If you build one it won't be the first. Perhaps the second, since I did this almost 20 years ago.
The barrel was a shallow groove .45 cal , and made for paper patch bullets. I made a false muzzle for it to allow easy and aligned seating of the 535 gr PP bullets .
I shot this rifle extensively in the 1000 yard matches in Ottawa as a member of the DCRA.
Basic rules were 2 sighters on target which you could convert if you wanted to, with 10 shots for score. The elevation drop after 30 shots or so was enough to drop you from a 4 to a 3 , but elevation loss was not the only problem since accuracy in general was impaired. I found that it was best to change the touch hole liner after every 1000 yard target shot, or after 2 targets if shooting at lesser ranges. Berylium copper liners seemed to last better than stainless steel. Part of the general accuracy loss was I believe partly due to the variable of the ignition system itself as the touch hole size changed. Don't forget a good flash shield to protect the shooter on the line beside you.