What, no BAR owners ???
The BAR is the better of the commercial semi-auto "hunting rifles". It dosen't have many of the foibles of the Remington's. The Winchester M100's were good rifles but cost of production and slow sales killed them off. That, and they only were in "short action", meaning the derivatives of the .308 cases.
The main "issue" with BAR's I saw in my game and fish career were those inflicting most firearms. Neglect and negligence in maintainance.
Your brother should learn how to properly field strip the gun and clean it routinely after range outings prior to storage. This will ensure longevity and reliability. Removing combustion deposits (carbon, mainly and unburned powder residue secondly, and thirdly primer compound residues.).
Most of the "stoppages" I saw with the Brownings were with guns that were abused. Shot, and then reloaded and set aside for extended periods. And then at the first shot when they failed to feed, the gun (or ammo) was blamed, not the idgit that failed to clean it....
Occasionly there was the gun that was shot with corroded or surplus corrosive ammo that caused problems, but these too, go in the neglect, neglignece category.
As regards magazines, the original are all that I'm aware of. These are excellent field rifles, but not "pseudo tactical" rifles. Expect to pay $$ for extra magazines. Most owners only own one magazine, a few two...
There were a few of these guns built with the so called "Salt wood" stocks. Most will have been rusted up and faded from the scene by now.
I'm even aware of a couple of the .300winmag BAR's that were converted to .458winmag. The biggest problem with these conversions is that the butt stocks couldn't take the recoil and would crack in the wrist area.
Overall decent rifles, but a tad heavy. Biggest resistance to acceptance was they were/are pricey... ditto accessories and extra magazines. Typical Browning...