The B&T GHM9 is a semiautomatic 9mm pistol.
The GHM9 Gen 2 provides greater flexibility and modularity to the operator. The GHM9 Gen 2 accepts all APC9 PRO lower receivers, and allows the operator to change out barrels, handguards, and stocks.
The GHM9 BT-450002-2 utilizes the Sig Sauer P320 magazines.
The -G and -S look similar. A close up of the P320 lower is provided under the images tab. 320 can be seen marked on the left hand side of the lower.