I had a real problem my first time through the game because I built a hunter/sniper character and wanted to use certain guns through the game, many of which failed for me in VATS. I did some fairly extensive testing with different guns under different conditions and this post is about what I found.
The VATS accuracy bug affects all revolvers and some rifles.
I did extensive testing here, when I tested my character had strength 7 (sufficient for all guns mentioned) and also I have the Character Creation perk of Slow Trigger that gives a 20% accuracy bonus with guns and energy weapons, but you fire 20% slower. (As an additional test I also created a new character without the Trigger Perk and was able to re-test revolvers, and the results were the same.)
The bug is sort of two-fold:
I will qualify two terms I use here:
(1) By "VATS accuracy" I mean what VATS tells me my chance is.
(2) By "REAL accuracy" I mean what I measured over time firing hundreds of shots at all ranges and various conditions from grassy to flat open ground.
Test 1: Revolvers in reality hit about 1 time in 50 for me using VATS. That's right: in VATS, using any revolver (.357, .44, Hunting Revolver) my REAL accuracy was approximately 1 shot in 50 or about 2%. This remained true at all ranges and in all conditions, whether my VATS accuracy said 95%, 80%, 50%, or whatever, my REAL accuracy was always about 1 shot in 50. And in the same fight after missing 24 times in a row with a revolver (typically 3 reloads) I would test by switching to a pistol and my REAL accuracy would zoom right back to 95% and I'd kill the enemy dead within a few shots.
Test 2: In VATS, with some rifles (not all) my REAL accuracy was about 40% to 50%. Rifles that I tested were the Hunting Rifle and the Gauss Rifle. However, many other rifles work just fine, such as the Varmint Rifle, Cowboy Repeater, Sniper Rifle and Plasma Rifle. (Of course the Gauss Rifle had been my intended endgame rifle so this was a huge bug for me.)
Additional notes: There are times where, because of clipping issues, my REAL accuracy with any weapon is 0% when my VATS accuracy says 95%; however, these are conditions that happen once in a while, for example when an enemy gets stuck in terrain. This special situation is rare, and is entirely different than the bug I'm talking about that affected me regardless of conditions.
This VATS accuracy bug happened consistently for particular weapons, regardless of the range or line of sight conditions.
Peace,
Drake