Variant Weapon drops - info per Bastiaan Frank (MEA designer)

The design is meant to give players a small chance on getting weapon variations while finishing their base weapon list first.

Here is a more technical break down. Usually I prefer not do get into the details too much, takes away a bit of the magic, but I understand some people want to figure things out in more detail:

There is a pool for weapons
There is a pool for characters
There is a pool for weapon variants etc.

First you roll on rarity, after that it roles on the pools. Each pool has a chance associated with it (no i am not telling you what those are exactly, but variants is small as mentioned previously). Weapon variants can only drop after the base gun has reached rank 10. So biggy's statements(*) is 100% correct.

(*) This refers to:
[source]

Only additional info is: the pools each have fallbacks. The first fallback for the Weapon pool is currently the Weapon Variant pool. Which means if all your base weapons are done, you now have the initial chance of a weapon variant + the chance of a weapon to gain a weapon variation.

(me)
Example 1: I have 0 UR weapons unlocked. I buy a Premium pack that contains a UR weapon. Is there any chance of this being a variant weapon?

(Bastiaan)
1. You only get a variant of a gun, if the base is rank 10. So no, 0% chance on getting a variant.

(me)
Example 2: I have several UR weapons unlocked, but 0 of them at Rank X. I buy a Premium pack that contains a UR weapon. Is there any chance of this being a variant weapon?

(Bastiaan)
2. same thing

(me)
Example 3: I have many UR weapons unlocked including A, B, C which are Rank X. I buy a Premium pack that contains UR weapon. What are the chances it is a variant of A, B, C? What are the chances it is a variant of some other weapon D, E, F?

(Bastiaan)
3. Small chance on variant for A B C

(me)
Example 4: I have almost all my UR base weapons maxed (rank X) -- let's say just weapons Y and Z are at rank IX. I buy a Premium pack that contains UR weapon. What are the chances this is a Y or Z weapon rank X vs. a variant weapon version of one of the ones I already had at rank X?

(Bastiaan)
4. Same as 3.

(bonus example from Bastiaan!)
5. I have all my base weapons to rank 10. Now only variants drop if you would have gotten a weapon.