Hi,
That weight difference works out to be about 5%, which is probably within the range of alloy differences (in this case, as already noted, yours would be higher in antimony and/or tin than what the mould maker used when developing the mould.)
For recipes, if you have some for 170s, you should be ok. It's generally accepted that in cases like this with small variations in bullet weight you can load a lighter bullet with the next heavier bullet recipe, so your 180 data should work, too. In any case, don't go the other way: for example, DO NOT try to extrapolate 158 gr recipes. All this assumes, of course, reputable published data. Remember, start low, work up with ANY change in the recipe.
Rick C