How do I calculate numbers of hits on a hord when shoting with say a bolter with special ammo (blast 2)?

Do I calculate blast hits(2 extra hits for blast 2) and rate of fire (say 4 hits, maximum for boltr) and ad them together for 6 hits with one extra for explosive damage =7 hits?

or

Is it blast 2 on every bullet: 4 hits x 3 (for blast 2) + 1 extra for explosive damage = 13 hits?

Or some other way?

thanx

Each hit is a Blast (2), not a hit + a Blast(2).

So, full hits from a bolter with Metal Storm are 4 x 2 + 1 (for X) = 9.

thanx!

About the "Each hit is a Blast (2), not a hit + a Blast(2).": So there is no difference between blast(1) and no blast at all when making damage to a hord?

Correct. Blast(1) is essentially irrelevant when it comes to Hordes.

Du you think it´s a typo, or should it be that way?

Blast(1) can be relevant vs a vehicle or similar (hitting both a weapon mount and the hull, etc.), but I'd say it's probably something that can be safely ignored in pretty much all situations.

I thought that the relevant math was 3 for a blast 2 and then 4 for the number of hits for a total of 12. You add the +1 for explosive to each hit is how I interpreted the text.

Explosive adds an extra hit not extra damage....so with a bolt gun and enough DoS you get 4+1 Hits

This has been answered in the Errata thread. It's (# hits x Blast rating) + 1 for X, so metal storm in a standard bolter is( 4 x 2) + 1 = 9.