This is the first major encounter you'll come across in Fallout 4 and killing the deathclaw at the Museum of Freedom without the Vertibird's minigun is a challenge. The most common reason that players end up fighting without the minigun at their disposal is that they simply run out of ammo. If this is the case, you'll have to rely on the weapons at your disposal, any explosives you may have in your inventory, and V.A.T.S. to target vital parts of the deathclaw's body to slow it down. Don't forget to utilize your environment - shooting at the abandoned cars in the streets of Concord and causing them to explode can take a significant chunk out of the deathclaw's health.