I'm kinda of two minds regarding this issue.
First, you might not kow it, nut the first Barrett .50 cal was built in a home shop, and was used for deer hunting in Virginia at ranges of up to a mile. The two guys who made it, built it to be used as a bench rifle, and placed on a hilltop with a wide view of the surrounding area. I don't have a clue why anybody at all would think it to be less accurate than a .308 caliber hunting rifle.
It did have a custom built receiver and barrel (also create in that home shop), because of course a lesser size would absolutely not work.
As to effect, a .50 cal should kill a Mack truck at a mile by penetrating the engine block... Understanding that principle tells us that body armor would be next to useless, and even power armor not much better. The effects on a human body are just not easily imaginable.
In the end, Bozar effects with a more normal appearing hunting rifle build would not be out of the question in RL, so I think that mods will be needed to get us to a good result for the .50, eh?