When did you purchase the lower? Pre or post FSA in 2013?
Posssibly legal. If it uses a proprietary bolt it may be legal. MSP LD has said that rifle must be cosmetically similar and 100% parts interchangeable to be banned. So if the bolt/BCG won't fit in a standard AR-15 it should be MD legal even with a non HBAR barrel.
As far as I am aware an AR in 6.5 Grendel is fine as non-HBAR. The cartridge is NOT useable in an AR-15. Bolt, magazine and barrel are different.