The NS-357 IA has several key differences to the Underboss. Firstly, the IA sacrifices 40 RPM as compared to its parent gun. Secondly, the IA fires two rounds per shot dealing 250 damage each, as opposed to the Underbosses' single 375 damage bullet. These two rounds fire in a tight cone shotgun-style, with greatly improved hip accuracy as compared to the Underboss. Finally, the IA has a much harsher damage drop off, starting at only 2 metres.
The NS-357 IA is one of three weapons currently available for purchase using A7, alongside the NS-44L Showdown and the NS-AM8 Shortbow. All three weapons are purchased for 4,000.
It is possible to get both Ribbons and Medals for using the NS-357 IA. Each Ribbon is a standard reward for achieving a set amount of kills with the NS-357 IA. Medals relate to how many overall kills you have with the NS-357 IA.
The pistol name is a reference to "The Instant Action Podcast", and its description to podcast host — Mark "Deringer".
Alongside the NS-44L Showdown and NS-AM8 Shortbow, the NS-357 IA was previously obtained randomly from winning alerts. The player would need to have participated in at least 90% of an alert, own the related weapon, and succeed against a "very, very, very low" chance of receiving the weapon. This was changed in the Escalation update.