On the business end of the pictured 12 gauge shotgun is a ventilated medium pattern choke. Chokes are exchangeable and modify the spread of the load depending on what your planing on shooting. That choke has been on there for so long it might not come off.
For the record, I'm not a shooter or hunter I inherited some guns when my father passed on in 2000. One of these days I may see about selling all of them but one which has some family history supposedly. Apparently my great grandfather carried it when he served in the 1800's. But one never knows since my father was never known for telling the truth, the whole truth and nothing but the truth.
