Hm…i might be going about this all wrong but here is my thought process, if we are excluding jewelry from any calculation, then we have 15 melee weapons to 4 ranged ones as possible reds. To figure the chance of a single ranged when getting a red we simply note that 4 outa 19 options are ranged, in percentage that´s 4/19 ~ 0.21 =21% to get a ranged one each time you get a red weapon.
That in turn means you got a 79% chance of a melee weapon each time you score a red weapon with krub.
So how likely are 15 melee weapons in a row? I have kinda forgotten this stuff but as @Argonaut14 mentioned there is no system for getting something different from your last roll and every roll is considered a fresh one. Which if i am not mistaken that means you can calculate the chances of 15 melee rolls in a row by simply multiplying the probability of a repeated case with itself once for each time you do it.
Because i am lazy i will state that the chance for a melee roll is 80%, or 8/10, and so to figure out the probability for 15 in a row you just take that 80% in fractional form, 8/10, and multiply that by itself 15 times.
8/10 ^15 = 0.035 = 3.5%
ehm…and this i think should mean that the chances of you pulling 15 melee reds in a row is 3.5%? Which in turn would mean that getting a ranged one somewhere along the way is the remaining % to hit 100 which is 96.5…
I may have forgotten a bit too much of this stuff, it doesnt seem quite right somehow