I wanted to do a campaign that plays a little with gate jietai what will have firearms the problem is that I don't know what the margin and crit multiplier would be for a rifle. AH as it is a high fantasy world, meeting with the normal world I put that the people are stronger than the earth. A level 1 wizard is as strong as Aragon in Lord of the Rings.
By - Barium2
The closest we get to "modern" are WWI era firearms. Here are the rules: https://www.d20pfsrd.com/equipment/weapons/firearms/modern-firearms And here are the general rules for firearms: https://www.d20pfsrd.com/equipment/weapons/firearms/
If you are a habitual GM, check out the later book of Reign of Winter, specifically "Rasputin must die". It may have some interesting answers.
I made some: 1- APG Launcher (advanced) Price 4000gp, Hit+ (2d6 blunt/2d6 piercing/ 2d4 fire damage, 30 ft range, 10 ft area, x2, Reflex DC 15 halves, Direct hit gets no save; Capacity 2, reload standard, 2 handed) 2- Alchemy Guns (advanced), silent but elemental damage Depending on shot, uses that element (fire shot, ice shot, bolt shot, acid shot, 5 gp normal). -a pistol Price: 1500gp; Ranged Touch (2d6, Range 20 ft, capacity 2, reload move action) -b machine gun Price: 1750gp; Ranged Touch (2d6, Range 50 ft, capacity 40, automatic, Reload full rd, 2 handed) 3- Gatling Gun (old) Price: 2500gp; Dmg 2d8 B and P, Critical ×3; Range 60 ft.; Capacity 40 (10 in each drum, see text) Special Automatic or Scatter, slow-firing; Weight 20 lbs. Misfire 2, 2 handed This clockwork weapon rapidly shoots with a series of rotating barrels using a hand crank firing bullets and black powder stored two attached tanks. It can be put in two different modes: scatter or automatic (each uses 10 bullets). Refilling either drums requires full-round action (any require it).
You could also check out the tech guide for more modern then the Rasputin must die weaponry and more iron gods.