Redwing, muzzle loading cartridge guns are fun. A lot of the old percussion muzzle loaders were turned at the muzzle for a bullet starter. A false muzzle isnt absolutely necessary. The bullet starter can be made to hold the bullet which should be just a hair over land diameter.
Some of the local long range muzzleloader shooters around here have been doing it thata way for a long time.
I've retrofit some Green Mountain barrels with false muzzle's. It takes a little doing to get the rifling to line up perfect. It can be done. I dont know if the alignment is all that important. The loose false muzzle on my Barry Darr barrel doesnt seem to hurt anything.
Here in the northwest we had an old timer named Ed Brown. He drilled and rifled his own barrels. He made them with a false muzzle. He wrote a book on how he did them. In his book he said he removed the false muzzle after the barrel was rifled, then he lapped the barrel so that it was just a little larger than the false muzzle. He said he did that so that it would have no chance of shaving lead when loading.
When Shutzen shooting started in Tacoma in the late nineteen
seventies Ed brown heard about it and headed to the range with one of his homemade outfits. Ed set his targets up at two hundred yards and blasted away. The local shooters told him it was a one hundred yard match. Ed told them he was used to shooting two hundred and would continue if it was ok. So, he did. He won the match. The last time I saw him was about fifteen years ago. He was shooting on the bench next to me. He got up to go to the restroom. On the way he clutched his chest, yelled for help and fell into the bramble bush's. Sue Miller did CPR on him till the medics showed up and took over. He lasted a couple more years, but that was the end of his shooting days. He was really old. I have his book in a box somewhere out in the shop. Man I'm a real windbag tonight!
You build a FMBL on a Martini, you'll have a ball shooting it.
Joe.