For nothing but a target/tactical style rifle, what caliber would you go for for up to 1200yds.
Why are you limiting yourself to 1200 yards? Is there a local competition that goes that far? Is that all you think you want to shoot? Or is that the limit of what you have nearby?
Frankly, if it's anything other than the last one, you will want to go past 1200 yards the minute after you make your first 1200-yard hit.
Non competition. Strictly making hits on steel. Without going overkill like a 338.
The reason I ask the questions above is because many things are overkill if 1200 is all you're ever going to do, including the bigger 30s.
Target rifle. Seems like 6.5creed is a great choice, but it gets a lot of hate here for some reason.
6.5CM gets its hate because so many shoot it and many that do espouse it to be the best round ever. It's a solid all-around cartridge that has gobs of factory ammo available (likely - and I only say "likely" - second only to the 308 for what you're looking for). If I were to get a rifle in the 6.5 CM class, it would be something that gets a little more speed - perhaps a 260, or even a 260 AI. But to do so, you really need to reload.
Frankly, with the information you've given, there are too many variables to give you a solid answer.
- Are you recoil sensitive?
- Are you price sensitive? (ammo/component cost)
- Do you reload, or are you going to get into it?
- Will you ever shoot 1500, mile, mile+?
- Where you shoot, can you easily spot misses (e.g. dry dirt), or is it grassy or wet dirt?
The list goes on and on.