I have 26" douglas barrel that has been on a diet of moly coated bullets for past 2 years.
My round count is 850.
Just in the last 100 or so rounds the throat has moved from a 2.296" oal to the lands to a 2.356" measured with a comparitor. I have been shooting normal loads for this caliber and my thoughts were to use the moly to see if I gained any more life out of the barrel.
I only cleaned the barrel when the groups started to spread. it has been a very consistent 1/2" moa to 2" groups at 300yrs.
I was hopeing to get over a 1000 rounds out of it but at 750 rounds it gave up.

By giving up just how bad is it? My 6MM Remington has close to 2000 rounds thru it's barrel, mostly hot loads using 100 grain bullets and it still shoots MOA or better. I don't let the barrel get too hot and clean it every 40 rounds or so.

I would suggest a thorough cleaning using Wipeout and then JB Bore Paste. Get it really clean. Seat your bullets out a little more than normal. Fire about five rounds of moly-coated bullets before firing for group. See if this doesn't bring that barrel back to life.

thanks for the comments, I did that and accuracy was about moa.
I have a reamer comming and plan on rechambering and setting the barrel back 1 thread or so should put me back in the game
Dave

HV, I shoot a Cooper .243 AI and haven't had anywhere near that much throat erosion. I am curious as to who's barrel is on your rifle, and is it button or cut rifled? Is it possible that the overall rifling is extremely shallow? Regardless, be sure to do a new crown at the same time as the setback. Good shooting.