The Tech-Priest may use this mechadendrite as his Reaction for the
round or as a Half Action Attack on his own turn, but it can only
be fi red once per round. The Tech-Priest uses his full Ballistic Skill
for the attack.

I put a bolter on one, and a las pistol on another one.

Can I attack with each one? If I had 4 could I attack 4 times meaning, does a mechandrite GIVE me a half action attack or do I have to use my own? (wording: i can use the mechandrite as a half action attack)

After all is done that round, can I use my unused reaction to shoot (if I haven't used the mechandrite before)?

vogue69 said:

It doesn't "give" a half-action attack. If you chose to fire your ballistic mechadendrite as an action as opposed reflex firing it as a reaction to something, then you may do so, but it will take half and action and be considered a Standard Attack for the purpose of determining what else you can do that round. If you fire the mechadendrite in such a fashion, you will only be able to fire one and you will not be able to preform any other Standard Attacks.

If you have more then one Ballistic Mechadendrite, then one can be fired as a reaction and one can be fired as a standard attack. Unless you have some talent that gives you more then one reaction per round, firing the mechadendrite as a reaction can only be done once no matter how many bs mech's you have attached. Further, firing one as a reaction can not be done if you have already used your reaction to do something else like parry or dodge. Conversely, if you use your reaction to fire the mech, you will not be able to use your reaction action to parry or dodge (unless you have Step Aside or Wall of Steel).

As a reaction is, well, a reaction to something, you can not save it for the end of the round. You either react to something by shooting or you don't. Deliberately firing it takes half an action. As such, I would say you can only use your reactive firing when you have something to react to and only at that moment. You can't "save" it to the end of the round or cash in on an unused reaction, but that's just my interpretation of reactions.

so the only tactic is then: grapple your enemy and shoot him with a reaction? a mechandrite doesn't give you any advantage in combat except attack with a reaction?

vogue69 said:

I'm not entirely sure this is the way it works but here's how we deal with it. You get to fire the mechadendrite once per round(besides all your other actions) but you lose the ability to dodge or parry for that round. So you trade your reaction for a shot with the mechadendrite, simulating you concentrating on hitting the target and therefor not being able to get out of the way.

There are also a few problems with mounting a bolter on it, the rules don't support that. And unless you have the machinator talents you are limited to the standard las-version from the corebook.

The Machinator Array (Talent) description on page 70 should
say the following in its last sentence: “Thanks to your additional
augmetics any Ballistic Mechadendrite you possess may mount a
single pistol weapon or one-handed melee weapon rather than the
usual compact laser design (you must have the appropriate Talent
to use it).”

The Ballistic Mechadendrite on page 154 states: “As a reaction
the Tech-Priest may use this mechadendrite as if it were his off
hand, but suffers no penalties to hit.” Instead it should read: “The
Tech-Priest may use this mechadendrite as his Reaction for the
round or as a Half Action Attack on his own turn, but it can only
be fi red once per round. The Tech-Priest uses his full Ballistic Skill
for the attack.”

If used as a reaction, then of course you do not get your dodge or parry, but it can be used anytime. Just because you arn't reacting to something directly coming at you, doesn't mean you can't shoot at something that is about to attack a fellow player or person of interest. etc. All the reaction rule (To me anyway) means is that you forgo the right to get out of the way to slide in one extra attack.

For an example, my machinator myrmidon will either use his bastard sword or breacher to attack (standard attack, half-action), half-action aim (+10 to next hit) then use my reaction to shoot the irontalon ballistic mechandendrite.

so the only tactic is then: grapple your enemy and shoot him with a reaction? a mechandrite doesn't give you any advantage in combat except attack with a reaction?

I don't quite know what about shooting with up to three weapons per round can be considered "only".

can you parry with a melee mechandrite? (secutor)

Assuming you spend the reaction to do so, I wouldn't see why you couldn't.

Generally though, I prefer parrying with the Utility Mechadendrite's blade as it has (for whatever reason) the Defensive quality.

Cifer said:

I love the Utility Mechadendrite - it has saved me many times much to my GMs chagrin. That was my main method of parrying until I became a secutor and now wield a power sword on my Ballistic Mech.

Yes you can fire both Mechadendrites in the same round, no problem.

One will cost you your reaction while the other will cost you a Half Action leaving you with a half action to move or do whatever non combat related thing you were doing.

The "cookie" you get for being able to fire the ballistic mechadendrite as either a half action OR a reaction in a given round comes from the basic Adeptus Mechanicus mindset and training. When attacked in melee they tend to parry, either with a held weapon or a utility mechadendrite. When shot at.... they tend to get hit. They are tough, armour-plated bastards in the first place, and often burdened by many unbalancing and bulky implants and tip the scales in shocking amounts sometimes. From a game standpoint, they tend to have questionable Agility attributes and are not trained in Dodge skill. So for the sake of argument, our Techpriest hero has a BS of 43 (1-2 advances), an Ag of 26 (no advances) and lacks the dodge skill. Someone shoots at you with a lasgun or some other implement of less-than-total-disintegration, do you A) spend your reaction on a dodge of 13? OR B) spend your reaction to shoot the wretch with a cyber-tentacle mounted laspistol while contemptuously continuing on with the task you were working on as if he was no more than an insect?

If I am a Techpriest I know the answer I would go with.