I have one on a PW and one on a Spolar. Both work very well and greatly reduce the effort required to load a lot of shells per hour. The machine requires adjustment now and then and when used in conjunction with an electric or hydrolic system can crush shells from time to time as things happen so quickly that if a shell is not aligned properly the loader will cycle and a shell gets crushed when coming off the feeder.
I strongly suggest that you drill out the head of the shell seat post on the feeder and put a small, strong ceramic magnet in the center. This will hold the shell centered and steady as the magnet grabs the steel primer. This slight modification works great. If you do not want to do it yourself email Whiz White at SW Supply or send him a PM on Trapshhoters and he will modify your post for about $20.00. .
They work OK with a manual machine. However, I tried one using an electric drive power system. and I could not make the hull feeder work. I adjusted everything, smoothed every part to a mirror finish, then played with the thing for months. I could not make it work consistently (like 20 shells without a foul up). I sold it, but still use the electric motor on my 800 plus.
I bought mine years ago and it came with a magnet. They are great. As far as bolting it up to a 800b it will work. When i first got mine they needed to know the serial number of the 800b. I think it wont work on the low number 800b units. If you call PW they will tell you.
One thing I've noticed with mine - if a stray piece of shot gets on the shell seat post it will force the shell to 'cock' and that is the typical cause of crushed hulls for me.
This week end I shall add the magnet to mine (GREAT idea) and at the same time notch the front of the rim around the shell seat post so as the shell moves forward the shot call be pushed out. Hadn't done it until now because I had no way to pin the shell in place, ...but the magnet...
I like the notch idea and will do that on mine because as you said it is a loose piece of shot that screws things up I got the magnets in a package of four or six at Home Depot and drilled out the post and used a two part epoxy to glue it in. Make sure it is flush or a little bit below the face of the shell ram and it should work well. It traps the shell with a noticable "click" and holds the shell solidly in place.
I had one on a PW loader and it took a little work to get it set up and aligned properly. I broke one of the feed tubes before I got it right so be careful. I had the hydraulic and the hull feeder. When it was all set up if was slick. It was a lot to watch however and I would not do it again. Either the Hydraulic or the hull feeder, but not both IMO.
I have used the two I used with a electric drive and the other with hydro drive and I have had nothing but good luck using them. Like I said, you need to get everything adjusted and aligned right. It does help to be somewhat mech. inclined. I find that most the people who don't like them or cant get them to work right are people who couldn't fix a garden hose. The two working together are art in motion and will cut your loading time in half.