I use a guillotine type cutter and cut a bunch of strips 1 inch wide but it relys on me keeping the edge of the roll flat with the top. Its a wide roll of paper and by the time the knife gets to the end the strip may be a bit wider or narrower.
I gather the strips , get them aligned and put a staple through one end then use the template to cut the angles.
I might experiment with ways like yours.
I turned up a copper slug today. Half is .397 and half .399. With the 397 in front it slides down the bore until the muzzle where the .399 hangs up. It can be pulled out with the fingers so its not much.
So Vic , you were right. Some GM barrels have a slight choke. Is this good or bad? I dont know but I might leave it there a bit longer. Its right at the muzzle so thats better that I thought.