Contact the NMLRA by phone. If you aren't a member, Join! Then ask them to send you a copy of their Match rules book, which defines what a Slug Gun is for their matches. And, then ask them to refer you to one of the slug gun shooters who might answer your questions.
What I know about slug guns I learned by going to Friendship and watching the slug gun shooters shoot their guns, then asking them questions about their guns when they were done and cleaning them. Much later, I learned that a friend of mine, George Mitchell, who I first met when he and his wife were shooting Hand made Kentucky Rifles at a club range, was a slug gun shooters, and he agreed to talk to another gun club about the guns. He owned 5 slug guns at the time, 2 original 1840s vintage pieces that required some repairs when he got them, 2 new guns made in the same styles and calibers as the older ones, and a huge, .69 Caliber Slug gun he made himself.
All his guns were loaded with false muzzles, and shot conical bullets. In fact, if there were any slugs guns at friendship shooting PRB, I don't recall seeing them. That may be the most distinct difference between slug guns and what we normally consider " traditional " rifles. Each of the false muzzles were designed and functioned slightly differently, but with the same purpose. Each centered the bullet in the false muzzle before it entered the barrel, and each was designed to wrap strips of light-oiled paper around the bullets to act as a seal between the lead bullet and the grooves of the rifling. Because the guns were firing bullets, only, they rifling is much more shallow cut and the Rate of Twist is much faster than is used in Traditional Barrels to shoot PRB.
Most of the Slug Guns you see today are Underhammer actions, but you can still find side-actions, including flint, percussion, and mule ear. The side action guns are usually reserved for shooting the shorter distance matches- out to 200 yds. For the longer matches, Scopes are allowed, and used, and that is where you see a majority of the guns having an underhammer action. That allows the scope to be set closer to the barrel, which makes canting a lesser problem. The big guns, with the scopes use " Cant Bars" - short bars that are fixed to the front of the barrel at 90 degree angles, and fit a special rest made to hold that gun on a custom made bench rest, to eliminate "canting". Bubble levels are often located near the muzzles to use to check the gun for level each time its places in its rest.
These are the kinds of things you see in Slug Guns, that you rarely, if ever, see in any traditional rifle. I hope this helps you understand what is involved in designing, and shooting a slug gun.
I consider the Slug Gun shooters to be the Research and Development group for all Black Powder shooters. Their ONLY goal is accuracy, and they will try anything that might give them smaller groups at obscene distances. :wink:
Much of what we know about loading, cleaning, and shooting MLers accurately can be credited to these men and women. They are wonderful people to be around. They always help each other, and strangers, and give information freely. They understand better than most, that its not the equipment that wins matches( altho it surely helps!) but the person pulling the trigger that matters in match shooting. Only the shooter can read the winds and make the decision when to squeeze that trigger. Only the shooter can aim the gun. And only the shooter picks his components, and loads the gun.
I took my friend, Frank Wright to Friendship one year, and we ran into George there. George was kind enough to show Frank his big gun, and the 2-piece bullets he made to shoot in it. He answered all of Frank's questions. When Frank was with the FBI, he was stationed for a few years at Quantico, and often served as a Range officer for the local civilian and marine shooters shooting MLing matches. He was familiar with Traditional rifles as we know them. He was familiar with Marine Snipers and their guns. But, he had not seen slug guns before that trip to Friendship. One question he asked George that he still remembers and talks about is what the tolerance George used in those heavy bullets. George said that most of the slug gun shooters will have a plus or minus tolerance of 1 grain, or even 1/2 grain in weight. He had the time, since he was retired, to weigh all his slugs, so there was ZERO variation in weight for his match slugs. Frank was in Shock hearing that. :shocked2: Oh, George had each bullet wrapped in paper towels, sitting in a wooden box, 10 bullets to the box, in individual grooves chiseled and routed into the wood. He used a couple of huge rubber bands to keep the boxes closed, which I found a bit unusual considering how much care he took otherwise with his bullets.
Oh, the other things you see more on the slug gun line, than elsewhere is that every shooter has at least 2 range rods( and sometimes 3!) leaning next to his loading station. One will have a cleaning jag on it. Another will have a loading jag on it. And sometimes a third is there with a bronze bore brush on it. These shooters are fanatics about cleaning their barrels between shots. :hatsoff:
George told Frank there are less than 200 slug gun shooters across the USA, and that after a couple of years of shooting, you meet most of them. Because almost all the guns are custom built, the group helps other shooters acquire parts, make barrels, false muzzles, etc. Its not done for free, but at least you have a source of skilled " help". These are very specialized guns, with special people building them, and shooting them.