I would not at all bother with a sight. Generally paint doesn't fly accurately enough for such to be really effective. The consensus is to use a reference point along the back of your marker, over the top, or off the tip of the barrel as you have it pointed, see where the paint flys, and adjust from there with more shots as a followup. Barrel and perhaps a regulator will be the two biggest helps for accuracy that you could get right now. The rest is of little consequence.