Dunno, It worked for me in demo. Make sure you spam nades in quantity enough. Throwing one grenade and praying to blow the track off is likely as winning a lottery
Don't forget that those nades are shaped charges, so they have to(have to with capitals) be placed ON the target to make some damage. They're harmful as a kitten when not on something As for Ferdinand picking off your infantry with the gun, don't forget that it has an MG34 bow MG. Maybe MG is getting the kills while you're watching cannon fire .