Finally, the dual-pistol expert stance has been released in v8.6.0! It can be acquired with Symbol of Pisces. Click on image below for large view or see 언리미티드 샷 (Korean Screen Board). Discuss at IAH forum topic Expert Pistol Stance: Unlimited Shot.
For Chinese translation of stance/skill bonus, see [Expert] Unlimited Shot 無窮狙殺. Briefly, its normal attack is 4 shots per cycle. The Lv.25 stance bonus are Accuracy +12, ATK Speed +12%, Evasion +5, and Penetration +17. The stance is available to musketeer and Garcia (aka Gavin). Lv.11 Reload Action skill grants Evasion +22 and ATK Rating +1. It also refreshes all cool-down times.
See also the embedded video below 언리미티드 샷 by Riel0113.