How does the High Impact Reserves perk interact with the Extended Mag mod?
I have a weapon which has High Impact Reserves, and I've placed an Extended Mag mod into it, boosting it's rounds from 36 to 42.
Will this give me more high impact rounds in the magazine?
Solution 1:
The Hight Impact Reserves always works like this:
The bottom half of the magazine deals extra damage, increasing as you go deeper. The final round in the magazine deals 30% extra damage.
Thanks to the research people did on Reddit (thread in question), we know that it combines with Extended Mag, but the damage cap is still at 30%:
High-Impact Reserves tops out at 30% extra damage, regardless of how many you have in the magazine. Did some testing with a Tigerspite.
Starting at 33 rounds, High-Impact Reserves will kick in when there are 16 rounds in the magazine. It hits for 108 crit damage against a Trostland level enemy on the final round.
With a Backup Mag mod, we start at 39 rounds. High-Impact Reserves kicks in when there are 19 rounds in the magazine. It also hits for 108 crit damage against a Trostland level enemy on the final round.
The benefit is that you'll see increased damage longer. Have 50 rounds? 25 will deal increased damage. Up that to 100? 50 will deal increased damage. The final round will always be the same, but you'll do more damage per magazine the bigger it is.
Solution 2:
While I cannot find a concrete number, these patch notes indicate that the perk provides a damage buff over a percentage of your magazine. Thus, logically, it would seem that a larger magazine size would give you more bullets with a damage boost as well.
Some players are theorizing about the perk, stating that there's a larger increase towards the end of the magazine (e.g. the first bullet with a damage boost provides a lower damage bonus than the final bullet in the magazine). There is some information about it in this reddit thread. In this thread, they also assume that the bottom half of the magazine starts giving a damage boost to each bullet.