Nice to see the ammo is doing good in your rifle.
I know you don't have a lot of that ammo available, and it's expensive, but I have noticed that with most bullets I load, especially monolithic coppers, that it will usually take 3-5rds to settle in. So only firing 3 and then cleaning probably isn't helping. I know when I'm getting my rifle ready for hunting, I will clean it real good, then take it to the range, fire 5 rds, let it cool down a bit, then fire another shot to check zero. After that, I don't clean it until after hunting season, and I'm ready to go to the range and fire something else through it.