I agree with Tugex. An AT mine should disable, if not destroy any vehicle with one mine. Survivability would be the difference. Obviously a tank might only lose a track, crew 100% fine, where a hunter might be completely disabled, with heavy wounds inside.

If you zoom in while firing the littlebird, you can see there's actually a decent amount of dispersion. I think the real problem is rate of fire. The ROF is waaaay low on the AH-9. It's somewhere around 1/3 of the low ROF on the AH-6 from A2, and close to 1/7th of the high rate setting. 2 miniguns firing at 4,000 RPM should absolutely devastate infantry in the open.

I don't lose sound after I die and respawn, but my teammate can no longer hear me fire. Maybe the same bug?

I was able to repeat this yesterday in a mission I made. Normal difficulty, AI squaddie was prone next to me. I dropped a frag right on his back and ran. BOOM, he's still there. Dropped another directly on him, BOOM! I hear "wounded!". Dropped a third frag on his back and he finally dies.

Apparently the safest thing to do when a grenade is tossed at you is to dive on it.