6 KG is a bit heavy for a pistol
Hold 6 KG at arm's length for any amount of time and your hands will start to shake. It's hard to be accurate when your hands are shaking. Now, put it in a rifle stock and you're talking. There are a lot of infantry weapons that weigh more than 6 KG. For example, the M-60 machine gun with bipod and a belt of 100 rounds probably weighs closer to 15 KG. A SAW (squad automatic weapon) weighs more than 6 KG. The old BAR weighed more than a SAW.