[bluesea112]

Goofy is right. Slight changes between manufacturers can create headaches for you. Just 1/1000 of a difference between manufacturers can cause something not to fit exactly right.
I personally own a Heavy Barrel DPMS Panther LR308. I have never fired at a 300 meter target, but I can tell you that at 200 meters it punches a 3" group all day long with store bought ammo. I can squeeze that down to 2 1/2" at 200 meters with my hand loads. Best of all, it fires anything I feed it without a hiccup. It doesn't matter if it is Remington, Wolf, Silver Bear, Federal....it cycles it all and never jams or misfeeds.

The best thing about buying a rifle from a single manufacturer is the warranty. You will spend $1200 whether you put it together yourself or buy it already assembled. If you buy it already put together, you have a guarentee that it will work. If it doesn't, then all you have to do is send it back and let them fix it. If your project rifle doesn't work, you could spend lots of time and money trying to figure out what is wrong.