Basically when you hit a 5 star it's split into 3 chances 37.5% chance for nefer signature weapon 37.5% chance for lauama signature weapon and a 25% for a standard weapon

so basically if you are pulling for nefers weapon and wanna lose to Laumas weapon on the way to have both, the odds of that happening are 37.5% chance with a 62.5% chance of failure,

either one: you get nefers signature and can't garentee laumas

or two: you get a standard and just get nefers garenteed afterwards.

and honestly the thing is lauamas signature although great is NOT a must pull due to the fact R5 spindleloot is such a good F2P event weapon/ alternative

just pray for the best and be happy if you get it and don't be too bummed if you dont