I purchased a pair of the Emgo megaphone mufflers a few years ago, and they were packed with fiberglass-type packing around the long perforated tube that runs down the middle. There is also a perforated cross section within the long perforated tube. Contrary to what another member has indicated in this thread, I've never seen a Dunstall megaphone muffler that was straight through with no baffling. Maybe some of the shorty-style ones that came later on, but in the style similar to what Emgo is making, the mufflers I've seen have always had a perforated tube down the middle.
I run my 850 with Dunstall mufflers that have had the baffles sawed off, so they're just empty megaphones with the gattling gun style cap mounted on the end, and they are much louder than any pea-shooter style mufflers I've ever heard, and I think they sound a lot better. And when I say louder, I mean WAY louder. It's definitely not something to do unless you want your bike to be outside and well beyond what normal societal expectations are for what motorcycles are allowed to sound like. But it's a good loud, and for me it's the only way to go.
I've also run Nortons with unaltered Dunstalls, with the glass packing removed, and that provides a very throaty sound, and I think at least as loud as pea-shooters. And that's without having knocked out the perpendicular deflection disc that's in the middle of the long perforated tube. I've never run a set of them having done that.
And size does matter, too. The earliest Dunstalls were a smaller diameter than the mid-period type (like the one's Emgo makes now), and the exhaust tone was very much perceptibly higher. Beautiful in it's own right, but not as deep as the larger-bodied mid-period type -- which is what Emgo is similar to.
I once looked down one of the p-shooter mufflers that Kenny Dreer put on his bike, and they were just hollow with no baffling, no louvring, nothing. There's a member here selling one, and if you check his video you can get a sense of how gnarly an empty pea-shooter sounds. If you look in the for sale forum here, or on eBay, you can find the video link to the seller video for the Dreer bike that's currently for sale.
For stopping the head of the bolt from turning within the mounting bracket, I use a long thin screwdriver with a flat blade. When things start to get tight I just pulled it out and by that time the bolt was grabbing.
You should use ear protection when you're riding, too. I think the wind noise alone, from it whistling around through the helmet, is enough to damage your hearing.