Probably the 300 is going to give you better performance when it comes to accuracy.
I sure am a fan of the 3030 as a nice lever gun though.
a 30-cal rifle or sniper rifle. closer to 30-cal
No such thing.
No.
Barrel length is usually 20 to 26in, but can be custom depending the environment.
100-300 or so
Your rifle was likely made by Mossberg as their model 810. In general, these are not long range sniper rifles, but were well made, reliable hunting grade firearms. If the bore and the muzzle crown are in good shape, the rifle should be capable of better accuracy than the average shooter is capable of- an adequate 300 yard deer rifle.
The basic Moisin-Nagant 91/30 is about $100. A TRUE original sniper version is about $600, but there are a lot of copies. Beware of fakes.
About 300 meters, depending on the rifle, sights, ammo, and skill of the shooter.
The Dragunov (note corrected spelling) sniper rifle is in caliber 7.62x54mmR. This is the same caliber at the Moisin-Nagant 91/30 rifle.
50-300 usd
Without knowing your intended use, there is no way to answer.
The cartridge itself is. It has a flatter trajectory than the .308. As for the rifle itself, it all depends on the tolerances and build quality.