SRML wire calculations

Has anyone had any experience with calculations for SRML wire.
I have searched through all the articles I can, googled it and even talked to several engineers. How do you figure the de-rate factor with more than one conductor in a raceway. Also this is an 392 c environment. I would appreciate any help in pointing me in the right direction.

A quick search found this
https://www.awcwire.com/productspec.aspx?id=srml

it looks like even the SRML wire dos not have a high enough rating
it looks like you should select MG wire 450 c
you will have to calculate the conduit fill

GaryS'
Thanks for the reply. I was looking for a chart for the de-rateing tables at that temperature the NEC does not give any information in article 310-15(16) I had read online in one of the many articles that the NEC does not cover this type wire and it has to me calculated outside, just do not know what the best way to do it would be.

With that high a temp rating I don't think you would need to de-rate for heat generation
but as the when wire temp goes up the resistance of the wire would also go up and would also cause a higher voltage drop for the wire I don't know if that's important to you or not
from your post you need a higher temp rating then 250c you should consider the MG wire 450c rating

Ok thanks I will do that, I have told my manger we would be better off with a contractor on this project instead of doing it in house.