Okay, am I reading something wrong, or are there some errata here?

The burn effect is pretty powerful. A basic flame projector has base damage 8 and burn 3, so for only two 2 advantage you can deal another 8 damage x 3 rounds = 24 damage. Granted, the target does get a chance to put the fire out, but this still seems like cheap damage to me.

But here are my queries:

The under-barrel flame projector mod p. 102 has dam 10 and burn 5 (that's going to give you up to 50 extra damage). Does it make sense that this weapon mod is way more powerful that the stand alone flame projector?

Then check out the stats of the master bounty hunter on p. 400. His modded rifle has a flame projector with damage 13, burn 5. This isn't even possible with the modding rules. But also, imagine your lucky PC doesn't manage to roll the fire out: for a measly 2 advantage, they're taking a bonus 13 damage every round for 5 rounds.

What am I getting wrong here please?

His modded rifle has a flame projector with damage 13, burn 5. This isn't even possible with the modding rules. But also, imagine your lucky PC doesn't manage to roll the fire out: for a measly 2 advantage, they're taking a bonus 13 damage every round for 5 rounds.

What am I getting wrong here please?

The Damage of 13 includes Deadly Accuracy. The Damage should be 10 + 3 because this extra Damage would not apply to the Burn quality, only to the initial hit.

Ah, that is good to know. Thanks. What about the issue of the under barrel being more lethal than the standalone weapon?

Suppose it's reasonable once cost is compared. But seems odd.

It also has a much lower blast, so you could probably rationalize it as the underbarrel launcher delivering a much more concentrated burst of flame, this would also handily explain the higher burn rating, most of the fuel is going right into Joe stormtrooper's face instead of the more general "kill' em all" of the stand alone weapon.

Yep, okay. I like that.

Also keep in mind that:

1) the Blast quality requires 3 Advantage to activate instead of the usual 2, and

2) Burn effects can be cancelled with an Average: Coordination action.

Blast can be activated for 2 if you hit, the 3 is for activating it even if you miss.

2) Burn effects can be cancelled with an Average: Coordination action.

Note that a target takes the damage from Burn before their action, so it's tricky to not take at least one additional instance of damage if Burn activates.

2) Burn effects can be cancelled with an Average: Coordination action.

Note that a target takes the damage from Burn before their action, so it's tricky to not take at least one additional instance of damage if Burn activates.

If you are alone it is tricky to avoid, but if you are in a group than if and when the others act and get advantage, they can (and probably should) use it to grant you an extra action which you can then use to try to put it out.

2) Burn effects can be cancelled with an Average: Coordination action.

Note that a target takes the damage from Burn before their action, so it's tricky to not take at least one additional instance of damage if Burn activates.

Not that I disbelieve you but where does it say that? I do not recall reading either of those rules. Book & pages please?

p. 155 under the Burn definition. It says it's applied at the start of each target's action, so before they get to stop, drop, n roll.

Still, a single extra round of burning is a lot better than five extra rounds of burning.

Okay, am I reading something wrong, or are there some errata here?

The burn effect is pretty powerful. A basic flame projector has base damage 8 and burn 3, so for only two 2 advantage you can deal another 8 damage x 3 rounds = 24 damage. Granted, the target does get a chance to put the fire out, but this still seems like cheap damage to me.

But here are my queries:

The under-barrel flame projector mod p. 102 has dam 10 and burn 5 (that's going to give you up to 50 extra damage). Does it make sense that this weapon mod is way more powerful that the stand alone flame projector?

Then check out the stats of the master bounty hunter on p. 400. His modded rifle has a flame projector with damage 13, burn 5. This isn't even possible with the modding rules. But also, imagine your lucky PC doesn't manage to roll the fire out: for a measly 2 advantage, they're taking a bonus 13 damage every round for 5 rounds.

What am I getting wrong here please?

Soak, it applies to every instance of the damage, making it a lot less lethal than you are imagining.

Here's a related question. Does Burn stack?

Say I activate Burn on a target, then at the start of his turn takes Burn damage.

On my next turn, I hit him again and have the Advantage to reapply Burn.

At the start of his next turn will he take Burn damage twice if both applications are still going?

If not; Would the applications stack if applied from different sources (One PC throwing a firebomb and another using a flame projector)

Good question. At my table, I would take the higher of the 2 sources.

If I were to allow both to stack, I will still only allow one action to remove them both, but stacking burn should feels wrong.

I wouldn't allow them to stack in the case of the flame projector. Only so much of the fuel can be exposed to oxygen, so it can only burn at a set rate. The flailing and screaming that normally occurs when a panicked person is lit on fire will also tend to fling the fuel away from them. The flung fuel will burn, but not on the target so can be ignored (barring interesting uses of triumph and despair of course).

Only the most recent use of burning should apply.

I'm AFB right now, so I don't know page numbers and I might be mixing effects... But if I recall correctly, when a second Burn quality is activated while a first is still enduring, the duration is stacked. I.E. I hit you this round for burn 3; next round, (you have Burn 2 remaining), I hit you with Burn 3 again. You are now at Burn 5 (remaining 2 + new 3).

As for different sources of damage (and thus varyingdamage amounts) I don't recall seeing any mention of this. My house rule would be one of three ideas (pending the situation)...

1) the Burn damage is now the higher of the two for the duration of the combined two (or until put out). This would be good for if both sources are fire.

2) combine the damage for the combined duration. This could be for fire burns ON TOP of chemical burns.

3) keep track of the round numbers and burn qualities remaining and apply the damage to the appropriate burn turns (bear with me, that sounds stranger than it is). So if I hit you for 5 damage, then activate Burn 3, then my buddy his you with 10 damage, Burn 5... your first 3 turns of burn would do the 5 damage, the next 5 turns would do the 10 damage. This would be for the RAW fanatics that love to abuse rules to the max.

To the OP, the flavor text for both items might shed some light as well. The under-barrel attachment's main purpose of design is as a weapon , whereas the flame projector's is not (but, as the text indicates, it works just fine for burning flesh and bone).

And to the question of how to handle "stacking" of the burn quality, I can't see anywhere that it's called out in the CRB. But yeah, I'd stack the duration and then use the higher of the two damage values to determine damage over the duration.