There's a modification available to use the 20-round magazine of the BAR, one possibility designer John Garand considered, or with a 7.62mm NATO barrel fitted, to use the magazine of the M14.
But the 8-round Garand clip is superior; and $50.00 or so will buy you a hundred of them, enough for 800 rounds of ammo. At $40-$50 each, that much ammunition in M14 magazines becomes a financial liability.
It takes a little practice to get used to the Garand's top-loading clip, which admittedly does prove a difficulty if a telescopic sight is to be fitted to the rifle. But A good hand with a Garand can easily outshoot a rookie using 20-round magazines, and likely scores more hits as well.
The old Garand is still hard to beat. But IMHO, stick with the 8-round clips that make such a neat package for carrying.
-archy-/-