Jim, the first 600 rounds put a lot of taper on the height of the lands, the second test is fubar in my opinion.
I shot out a lot of 243 AI's on dog towns years ago using Hart stainless with zero freebore, 12 twist.
I would put 1000 rounds on each barrel per trip and measure the throat wear. We shot these barrels as hot and hard as you could imagine, dumping out .050 rounds and shooting as fast as you could load and acquire targets.
Typical throat wear was about .070 in the first 1000 rounds and after 2000 rounds we would set the barrel back. On the second chamber, the throat wear was usually about 0.100 or a tad less on a 1000 rounds.
We shot Win 760 exclusively with 70g bullets.
Stick powders ate barrels, especially 4064.
Jim, in your test, chrome moly was used on your barrel and it may indicate just how much faster chrome moly may wear and the powder you used was a factor also along with the bullet weight.
I thought ball powder was harder on barrels than stick powder?
