i bet Ruger's new Precison Rifle is up there, but still, this is an impossible uestion. if you could barow down by price range/ caliber or something, it would help.
most likely it's going to be some model buil on a blueprinted 700 action, i consider those "mass-produced". but then again, the Knight's Armament SASS are giving even bolts a run nowadays. it really depends on the cost's you are considering, and when the distances you are considering for most accurate. the MOST ACCURATE 100 yard rifle is going to be whole lot different than the MOST ACCURATE 1000 yard plus rifle, your talking 6mm benchrest calibers to .338 Lapua's etc. 6.5 Creedmoor is probably filling the "mass-production" and "affordable" most accurate distace cartridge at the moment.
Nosler's new 26 is going to be i there too, as the best for a certain distance.
if your asking for what to purchase, give us your distance reuirements and price range. i would like to get my hands on the ruger RMR personally if i was looking right now. but it depends on so many variables of what you want and if you want a semi/bolt or whatever.