I've had a 28" 930 for a while. Recently, I've acquired the parts to turn it into a 930 SPX. What's the best way to get the sights adjusted? i.e. are there methods or shortcuts that can be used to avoid blasting through a bunch of slugs? Having mostly shot bird shot in the past, I only have 4 from a box of 5 rifled slugs. Normally, I'd just go to Walmart and pick up some more...but will they have any?