I haven't tried it with an NEF, but I had a Lone Eagle single shot pistol in .357 mag that I had rechambered to 357 Max.
Both designs " breech up " the same way.
I shot three different cartridges ( 38 spec., .357 mag, & 357 Max ) with very good results, in my rechambered pistol .
A fellow in Kentucky , Knopp was his name, did my rechambering, as I remember the cost was $45. This was about 12 - 14 years ago.
He did a great job. I never had any type of problem, extraction, ejection , etc. with all 3 cartridges working 100% perfect.
Hope this is some help to you ,
Ben