I was having a hard time with the Falcon I just picked up. Its used and didn't have a weight in the butt. The weight bolts are essentially just set screws that you can buy at any hardware store. So I took my Falcon butt in, tried a few bolts just to see what would fit, then ended up with a few set screws to try out.
Now there are different grade bolts which will weigh differently. Example, an aluminium bolt won't weigh the same as a stainless steel. So I ended up with a half inch, inch and inch and a half figuring I could add them in to get a different weight. I ended up using all three and to be honest I don't have a scale to tell the weight of the cue nor the weight of the screws but its comfortable to me. A grade 8 steel set screw will be the heaviest tho. The guy at Ace said if I have issues with them slipping, I can add a dab of elmers glue to the tip of the screw to keep it from slipping.
If you are going the weight bolt route, this would work. If you are looking to add other weight, I'd be interested to hear what else is out there.