Apologies if I missed a discussion on this already:
Thoughts on Mummu Jacket +2 vs Meghanada Cuirie +2 for Armageddon AM3 sets (no Triple Shot)?
I recognize the recommended sets say Meghanada but I would think prioritizing crit rate over crit damage would be better under AM3 (more crits > harder hitting less frequent crits?). Same logic with Kecks vs Darraigner's Brais.
Crit damage is a big DPS improvement over similar amounts of crit rate, which is why Meg+2 body is typically recommended over Mummu+2. (
plus, if you're in an uncapped attack situation, Meg+2 adds Ratk+46 and a little more STR)
The legs are a harder call. Darraigner's will give you stronger DPS if you can hit, but they seriously lack Racc. RNG can usually deal with that, but it's a bit harder for COR (and as you noted, you're running into some Racc issues on higher end Ambu) so in your situation you probably do want to go with Mummu+2 for the Racc+45 and Crit rate +7% when AM3 is up (and maybe use Adhemar when AM3 is down and you want more STP). Plus, don't forget to account for the additional AGI+8 from another piece of Mummu set bonus, which is going to further help your Racc and crit rate.
Neck/earrings you're aware of, but yeah, Iskur Gorget and eventually working toward better earrings is the thing to do. Relative ease of acquiring Enervating Earring if you can get your group to do a 5/5 Vagary run (or maybe just get lucky on Perfidien) would be a nice improvement for you and let you drop Volley.
If you really have to swap out a ring due to Racc issues, you could drop the Begrudging in favor of something like a Cacoethic+1 (or Haverton/+1 if you happen to have that) for a pretty large chunk in one slot. But ideally, you're able to pick up the ranged accuracy elsewhere like legs, improved earrings, a neck swap (see below), etc.
Similarly, lacking Iskur, you might look at swapping out Ocachi for something with more Racc, if hit rate is becoming a problem. Marked Gorget is a pretty good alternative, giving up Ratk+10/STP+2 in exchange for Racc+15/AGI+3.
I prefer gearing for store tp over crit so I can shoot less and ws more. =) So personally just looking at your set I would use the adhemar hands and legs +1 both will have far superior r.acc and store tp. But that's just my opinion
You might not be considering that Lunafreya is asking specifically for an Armageddon. Ranged Empyrean weapons take WAY more advantage of crits when AM3 is up. If using a good crit set, it's not terribly surprising to see half of your crits (AM3 50% proc rate) landing at almost WS-like damage, sometimes multiple times in a single attack round when Triple Shot is up. That being the case, shooting with Armageddon is a bit of a unique case, since the ratio of white damage to WS damage is going to be substantially higher than any other COR setup. Maximizing that requires an approach that differs a bit from the more standard rationale for other weapons, which would lean more toward STP.