Can't see how you could stand the smell of the 90wt gear oil. YUK.. As for high pressure additives, ATF has all the high pressure qualities your AR will ever need. After all, it seems to handle the shearing effects of gears and chains in both transmissions and transfer cases in 4X4's just fine and with Dexron VI it handles it for up to 100,000 miles... 90 wt gear oil not only smells like sht, it won't protect your rifle any better either. Especially in cold weather. Straight up synthetic ATF is better lube than any gun oil on the market all by itself.