If it is a standard AR-15 lower! An AR-15 lower is an AR-15 Lower. It would be good to attach a picture so we see it. A standard AR-15 Lower is the same for all the following whether it has a 5.56/223, 6.8 SPC, 6.5 Grendel, 6. 450 Bushmaster,458 SOCOM, 300 Blackout, 204, or 762X39 Upper on it. The only thing that changes is the upper due to the barrel (Cal.) the bolt and or the magazine it requires in most cases. If you are going to the 6.8 on your lower there should be no problem at all.
The Constitution is not an instrument for the Government to restrain the people. It is an instrument for the people to restrain the Government!
“Americans have the right and advantage of being armed. Unlike the people of other countries, whose leaders are afraid to trust them with arms.”
James Madison. Author of the 2nd Amendment