The forend is first shaped so that there's a widening of the forend starting 6" back from the muzzle. ..... this just exaggerates the swamp of the bbl {optional} . A rectangular piece of 1/8" thick brass has the partial octagon filed in and then the outside contour is filed when the front plate is fitted onto the bbl so that the contour is .03-.04 inside the forend shape. I use either .03 or .04 thick annealed brass for the Mcap body. The front plate fits into the Mcap body.
The end of the forend is sawed back so it's at least 3/16" behind the muzzle, filed smooth and the front plate is located on the bbl octagon and the outside contour is penciled on the end of the forend. This helps in shaping the forend for inletting the Mcap body which I form on a block that's got the forend contour.
The front plate is then hi temp silver soldered to the body from the inside, held together w/ baling wire...the solder line is nearly invisible. The closed end of the Mcap is then disk sanded to be perpendicular to the body and the open end likewise...I use calipers to ensure that the front and back end of the Mcap are parallel.
The wood for the Mcap inlet is roughed in according to the penciled outline and also a line is penciled in for the back of the Mcap. and then the Mcap is gradually fitted w/ more wood removal. Doesn't take that long although my instructions do......Fred