I spoke with Brian from edgun west on this topic. He said the R5M chamber is not cut for slugs. He also let me know that the only slug he knew of that might fit was the H&N Grizzly. I tried them and can confirm that, with some extra effort they fit in my chamber. I can't speak to the accuracy of the Grizzlies yet, just that they fit my R5M. I tried some Nielson's in 34.7 HP-DB. I didn't feel like it was a good idea and didn't force it. It came up against a wall as soon as it touched the chamber. Much like I might expect after speaking with the dealer. That was a bit ago. I haven't had it more than a couple months I'd say. I know things are changing fast in the slug world, so I'm staying tuned for sure.