Runaway Gun
This really is into the realms of "it couldn't happen" but if you converted speed to height in something without an off boresite facility, you haven't really solved your problems. You still need to get nose on to the tgt to aquire and with something as "cold" as a Herc you need to get pretty close (this also prevents the Herc with its good rate and radius of turn from getting nose on). This leaves you in your Mighty Hunter with a good bit of nose down against a target at very low altitude - best you get your LSJ on!
The Herc is not the easiest of beasts to shoot down with a 9L, radar laid guns is a different matter.