I'm making a 12 ga adapter for my M203. Due to obvious length contraints, i.e. the 40mm barrel only opens up to about 4.9", the shotshell barrel length will be a little under 7" long. I'm wondering if I should have a choke installing in the barrel or just say fuck it and keep it cylinder bore. I'm only planning on shooting the Federal 1-7/8" buckshot and slugs.