I played a game today, against a guard playing opponent. He ran a list with 4 punishers and 3 normal Battle tanks, still a very fifth-edition list (He and I wrote it together, so I didn't really stop to think about what I was choosing too much. He had vendettas and a very small amount of infantry.)
I found that, despite the saturated armour on the field, the elysian fields of AV14, just ripe to be destroyed by rail guns, that they didn't manage to so much as blow up a single tank. I was taking two hammerheads for godsake, two! One had longstrike, and even longstrike only managed to glance twice and pen once - by god the pen wasn't even an explosion!
I got to thinking, what is a hammerheads actual chance of blowing up a land raider. How much potential do they actually have?
Well, let's think about it.
A normal hammerhead is 120 points, with BS4 and a single S10 AP1 shot at 72" range.
With a 67% chance, a 33% chance of penning and a 50% chance of then making the vehicle explode, we're looking at an actual chance of about 11% to make an AV14 side explode.
For AV13, this chance goes up to about 16%.
For AV12, this chance goes up to about 22%
For AV11, this chance goes up to about 27%
and for AV10, it goes up to only 33%.
Now sure, Longstrike does something to mitigate this issue, but not much.
Longstrike has a 83% chance of hitting, a 55% chance of penning, and as always, a 50% chance of making it explode. This means Longstrike has a 23% chance of making AV14 explode.
I don't know about you, but I won't be paying 170 points for a once-a-game effect.