So what did I do. . .
First off pics of the muzzles. Pretty darn poor.
I took off all the finecast at the front of the bolter and sanded it flush before drilling out a 2mm hole. (pic below is the 1mm pilot hole)
Cut into small sections
Inserted into the drilled out bolter and cut to the same length. Tidyed up with a sanding sponge.
Muzzles drilled out. Job done