I'm pretty sure that your statement that Maryland law prohibits FTF transfers in Maryland is not correct...
I don't disagree, as already posted. Still doesn't matter. The OP is a MD resident. His father is a TX resident. If his father owns the long gun, then a FTF transaction in is illegal in any state per federal law, unless the OP has his C&R FFL and since the long gun in question qualifies as C&R.