I own a BAR, a Winchester that was converted to 1918A2 specs at some point in time, IIRC the barrel is dated '52; all Winchester BAR's were made in 1918. I love to shoot it, one of my favorite MG's.
The thing to keep in mind about the BAR is by WWII, which was when it saw the most use, it was really obsolete. Yes, it was reliable gun, but it did not have a quick change barrel and was not belt fed. As a squad automatic weapon, it did not hold a candle to the MG42, for example. The later FN-D did have a quick change barrel, but it was still magazine fed. The gas system is also a chore to clean, not a huge issue now, but it certainly was in the era of corrosive ammo.
To an extent, the BAR is still in front line service. The basic action of the FN MAG-58 AKA the US M240, is really just a BAR action turned upside down. Whereas the the toggle action on a BAR cam upward, id goes to the bottom on the MAG-58. The MAG-58/M240 is considered one of the most reliable machine guns in the world, that is a fact, not an opinion. In a nutshell, the MAG/240 is nothing more than an upside down BAR action with a MG42 top cover and a MG42 trigger group. That is a very simplistic description, but that's really what it is.
It was cutting edge technology when introduced, but obsolete by WWII. That said, it is a classic US martial arm. A neat, neat, gun with, IMO, a perfect ROF on its "fast" setting. I need to get out and shoot my BAR, it has been too long.