Robert Harper sent The Firearm Blog photos of a convertible FAL with a 5.56mm magazine adaptor and a user-removable barrel. Included in the images are different length gas pistons and springs, presumably for the different length barrel and handguard assemblies. One of the barrels is marked “.50 BEO”. It reportedly shoots 5.56mm, 7.62mm, and .50 Beowulf.
The Firearm Blog received no additional information on the rifle.
Thanks to Robert for the tip.