8" spread at 100 yards from a previously reasonably accurate rifle. The only time I had excessive spread, albeit, not that much, is when a scope went sideways. Easy enough to verify, try another scope after making sure all screws are secured. I seriously doubt it's a reloading issue giving your 8-moa spread at 100 yards. More likely something mechanical is very wrong either in the rifle or scope.
A 1,000 rounds out of a 223 Rem fired at a modest pace without overheating the barrel is not even close to wearing out the barrel. On the other hand, the "blasters" I encounter at the range, firing AR's burn through a couple of 20 round magazines in a few minutes until the barrel is fried. That's the only way I could see 1,000 rounds "burning" out a barrel. I have several 223 Rem precision bolt rifles that have 2,000 to 3,000 rounds fired through them and they still hold well under 1 moa, some in the 1/2 moa range. However, I do not fire sustained sequences.