Hello there,

As per Wiki:

• Kuva Karak: Shorter reload time, lower recoil, and greater accuracy.
• These weapons have a max rank of 40. To obtain the maximum rank, the player must polarize the weapon five times, with each Forma increasing the maximum possible rank by 2 (in a similar manner as the Paracesis).
• All Kuva weapons deal innate elemental damage in addition to physical damage. The amount of this damage is random, ranging from 25-60%, while the type of element is determined by the Progenitor Warframe, as per the table below:

According to the above I added exactly 5 forma to this weapon, so we can obtain Mastery Points from it.

In this case I recommend to pick Heat as an elemental.

Some info about Kuva Karak:

• High critical chance
• Above average critical multiplier
• Very high status chance
• High fire rate
• Extremely high accuracy and negligible recoil
• Innate 0.2 meter punch through

This build will gain much more from combining your Warframe with Sentinel which will carry Sentinel Weapon with Vigilante mods on it. Even if your Sentinel dies, the Set Bonus will remain. Four Vigilante Mods gives you 20% chance to enhance Critical Hits from Primary Weapon.

Enjoy, THeMooN85