Ok, cool. I don't know much at all about the GT-14, but I'll surmise that it has a tube similar or the same as the PVS-14s do and simply in a commercial housing. You're probably good to go on 5.56, and personally I use my PVS-14 on Grendels also. Even my 10.5" has some heft to it with the 762-SD on it. You might be able to find out more info in the Arfcom NVG forum or some of the others.
I haven't used my tube on the Grendels very much, but I'm still ticking along with no apparent damage for now. A very light Grendel would start to make me nervous with stout loads. I usually leave mine head mounted and just use an IR laser though.
I haven't used my tube on the Grendels very much, but I'm still ticking along with no apparent damage for now. A very light Grendel would start to make me nervous with stout loads. I usually leave mine head mounted and just use an IR laser though.