Highly recommend for building your ar - Geissele AR-15/M4 Reaction Rod

I can't say enough good things about this tool.
1) This is for the AR-15 mil spec. As long as your bolt has a standard AR-15 outer diameter and lug pattern this will work.
2) Used this to change the barrel out on my 6.5 Grendel. Grendel has the largest case head diameter that will fit in the AR-15 platform.
a) There is a manufacturer that builds an intermediate sized "AR-15". That rifle is not "Mil Spec". Research YOUR RIFLE to determine what you
need.
3) I don't know if it will work on a side charging upper, I had to remove the charging handle for it to fit in my standard upper.
4) After changing the barrel and getting the muzzle brake installed, this allowed me to keep the upper receiver level for scope installation.
5) It's not cheap, you do get what you pay for.