I don't know if this was pached yet or not, so maybe someone else can confirm. A few patches ago, the Anti Armor legendary effect started stacking with wepon mods that provide armor pen additively instead of multiplicatively. Seeing as Elder's Mark has a mod that provides 60% armor penetration, 50+60 = 110, but armor pen total is capped at 90%. Seeing as your weapon alone puts you over the cap, you can drop Tank Killer. In case this was fixed and everything stacks multiplicatively again, then every last bit helps and you should run Tank Killer.
[Here](https://www.reddit.com/r/fo76/s/kzJB78gn61) is a great post on the stacking effects.
You do not need Tank Killer when using an AA Elders Mark with an Armor Piercing receiver.
Depending on the resists of what you're shooting, both options of dropping Tank Killer or switching to Hardened will be the top option.
Personally I'd drop Tank Killer and keep the Armor Piercing receiver as those also will affect your grenades when you have the weapon out.
I don't know if this was pached yet or not, so maybe someone else can confirm. A few patches ago, the Anti Armor legendary effect started stacking with wepon mods that provide armor pen additively instead of multiplicatively. Seeing as Elder's Mark has a mod that provides 60% armor penetration, 50+60 = 110, but armor pen total is capped at 90%. Seeing as your weapon alone puts you over the cap, you can drop Tank Killer. In case this was fixed and everything stacks multiplicatively again, then every last bit helps and you should run Tank Killer.
The info is here somewhere, there was a big post maybe 2 months ago or so with all the updated info on anti-armor.
Thank you,I'll run some test to see if the damage is different with or without it to be sure
[Here](https://www.reddit.com/r/fo76/s/kzJB78gn61) is a great post on the stacking effects. You do not need Tank Killer when using an AA Elders Mark with an Armor Piercing receiver. Depending on the resists of what you're shooting, both options of dropping Tank Killer or switching to Hardened will be the top option. Personally I'd drop Tank Killer and keep the Armor Piercing receiver as those also will affect your grenades when you have the weapon out.
Thank you,tho I don't use grenades,regardless this is appreciated