I would respectfully suggest that Nonneman knows more about Marlin 336s than you or I will ever know. He told me that he Rockwell tests every action that he rechambers and that he has never, no never, found a soft Marlin action.
Where did you get the information that the heat treatment of the 336ER actions was different from any other 336 action? My contact at Marlin told me that that 336ER actions were no different than any other 336. Of course Marlin would say the conversion is unsafe, their liability attorneys wouldn't allow them to say anything else. Besides, anyone with half a brain knows that you void any warranty, written or implied, when you customize any commercial firearm.
I have had a couple of original 336ERs and currently have a couple of custom 336s in 356 that feed and fire without a hitch. As I recall, Nonneman does some milling to the lever, in addition to running a reamer to cut a new chamber. If you are familiar with the 336 extractor, you'll know that it is just a spring steel clip and is a universal fit for both rimmed and rimless cartridges, so no modification is necessary.
I think that I paid $185 for the 336CS that I had Nonneman rechamber from 35 to 356 and I can't see any reason to be unhappy, now or down the road. It's not like I'm ruinning the collector's value or anything. Heck, if I could find a nice 336A, 336SC, or 336SD in 35, I'd have Nonneman do another conversion for me.
Testimony from a statisfied customer!
Jeff
