[Kos-Mos]

You haven't been here long enough.
Most allow 500 with the certification.
I played at 575 a while back, but had to use a sidearm for anything under 100'.

There is no reason why you would need to upgrade your BAR anywhere that high.

If you really want an accurate gun, start with a decent 6.01 tightbore and use only high quality BBs (Bastards are really good in .36).
Also change the hop-up unit for a PDI while you are at it.
Then change the stock cylinder and piston to a PDI vaccum or LayLax 3-pieces.
Then get a zero trigger to let you have a more precise break-off, resulting in more consistent shooting.
Then replace the stock with something adjustable, like the PRS from Magpull. It takes some work to fit, it is not a direct bolt-on.
Then you will have to get a good quality scope. Don't buy a chineses replica, buy a real hunting scope. About the same price, but the hunting scope is more accurate and usually a lot clearer.

Then, and only then, buy a 9mm spring guide with bearing and a stronger spring to bring your rifle to 430fps (if not already there).

Theses are spherical BBs, not bullets. They don't shoot further the harder they leave the barrel. Take a ball of paper, what ever how hard you throw it, it won't go much further. Throw is slow and steady and you might be able to hit the same spot over and over. You have 1 chance with a BAR. The enemy has about 20 per second. The "range" you have over him can be covered in maximum 2 seconds, so you better not miss that first shot.