The vent rib on the original Remington 600's and 600 Magnums (Magnums are rare as only 13,142 were built) was actually made of nylon and not steel. It was the same nylon material they used to produce the Remington Nylon 66 .22's.
The Remington 600's barrels were thin due to trying to save weight and it was said that Remington put the nylon ribs on them to make the barrel appear more robust.
Remington built the 600 mainly as a lightweight short barreled hunting rifle and they marketed it as a quick aiming, maneuverable, lightweight rifle with that short barrel. They marketed the vent rib as giving a better sight plane (as they are on shotguns) and reducing "mirage" from heat off the barrel.
So the nylon rib really did nothing for strengthening the barrel nor aiding in cooling in reality....and at the end of the day it just served to make the rifle look good. That is probably why the vent rib was not on the latter 600 Mohawk models brought out as the predecessor to the 600's in 1971.
There are some aftermarket ribs available for the Rem. 600's that are made of steel.
TAMU Wildlife and Fisheries Sciences
Boat racing is like a beautiful woman.......expensive, high maintenance, but well worth the fun!