Regan Nonneman rechambered 2 Marlin 336s for me, a 336 SC from 30-30 to 307 and a 336 SD from 35 to 356. Both work fine. Nonneman told me that the Marlin 336 ERs that were factory made in 356 used regular production 336 receivers, no special heat treating or physical strengthening. The 336 ERs were spectacularly unsuccessful, so have become collectables and Winchester seldom runs loads of factory ammo in either 307 or 356, so they are virtual orphans if you don't reload. Exercising 20/20 hindsight, I wish that I hadn't had the work done, particularly to the 336 SD that I bought in as new in the box condition.
Both work fine with ammo loaded to published pressures using 308 brass.
