My old ass KSC USP compact (pre-system 7) was a sniper rifle at 160ft. Had something ridiculous like a 2" grouping, and it was all stock.
Pistols with good hop rubbers can be VERY accurate, what's NOT accurate is you lol
Anyway, the 300ft range for a pistol is more about muzzle energy than anything else.
A tightbore will get you another 10-15fps, but ultimately you really need another 80.
This is the only time I'll say it, but you'll actually need a longer barrel.
It won't affect accuracy for better or worse, but you need the extra barrel length just to accelerate that BB more.
Something like a 160mm 6.01, using .32s, and either a good damn soft hop rubber or an Rhop.
But either way, 300ft shots with a pistol (If the pistol is even capable of that range) is pretty damn hard to do even when it's braced. It's hard enough to do with a full length rifle, prone, with a bipod.
200ft is far enough, I don't know under what circumstance you'd ever have to make a 300ft shot with a pistol.
If you run out of ammo on your primary, you have time to reload.
If your primary is down, you won't want to be wasting pistol ammo liberally trying to engage people that far out.
If your pistol is your primary and you're trying to use it like a sniper rifle, then you should take a long hard look at the weapon you've chosen for that role lol