Which requires specialized equipment that does not appear to exist in the Battletech Universe.
Though granted, I guess a veteran gun crew might be able to prepare a volley like that if they had plenty time to prepare and knew exactly what and where their target was.
BT artillery already allows for artillery guns at different distances from the target hex to have their shells take different flight times, with no change to the shots per ton. IIRC the flight time is 1 turn for every 2 mapsheets of range, so if a Long Tom is 20 mapsheets away, the shell will take 10 turns to arrive. If that same Long Tom is 4 mapsheets away, the shell will take 2 turns to arrive. No notes about needing to change the ammunition, just fire and hope it lands near.
As for specialized equipment, we use it today with mortars. Adjust the angle, adjust the number of 'augmentation charges' added per shot, and you can get different muzzle velocities. Different velocities at different angles when done right mean multiple shots landing at nearly the same time.
Now if the shells are fixed charges, then the distance is determined solely by gun angle. You can get a second shot by angling the gun closer to vertical, but that will take 10 turns to arrive, and the lower angle will take the 1 turn per 2 map sheets flight time.
For sweet spot of multiple charges, check the ranges chart for the British
81mm L16 mortar. If a target is 1700 meters away, there are 5 charges that allow a shot to be dropped on the target, allowing for changing the firing angle and making sure the math is right.
So we'd need a message from the mods to determine if adjusting the firing charge is allowed for artillery (similar to adjusting the number of bags for the 16" guns on the Iowas), or if the cartridge is a single unit.
But that is an interesting idea for Arrow IV though. Have the missiles circle the battlefield, then on turn Y all the missiles in orbit (plus the one arriving that turn) look for the TAG light (or the target hex).