[Phonetics] Missile / Missle

[Cessna]

I was discussing with a friend of mine from class today, after learning about GA English.

This is how we would pronounce it in RP : /mI,saIɫ/
This is how they would pronounce it in GA: /mIs,ɫ/


What is the rule behind this, or rather in which category does it belong to, is it lexical distribution?

['mændtri] RP
['mænd,tri] GA


I think it has something with stress to do but I am not certain. Can anyone here help?