I've been carefully reading the Werewolf the Apocalypse 20th Anniversary rules and running some numbers. My assumptions, based on the accepted answer to this question and my own answer to the same question, are that, on average, you get a certain number of successes for the number of dice rolled:
Difficulty
Successes 6 7 8
1 3d 4d 5d
2 5d 6d 9d
3 7d 9d 14d
4 9d 13d 18d
5 12d
Note that deviation is +/- 1 for up to 6d and +/- 2 for 7 or more so there is quite a wide variety of outcome.
Now assuming that the shooter has Dex 4 and Firearms 5 for a 9 dice pool, that the target has Stamina 3 to Soak the damage, and that Dodges and Armor are not in effect we can work out the following options.
Single Shot
- 9 dice to hit gives 4 successes and thus +3 dice for damage
- 30.06 rifle does 8 dice damage upped to 11 dice from the to hit bonus which gives 4 successes for 4 levels of damage
- The target then Soaks 1 level of damage ending up with 3 levels of damage
To do 7 levels of damage to incapacitate will take at least 3 turns which gives plenty of time for changing form and regenerating and thus it's reasonable to assume that it is not generally possible to kill a Garou with a normal rifle, let alone a smaller firearm, regardless of whether the damage is lethal or aggravated damage. So how about trying those special manoeuvres?
Aimed Shot
- Add 1 dice for aiming and 2 dice for a scope
- 12 dice to hit gives 5 successes and thus +4 dice for damage
An aimed shot is better but it's only going to add a level of damage if you're lucky. A fully aimed shot (3-4 turns of aiming) adds another dice of damage.
Aimed Head Shot
- Add 1 dice for aiming and 2 dice for a scope
- 12 dice vs difficulty 8 gives only 2 successes and thus +2 dice for damage after including the +1 for a headshot
So an aimed head shot is no better than an ordinary shot unless the StoryTeller gives some sort of bonus for it.
Three Round Burst
- Add 3 dice for 3 round burst
- 12 dice vs diff 7 gives 3 successes thus +2 dice for damage
A three round burst is actually worse than a normal shot for our shooter! This is partially due to the way I have calculated the dice vs successes chart above, for certain cases it is better to shoot a three round burst.
Full Auto
- Add 10 dice for full auto
- 19 dice vs diff 8 gives 4 successes thus only +3 dice for damage
- But the only full auto rifle is the Assault Rifle with 7 dice damage which gives 10 dice damage in total so only 4 successes again
In conclusion, unless I'm missing something, the rules for firearms seem to be kind of feeble and designed to be in line with melee damage. Using manoeuvres does not improve the damage done because the difficulty increase usually outweighs the bonus dice.
The optimal way to do damage with firearms is to simply increase the dice pool without increasing the difficulty. Aim the first shot, then keep taking single shots.
If you want firearms to be deadly to Garou then some house rules need to be added to make firearms more deadly and allow burst fire, full automatic, and head shots to do significantly more damage or have some sort of special effect. However what those rule should be is definitely out of scope for this question.