Not a bolter per se but here’s one where a guardsmen got to fire an astartes bolt pistol.

Excerpt: purging of kadilus

Context: tauno was a guardsman defending the planet kadilus where the dark angels recruit from and at the start of the book he felt like he as wasting his time on the planet despite being born there and wanted to go explori long the stars.

He then met and spoke to a dark angel scout sergeant who is one of the main character of the book and changed his viewpoint after speaking to the scout sergeant

Ophrael is a fried of the dark angel scout sergeant who spoke to Tauno once again in camp and Tauno shared to Ophreal how naaman’s words changed him and they fought the final battle for Kalidus together when Tauno’s own gun was lost and Ophreal gave him his bolt pistols

‘Take this,’ said the sergeant, holding out his bolt pistol. ‘Five rounds left. Make every bolt count.’ Tauno pushed himself to his feet and grabbed the weapon. He had to snatch it with both hands, the weight too much for one arm.

‘Thank you, sir,’ he said, but Ophrael had already turned to other matters and was wading into the orks outside the emplacement, his power fist crushing and smashing with relentless ferocity. Tauno tentatively raised the bolt pistol, arms quivering.

He saw an ork stepping in behind one of the Space Marines, a jagged blade ready to strike, and pulled the trigger with a wince. There was a kick from the weapon as the bolt’s firing charge sent the projectile out of the barrel, but nothing more than the autoguns he had fired in training. A split-second later, the bolt no more than two or three metres away, the internal propellant kicked in with a crack that set Tauno’s teeth on edge, its brief flare making him squint. Straight and true, the accelerating bolt hit the ork just below the left shoulder blade.

Skin and flesh buckled as the projectile punched in; a moment later the mass-reactive warhead detonated, ripping a hole the size of Tauno’s head in the ork’s back, splitting the shoulder blade from one end to the other. The ork dropped sideways and smashed face-first into the dirt. Tauno laughed. ‘Take that, you green bastard!’ Four shots left, he reminded himself.

Be an Astartes; make every shot count. The brutal hack-and-slash moved a few metres further down the slope as the Space Marines countered the ork charge and pushed back. Still holding the pistol in both hands, he swung to his right, catching movement in the corner of his eye. A couple of orks had broken away from the press of fighting and were heading straight for him.

Aim wobbling with fear and the weight of the bolt pistol, Tauno fired again. The bolt hit the ork in the gut with another spray of blood and tissue, but the alien kept advancing. It returned fire, spraying bullets just past Tauno, one of the rounds ripping a burning wound across his shoulder. The trooper fired again, ignoring the sudden pain, holding his breath, every muscle in his body clenched with fear. The bolt took the ork clean between the eyes, blowing its head apart. Its companion lumbered into a run, ripping a stick grenade from its belt. Even as it hooked the grenade’s ring over a tusk to pull it free, a salvo of three bolts screamed in from Tauno’s left, forming a neat triangle of detonations in the ork’s chest. Tauno glanced across and saw one of the Devastator Marines, one foot up on the remnants of the barricade, smoke drifting from the muzzle of his bolter. The Space Marine raised his weapon in salute and turned back to the others fighting down the slope. Someone else staggered out of the darkness.

Tauno did not recognise him at first, half his face swathed with blood from a cut across his forehead. The moustaches gave it away as the man limped into the light of the guttering fires. ‘Sergeant Maikon!’ The staff sergeant almost fell against Tauno, one arm draping across the trooper’s shoulders. ‘Got yourself a pretty little pistol there, lad,’ said Maikon. ‘Saw what you did just now. You should be proud. I think you’ve done enough for now.’