although 1500 rounds is a rather small total, remember barrels are like tires.... they can/ do wear out and must be changed

additionally one of my AI factory barrels required a good scrub around the 1K mark.... it took damn near 60 rounds to get it shooting again.... ~30 to get 1" and another 20-25 to get it back down to 1/2"........ just keep that in the back of your mind

Also, if you are sizing your brass different and changing things up by how you load them, that can change up the load. The name of the game for accuracy is consistency. Do the same thing each and every time from round to round the same. When you change things, the load changes, and the accuracy can easily change also. I know my 260 Rem took about 150-175 rounds before accuracy fell off. My 300 WM was about 60-75 rounds. My 6.5x47 Lapua is about 100 rounds, but it's still a new barrel and I'm still learning the personality of this barrel. But if you are running a VLD, seat it touching the lands, but not jamming. You should have plenty of room in the mag with a CM. Also, if you change lots of powder, recheck the load. I've seen as much as 120 fps change from lot to lot with H4350 and Varget.

My 6.5 Creedmoor, with a 140 A-max, and H-4350 was a charge of 42.4 gr. Once I went to a new 8 pound keg, the new charge became 42.8 gr, achieving the same velocity, and the same consistency. The way I found the new charge was just built a 5 shot group below, at, and above the old charge. So I went down to 42.0 and 42.2, old charge of 42.4, added 42.6, and 42.8. Found the new charge and reproduce it as needed.

You never answered about removing the rifle from the stock. I've had that make a definite change for the worse on a rifle. For that matter, did you say whether the drop-off was from one range session to the next or was it gradual?

And how crappy is crappy?

yep, I did answer and no I haven't messed with the stock.

crappy as in 3 rds in 1 1/4-1 1/2

Clean the bore down to bare metal then foul it again and see how it shoots. If seating the bullet out a little further ("I've reworked my loads") didn't work, it's likely you need to removal the metal fouling and start over.

And did the change happen between two sessions, or gradually?

When folks are saying to clean the bore, they are suggesting that you clean it with something good enough to get the copper out. Not just anything will do that. I use Boretech Eliminator.

And, if the cleaning doesn't get you the accuracy back, swap out the scope. I've had two scopes give it up in the last two years. In both cases, accuracy loosened up to about what you are seeing. When a serious cleaning didn't fix the problem, I decided to swap the scope out for an old trusted one. And...it was the scope that had gone bad. Both bad scopes were on the same rifle, which is my 223. Not exactly an elephant gun, so suspecting the scope was the problem just didn't seem likely. Oh well...

Have you measured the throat?

Like others have suggested. remove the copper to bare metal then foul and try again. Even those that suggest never clean the barrel will at some point usually well before 1500 rounds.

I hope I'm not lumoed into that group. My M.O. is clean them when they tell you they need to be. It seems as this rifle is screaming that it wants to be cleaned if we can eliminate all other variables. I think we have. Some barrels need it very early, some run for hundreds of rounds, shooting tiny, before they need it.

I'm pretty much in Fireman's camp on cleaning, and I know about when most of them will need cleaning. It's almost always accuracy related. I have noticed that the after market barrels, except for the Sako, need less frequent cleaning. And that Brux barrel that Chad had put on my 260 is special, in that I shoot it and shoot it and the accuracy never seems to fall off. I guess I'll just clean it every season.

I cleaned it BIG TIME and then noticed when I dry fired it there was movement. I checked and found that the Scope base was just a little loose. I took it out and shot it this afternoon and it was back on. I did notice that after the first group it started stringing a little, vertical. Can you tell me what causes this?

Thanks,

How many rounds total did you fire?

A loose scope caused me to string vertically. But I'm guessing since you just tightened up the bases then you checked the rings too

Yes...Actually I took a tool to everything to ensure things were completely tight.

15, first 5 was used to site in an then to confirm Zero. Then I fired two 5 shot groups and had vertical stringing in both. one group all five were touching, the second group 4 were touching with the fifth was simply a poor shot on my part.

Keep shooting it.