Warframe

What i did, and it's working with all the mastery achievements, is when you are close to level 30 with any weapon go to any mission and immediately when you hit level 30 close game. Repeat that process 5 times and you will earn the achievement.

You can check the progress on the achievement tab to see if it works :).

Update 19.5 Pistol and Akimbo Pistol Weapons List

Weapons in brackets are Variations on that Pistol, so there is a Lato, Lato Prime and Lato Vandal.

Single Wield
• Acrid
• Angstrum
• Azima
• Ballistica (Rakta)
• Bolto
• Cestra
• Furis (MK1)
• Kraken
• Kulstar
• Lato (Prime, Vandal)
• Lex (Prime)
• Magnus
• Marelok (Vaykor)
• Seer
• Sicarus (Prime)
• Sonicor
• Staticor
• Stug
• Tysis
• Vasto (Prime)
• Viper
• Atomos
• Embolist
• Gammacor (Synoid)
• Nukor
• Spectra

Akimbo wield
• Afuris (Dex)
• Akbolto (Telos)
• Akbronco (Prime)
• Akjagara
• Aklato
• Aklex
• Akmagnus
• Aksomati
• Akstiletto (Prime)
• Akvasto
• Akzani
• Dual Cestra (Secura)
• Dual Toxocyst
• Twin Grakatas
• Twin Gremlins
• Twin Kohmak
• Twin Rogga
• Twin Vipers (Wraith)

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Unlocking Weapons

19.5 Update
These Blueprints can be gained from finishing Junctions:
Furis (Venus Junction on Earth)
Kraken (Phobos Junction on Mars)
Cestra (Europa Junction on Jupiter)
Gammacor (Neptune Junction on Uranus)

Mk.1 Weapons you can buy for Credits from the Marketplace and provide quick replacements.

Akimbo weapons require 2 of that pistol, so if you want to make Akvasto you need 2 Vasto's, level a Vasto first and then use that and a fresh Vasto to make your Akimbo version.

Lot's of weapons require a Mastery Rank, but by levelling weapons you increase your Rank so this shouldn't be a problem, just make sure to Rank up regularly.
Check here for required Mastery Ranks or the Marketplace.

Prime Weapons require Void completion, often high level Survival/Defense 'Rotation C' drops. These are endgame. I use Primarch Prime Part Guide

Lots of weapons like Prisma, Vandal and Wraith Weapons are Limited Time exclusive weapons, some re-appear as Sortie or Week/end event rewards but some are gone, maybe for good. (Dex are Birthday weapons and they pop up once a year around April for free)

Anything else with an interesting alternate is probably a high level Syndicate Reward and requires MR12.

All in all, most are endgame weapons if you're just starting and want to finish off Pistols, then just stick with the vanilla versions, most take 12 hours and very basic Materials. Check the Marketplace for the easiest to build and any that can then be converted to Akimbo.

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Leveling weapons to Rank 30

The best way to level weapons is to play Survival or Defense missions and kill lots of enemies, then extract for the bonus exp, you'll get lots of weapon mastery whilst unlocking all worlds, doing alerts, unlocking other achievements and just playing the game. Remember to always swap for you next weapon and have one ready to swap.

Lots of Dark Sectors have Affinity bonus (+Shotgun), use a Warframe that supports you but doesn't really kill enemies so you rely on your weapons, being in a group spawns more enemies for more exp.

Elara on Jupiter is a great mission for Affinity, as the anti-moas spawn early and often, and they give a fair amount of affinity around 7-9x the exp of grunts.