remembered that my muzzleloading conicals always engrave as I short start them, so muzzle steel should be able to handle it.) After getting it into the barrel, I pancaked it to make sure, and then pushed it back out. It made a good casting of the lands and grooves.
So, to UPDATE THE MEASUREMENTS I gave previously, the correct groove diameter on my new 44mag handi barrel is about .429" (average of .429", .429", and .428"), and the land diameter is .423". Again, rate of twist is 1 in 38". (Sorry I gave bad data earlier.)
FWIW, I checked the calibration of my vernier caliper by measuring some automotive feeler gauges, and it appears to be properly calibrated.
Still, I wish this gun would shoot Hornady XTPs as accurately as my muzzleloader does. I haven't yet figured out why its not shooting well.
Duane