I'm bringing this one back up to the top. I bought the Caswell black oxide kit and wanted to post the results. IMO there is no reason to ever paint a bolt again....unless it was painted from the factory. The Caswell kit works perfectly. The only unknown at this point is how well the sealer works. If it does its job, the bolts will stay looking good for a long time.
NOTE...the black oxide kit is not the same thing as phosphating. That is the process that was used from the factory. I think it comes close to replicating that look though.
This picture shows the different stages that the fasteners I've done have gone through. The picture didn't turn out as good as I'd hoped but still shows the process. The different shades are easier to see in person. The first bolt is what I started with...the second is after bead blasting. The third picture is after a 30 second dip in the black oxide solution. The fourth pic is a 1 minute dip...the fifth pic is a 2 minute dip. Six pic is what the fasteners look like after coming out of the sealer. The last one is the finished product.
I've been giving averything a 2 minute dip. I let the fasteners sit for 4 days before handling them after the sealer was applied. The sealer takes a long time to dry. The sealer also darkens up the finish alot. After the initial four days, I wiped everything down with a shop rag. Some of the black will come off and you will be left with a dark gray finish. You can play with dip times to lighten or darken the final color.
Before/After sorry for the blurry picture