The ASVK wasn’t my usual choice of rifle. I tended to favour the Accuracy International L115. But this was a new thing the Russians had been “field testing” against revolutionaries in Syria, and one of our people had smuggled one out to us.

As I lugged it through the undergrowth towards the next checkpoint, I had to conclude that it was a bit of a beast. Even though the Russians had stripped back its parts to the absolute minimum it still weighed almost three times my regular choice of longarm with a full magazine. Its hefty flash suppressor, at the end of the barrel, though, gave it a decent balance, even though it also conferred a... distinctive silhouette. My spotter, Rocker, had already nicknamed it "the cotton bud".

It was pretty close in both looks and design to the Barratt .50. The Yanks had designed that back in the 80s as an anti-materiel rifle,designed to punch through light armour and into things like engine blocks or driving compartments. But our Republican terrorist friends in Northern Ireland had made the Barratt infamous after they put one into the hands of their best sniper to use it as an anti-personnel weapon, punching clean through the steel/ceramic chest plates in the body armour of patrolling squaddies. It was before my time by a long way, but guys who remembered - who'd been there - had talked about the fear the weapon had created amongst those deployed on the streets of Armagh and North Belfast, or out on isolated patrols along the border with the Republic of Ireland. Getting hit was basically the instant "off" switch. From alive, alert and professional to dead in less time than it took you to register the sonic boom.

Even car bombs hadn't created the same level of paranoia as that Barratt.

And now the Russians had improved on the same formula and someone had decided that muggins was the right choice to take it out on an extended field test across Salisbury Plain. The idea was to give it as much of a battering as we could in "realistic" conditions and, of course, I was expected to write a full report on the experience of working with the weapon. Hence five days of living rough, just me and Rocker. We saw Captain Starling at the checkpoints, twice a day, who gave us a grid reference for a target, a time by which we had to be there and an outline briefing on what to expect. It was noticeable that the distance to each checkpoint was getting longer each time and the likelihood of us getting to a reasonable range was getting smaller.

It was day five and we were looking foward to putting away the last target, calling it done and having a long, hot soak followed by a cold drink. Starling had met us an hour before and we had twenty minutes to reach a target three kilometres away. On a good day, well rested and on the track, I could probably run that comfortably. But with twenty kilos of kit, four days of bad sleep, grass clumps and mud underfoot and patience in short supply, we'd be lucky to make it half that in time to take up a decent firing position.

But that was Rocker's problem.

Spotters were there to put the sniper in the right place at the right time with the right information to take the right shot. It was his job to check the weather reports and read the terrain and study the satellite pictures that would tell him where and when the best shot was to be taken from for the target I was expected to shoot. I just had to turn up and not fuck it up.

Right now, we were heading with all speed towards a less-than-deal option. But given the time we had, there was little other choice, by Rocker's assessment, and I had to trust his judgement. The knoll ahead of us was over a kilometre from the target.

In principle, a good shot followed a good set-up. That meant having time to infiltrate a location without being seen, to locate and identfy the target, set up a firing position, check all parameters, take the shot and exfiltrate post-haste. But this was not going to be that.

'We're five minutes from confirm,' said Rocker as we moved as rapidly as we could to the point he had selected, still with no certainty that it was even going to be the right place for the shot. Five minutes until the kill order would be confirmed. That was basically our deadline to be ready to take the shot. We might make it, just.

We had no illusions. Whilst, on paper, this was a test of the ASVK, it was also a test of us and our performance. Starling was looking for our limits as much as he was the rifle's. If you can break the shooter, you can break the shot.

We skirted the hill, avoiding silhouetting ourselves on the top, and found the rocky outcrop Rocker had been hoping for. Without words, he dropped his pack, threw out the mat for me and pulled the camo netting out in one swift action. I was already on my stomach on the mat, checking the position as he pulled the net over our heads and joined me, his range finder at the ready.

'One minute to confirm,' he said, frantically searching for our target.

They put dummy targets out, too. Missing your window was bad. Missing your shot was worse. But putting a shot through the wrong target... Well, that just wasn't something you wanted to do, put it that way.

'Target located,' he reported, just as the radio crackled and we both heard Starling over our earpieces.

'X-Ray Three One, this is X-Ray Zero. Mission confirmed,' said Starling. 'Shot is a go. Confirm, over.'

Rocker was furiously cross-checking the grid reference against the target he could see, scribbling the details down for me to find it in my scope.

'X-Ray Three One, this is X-Ray Zero, confirm, over,' said Starling again. That was it. That was our last call to confirm,

'X-Ray Three One, confirm,' said Rocker, and tapped me on the arm - the signal to take the shot.

I had the target. It was a human replica made of gelatin and pig's blood, dressed in a generic uniform and with a full set of body armour and a helmet. I was, under most circumstances, a head-shot guy. It was more certain in most situations. But helmets were good at causing unpredictable deflections of even the heaviest of rounds, so I had my cross-hairs on the target's centre of mass. All that same, at this range, the target was barely the size of my little fingernail. I had done my best to account for wind and drop, but it was as much an art as a science. Rocker gave me the numbers, but it was my job to judge how the rifle would respond to the little tweaks.

To be fair to Starling, that was another reason why he had left this, the hardest shot, until last.

As Rocker tapped my arm, my finger compressed on the trigger in a single smooth follow-through, there was an almighty roar, a rushing sense of light and sound and, as I gently released the trigger, I was immediately aware of something quite wrong with the picture.