Why fighters with BHG Core ID can't use 10 lvl. (Nomad cannons and Nomad Lasers) nomad guns I think, that Core scientists know about Nomad technologies not less than Order.
And, If I use this guns with special RP history that I will write I can use it on AP-18100 "Manta" for example?
The Core are fighting the Nomads in the Omicrons, and are at War with the Order to steal Nomad technology and control territory. They have a 90% core when using the 'open' Nomad Weapons (those sold on Evora shipyard). You can always get them ooRP to support whatever RP background you come up with (not that hard, since that is a main point of the Core).