Different weapons have various effective ranges. Standard machine guns are effective around 1200 meters. Your reticule will change to circle when you’re in effective range to your target. You have to take note of this distance especially in Hard difficulty since your ammo will be limited. Standard Missiles have a lock-on range of 2000 meters while other SP weapons (with lock-on feature) will have their own ranges as well.
For unguided weapons such as normal bombs and rockets, you’ll be able to see their blast radius instead. Bombs are ideally dropped at high elevation for you to see the blast zone. Dropping it too close will also damage your aircraft. You can also increase the blast radius a bit by equipping the corresponding upgrade part.
Certain SP weapons like electromagnetic projectiles and tactical lasers will always have exceptional ranges and can be fired on a target even when you haven’t selected it yet. These weapon ranges can be further enhanced by specific upgrade parts.