Are there "alternate" weaponstats according to the core book for Mark of the Xenos out there? Or have we to convert them for ourself?

Maybe the new weapons are already adopted to the core book in Mark of the Xenos, because the number of damage dices seems slightly lower for most of the weapons.

What you're seeing are the revised weapon stats recently published in the Living Errata.

These were released a while ago to 1) Reduce the number of dierolls and 2) Apparently adjust weapon balance.

MotX was published late enough to have the errata incorporated into it.

The problem is that the alternate weaponstats are not integrated in Mark of the Xenos. Chaos Space Marines for example have the "old" values for Bolters.

Hmm, how odd. I could have sworn when I looked at Tau stats in MotX, the info for pulse rifles and so forth reflected the new values. I just assumed that the Chaos Marines did the same thing.

Now what? at the time, i had a look on the plaguemarines to see if they bore the new stats on their weapons. I saw the Astartes Boltgun RoF of (S/3/-) and though "oh, well, new stats then". But now I pay more attention, and see that is actually the only thing about new stats. Bolter pistols carry old stats, and most important... the Astartes Boltgun is all core book stats, excepting its RoF. That's crazy...

I imagine it's another case of **** editing on FFG's part, copy-pasting statblocks from elsewhere that doesn't feature the new weapons.

I'm constantly amazed by how despite the resources at their disposal and the prices they charge, they can;t edit their way out of a paper bag.

Another example is the Pulse Carbine of the Tau Pathfinder which uses the "old" stats. This is a minor problem for me because we already have the "alternative" weapons stats for this weapons. My problem is if the new weapons i.e. Rail Rifle are adopted to the "old" or "alternative" weapon stats.

FFG presents the stats in the errata as "alternative" not the "new or right" stats. Actually FFG has to give us weapon stats for every weapon for both versions.

As I mentioned my asumption is that the stats for the new weapons are adopted to the "alternative" stats because of the overall low number of damage dice except for heavy weapons.

Why is a Ork Shoota more dangerous in Deathwatch than in RT or DH and the Lasgun not? Is a Shoota a weapon which prefers to be used against Space Marines powered by the thirst for a good fight ?

Mormacar said:

Lascarbines and heavy stubbers got a jump in lethality in RT and Black Crusade ups the ante for a bunch of las weapons with their variable settings, so this is nothing new or something that's going away...

When using stuff from other games, you'll have to rely on your GM to decide which statlines should be used.