The company that built them was Arms Tech, LTd. in Phoenix.
It was built for a very short government run, perhaps a dozen rifles total in military service.
Army units were using this modified BAR as an Interdiction Rifle, in .300 Winchester Magnum. It's heavily reworked, with a 10-round detachable magazine, McMillan one-piece stock, and heavy contour stainless steel barrel. They used the steel-receivered BAR, not the alloy lightweight variant. It's seen limited use in Bosnia and Serbia, spanning the gap between the .308 bolt guns, and the .50 caliber Brownings. Supposedly, it worked quite well as a counter-sniper rifle against the local snipers shooting from the apartments.
Arms Tech has always been tight-lipped about these rifles, and no longer builds them. I've approached them on several occasions to rebuild an older magnum BAR I bought for the conversion - no reply. Some of these rifles were made for commercial purchase, and show up in the blue book description:
SUPER MATCH INTERDICTION POLICE MODEL
- .243 Win., .300 Win. Mag., or .308 Win. (standard) cal., features 22 in. free floating Schnieder or Douglas air gauged stainless steel barrel, gas operation, McMillan stock, updated trigger group, detachable box mag., 13¼ lbs. Limited mfg. 1996-98.
Grading 100% 98% 95% 90% 80% 70% 60% 50% 40% 30% 20% 10%
$3,950 $3,650 $3,300 $3,000 $2,750 $2,350 $2,000
Last MSR was $4,800.