So I was reading GP01 manuals(HG, MG, RG) and I came across the information that the Beam Gun function was only realized in the Full Burnern upgrade with the improved reactor.
As I understand:
-GP01: no Beam Gun function at all, even as Core Fighter II
-GP01Fb: Beam Gun function even as MS, the Beam Sabers can even swivel while stored.
Was this because it was the 1st time they tried to have the Beam Saber/Beam Gun combo in one weapon? Since we already had the RX-78-5 and successors with arm internal beam guns.