A couple of usability issues.
1. You use 0.33 as the minimum horizontal swipe to trigger navigation. I have small hands and swiping that far across in landscape orientation even on something as small as an iPhone is physically uncomfortable. Would suggest you set it to 0.10 or so. Ideally it'd be affected by acceleration like native controls, but that's probably at the point of diminishing returns.
2. I have been trained to expect some animation when switching images. Trying to match the swipe speed is again, likely not worth the effort but perhaps just animate quickly, say in 0.05 or 0.1s or so, to make the transition less jarring. CSS animations should make this pretty simple.