If it were allowed and available I bet a huge amount of Texans would be buying 155mm just for bragging rights.
Alright, I'll bite, because I bet there's somebody out there that knows: why isn't it allowed? What rule by the ATF says that 150mm isn't an arm allowed by the second amendment?
It’s not administrative, but legislative.
ATF is empowered to interpret these laws. The law is quite clear that a howitzer is regulated.