I tried out one of the Reima/Scott Slingshot jackets, the one with some pads built in. It was a sorry excuse for a jacket. The sleeves were so narrow they would bind up when you bent your arm, even with the pads removed they did not have room in them. It also had no room in the shoulders. If you raised your arms over your head the bottom of the jacket would be up at your nipples. I kept the fleece liner, and gave the shell to a homeless guy.
I'm wearing a Klim parka now, and have lots of arm room.
It is possible to dislocate your shoulder from a poorly fitting coat combine with a tight belt, like your backpack.
I learned this last winter with a coldpro POS jacket, and a tight toolbelt over it. It applies leverage on your arm and works to pry it down and out of your shoulder. I slipped on ice and caught myself on the way down, and ended up with a dislocation.
