I have a bunch of seals to burn and i want a PCA so i guess i'll be keeping track of how UO goes and how long it takes for me to drop it so other ppl that plan to farm it have a kind of reference.
(I will omit the 100% drops, namely mercury and hecteyes eye)

EDIT: These orbs were all used AFTER the latest bcnm changes.

Orbs:

1. • Yellow Rock
   • Fire Spirit Pack
2. • Scroll of Erase
   • Grudge Sword
3. • Peridot
   • Scroll of Ice Spikes
4. • De Saintre's Axe
   • Yellow Rock
   • Pearl
5. • Mutilator
   • Buzzard Tuck
   • Pearl
   • Scroll of Erase
6. • Scroll of Utsusemi: Ni
   • Phalanx
7. • White Rock
   • Scroll of Erase
8. • Yellow Rock
   • Scroll of Erase
9. • Purple Rock
   • Black Pearl
10. • Scroll of Refresh
    • Scroll of Refresh
    • Black Pearl
11. • Raifu
    • Peridot
    • Garnet
12. • Tourney Patas
    • Grudge Sword
    • Blue Rock
    • Scroll of Fire spirit
13. • Green Rock
    • Ametrine
14. • Scroll of Refresh
    • Tourney Patas
    • Gold Beastcoin
    • Sphene
15. • Mutilator
    • Black Rock
    • Scroll of Absorb-STR
16. • Scroll of Refresh
    • Mutilator
    • White Rock
    • Scroll of Fire spirit

If it helps your data I went 1/1

a whole year ago my friend and i averaged 1/10 for each of our 4 chars

that's all i've got. dmitri i think got his 1/1 when i ran with him 6 months after.

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I've run this quite a bit for friends and I'd say 10%-ish is probably correct. My luck has been a bit better as I have seen 4 drop in def. less than 40 runs, but the 10% number would be consistent with the retail droprate.

Edit- actually I've seen 5 drop now that I think of it. I've def. been above 10% but I don't have an exact number of how many runs I did.

We went 2/3 runs back in.... April or so. Pretty lucky!

I forgot to mention: i know in the past the drop rate was higher than it was supposed to be, after the BCNM drop rates were fixed by nas i don't think anyone farmed this bcnm extensively, gonna do 3 more runs today and update the first post.

We went 1/3 less than a week ago and got a scroll of Ni as well. So 1 Amulet, 1 Ni and trash in 3 orbs.

I'm 0/15 personally and 0/45 on runs participated in. all runs were between december 2018 and ~march 2019.

this is as far as I can tell abnormally unlucky. probably balances out all the 1/1 an 1/3s people are reporting :P

I've heard everything from 1/1 to 1/30 and beyond. I lost count myself, saw two mates get their PCA and rotate out of my UO groups, before I got mine on my main. Gonna start doing it for my alt soon. It is great kite training for rdm, especially with the fucked up pathing. Embrace the grind.

Personally doing the 3blm strategy and it has worked ok so far, we have an average clear time of under 5mins but we don't do more than 3 runs/day because we use 2h to be safe from resists.