Are u trying to remove sr15 flash hider? I don't have the barrel extension. But The way I do is using the impact wrench and aac 3 prong adapter then plug it in and 3 seconds it will come off.
I know that KAC has proprietary tools. But the geissele reaction rod fits perfect. No damage was done.
I would suggest buying the geissele reaction rod and trying it. Can always be returned. But it’s the solution to the forever unfound KAC rod that hasn’t been in stock for years.
You will damage any extension regardless of whether or not you have the proper tool with the amount of rocksett and torque KAC is attaching muzzle devices with these days.
The Midwest industries version is actually much better than the Geissele (I have both for both 5.56 and .308). The MI version has a top "sail" that fits into the Charging handle channel that keeps everything that much more secure when doing things like tightening a barrel nut.