What the barrel extension torque on the M4?
The TM does not have this value listed because the military doesn’t buy barrels and barrel extesnions separately. I am willing to bet there is no torque value if everything is lined up and assembled correctly.
On a “blueprinted” bolt gun I use 35 foot pounds to torque the barrel. Although I have done barrel extensions it has been many years and I cannot remember the torque spec I used.
If you stay somewhere between 35 and 50 foot pounds you should be fine. The index pin will prevent it from loosening.
(Yes I have read specs up to 200 foot pounds for bolt guns, but I have read more against than for this spec.)