I've tested this in VR a few times. Equip the Spiker and switch to the charged shot firing mode. This allows you to deal light damage to heavy vehicles. Charge up a shot, then switch back to the standard firing mode while still charged up. You will find that until you reload, the Spiker will still be able to deal damage to heavy vehicles.
Can confirm that it works, pressing B while charging up releases a standard 2-shot burst, dealing armor piercing damage. Subsequent shots in that mode (until the clipis empty) also deal armor-piericing damage.
I haven't done damage testing, but I would assume comparable to a clip of fully charged shots in the secondary fire mode. The big thing is I'm fairly certain the bug allows you to use the two-round-burst fire mode's faster projectile velocity, as opposed to the charged shot's slower speed. I was just bringing the bug to everyone's attention. We should be working together to create a comprehensive report.
