The plan sounded solid, and everyone was ready for that. Your vehicles rides up as closest as you're willing to risk it while ensuring that it'll be close enough for the Gauss to hit with little difficulty, which brings to about 400 yards. With the scope that comes with the Gauss, that should be an easy enough shot.
Your Cars parked, it's manned .50 cals turn towards the hulking monster that seems to have noticed you..
The door popped, Gauss raised and aimed, then with a gentle squeeze on the trigger, the Gauss's Spike launched with a kick. It's deafening crack weren't so much of the actual shooting itself and more of the several sound barriers being broken immediately the moment it leaves the barrel, kicking back shock waves that blew away dusts not unlike when a tank fires it's main cannon. The gun's internal recoil dampeners are the only thing keeping your shoulder still attached to your body, even though you're definitely going to feel that tomorrow.
At the speed the Spike was travelling, 400 yards was less than a blink of an eye, the tip enters one of the Monster's arm, going through it's armor like hot knife through butter, a fraction of a second later, it came out the other side and kept going... another fraction of a heartbeat later, the entry point collapses from the sheer force that followed, crunching metal, flesh and bone, the shock continued until it hits the back end and for the smallest of moments, the back armor bulged..
Then the exit wound explodes outwards in a shower of metal, gore and bits of shattered bones, leaving that arm still barely attached to the body with what mangled flesh there was.
The spike that kept going hits one of the bunkers that just minding it's own business doing nothing and a piece of it explodes outwards as well from the force, you think that maybe the Stake's still going...
The Hulking Behemoth roared out a deafening roar of furious rage and blinding pain before it grabs the parked truck with it's three remaining arms, lifting it up with no difficulty at all and throw it towards your vehicles!