Can you post a screen shot of the gun?
I never really noticed before, but as you describe it, the rolls will stack(Verified with a 6.2 Crit before modding), but the mods use the base. The only way to verify it would be to remove the Tier IV and use a Tier III.
If they stack, then = x7.4 for Tier IV and x7.2 for Tier III or in your Math x7.0/x6.8.
I've sold the gun for a ridiculous amount of scrip though, so I won't be able to test it myself.
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GT: flavorblisters
IGN: Critical Errors / Liquid Sugar / TrionCelebrity/ MarketCrusher
All bonuses apply to the base only. Trick verified that a couple of livestreams ago.
If you add them together first and then apply to the base, that's not stacking them.
The mod was for 20%. So you had a 55% bonus before the mod.
4.0 x 1.55 = 6.2
so if my vbi ar has a 1.15 and 1.20 and a barrell for 1.15 and i have skill level 20 what should the crit be because mine says 2.4 like the other gentlemen said was the cap