Shin Sung Career 707 .22 Carbine PCP Air Rifle Lockdown maintenance

April 14, 2020 at 2:01 pm

Unable to go shooting due to the UK Government Covid-19 Lockdown rules, I continued my maintenance program with a stipdown of my Career 707 .22 PCP carbine. This rifle requires a Firearms Certificate, being rated at 28 ftlbs, and is the most powerful air rifle that I own and has given good service for 15 years, accounting for hundreds of rabbits in that time. All the seals were replaced, when I bought the rifle, the only one to fail being at the pressure gauge, which was easily accessed and replaced.

Firing H&N Baracuda Hunter Extreme 19 grain pellets it has proved itself in situations where a .22 rimfire rifle would be dangerous to use, such as public parks and gardens. Being extremely accurate, it has a safe rabbit killing range beyond 40 yards, allowing for pellet drop.

My first check was to see if the Career was still holding air. It had been ok in September, when I had shot a rabbit in my brother in law’s vegetable garden, only needing a top up from the diving bottle. This time the pressure gauge on the under side of the lower air cylinder was showing empty, ideal for safety when working on any precharged ¬†pneumatic weapon. Removing the magazine, I cocked and fired the rifle into the ground, there being only the sound the hammer striking the air valve and a weak puff of air from the muzzle.

A quick inspection of the rifle highlighted that three small screws were missing from the sight cover at the muzzle end of the barrel, being held on by the one remaining screw. This a classic example of regular use, taking the rifle out, only topping up the air, then putting it away again without checking it over. I have never needed to use the rifle over open sights anyway, it having an excellent Walther telescopic sight, which has a 3 x 9 magnification range through a 40 mm coated lens. The scope also benefits from an illuminated reticle for low light conditions and an adjustable paralax ideal for setting zero at extended ranges. A check of the illuminated reticule showed that a new battery was needed. I used the Career a lot in low light conditions after dusk in a public park and had forgotten to return the setting back to zero the last time that I had used it. Not for the first time I must add. A new CR2032 battery was fitted.

A recurring  problem that I had been living with, when using the Career, was the loosening of the butt section, due to the fixing nut unwinding due to the vibration on firing. During one evening session, when I shot about a dozen rabbits, the butt section had detached completely, forcing me to return home. It was obvious from my last tightening of the butt fixing nut, was that something had stripped. This was a prolem that I now intended to look at.

To undo the butt, the rubber bung at the rear has to be prised out with fine bladed screwdriver. To remove the fixing nut, which is deep inside the butt, a special tool is needed for this. I machined up a 20 mm diameter boss with two lugs, that locate in the fixing nut, which I attached to a length of 19 mm tubing. With a tommy bar at the other end, this works perfectly, but I am sure that the 19 mm tube with the lugs cut, or filed into end would work ok. I have a lathe and a small milling machine in my workshop, so it was just as easy to do a proper job.

With the nut and spring washer removed, the butt slides off the fixing tube. In my case the tube was only a tight finger fit, due to the end of the rifle end of the tube being partially stripped.

The start of the thread in the rifle was also worn, so chased down the worn thread on the fixing tube with an M15 x 1.0 mm pitch die, extending the thread by 6 mm, then turned off 6 mm of the worn thread, the above image before reducing the overall length. On reassembly I applied a spot of red Loctite to the end of the thread and tightened it back into the rifle with the tube gripped in a vice. It is now fixed solidly in place.

The next job was to check out the cocking and loading mechanism. First removing the two scope rail M4 csk srews, then the long M4 csk screw behind the rail. Using a hide mallet, the cover was tapped off upwards from the trigger end.

With the cover off, the full working of the mechanism is exposed, pivoting the under lever down pulls back the hammer and cocks the rifle. At the same time the lever in the above image draws back the pellet probe and the cam that controls the movement of the pellet feed block to the magazine.

The magazine is spring assisted, pushing the pellet forward into the hole exposed in the feed block, as it slides across from the firing position.

On the other side of the feed is the pellet stop, which has to be adjusted to suit the length of pellet used. The rifle was designed to be used with a 40 grain air bullet, now banned from sale in the UK, which took the maximum length setting. My original choice of pellet was the 21 grain Bisley Magnum pellet, which needed an adjustment for it’s shorter length, then going down to the shorter 19 grain H&N Baracuda Hunter Extreme, another adjustment was necessary. Once set, only that pellet can be used. I once had ¬† pellets in my pocket with an odd Bisley Magnum, being longer than the H&M, the Magnum stuck out of the feed block and was crushed, when the feed block was drawn back to the firing position, jamming the mechanism. Impossible to correct in the field, that was the end of my shooting session, needing to return home to strip and clear the mechanism of the crushed pellet.

This a top view of the cam plate pulled back in the feed position, the block has received the pellet from the spring loaded magazine and the rifle is cocked.

This the view from the other side, with the cam plate pushed for ward and the rifle ready to fire. The feed block has been drawn across by the cam into line with the barrel.

 

This is a view of the pellet probe and the feed block in position for firing with the cam plate removed.

With the feed block held in position by the cam, the final part of the loading operation pushes the pellet probe forward, through the feed block, then pushing the pellet ahead of the transfer port into the barrel.

The spring loaded hammer slides in a tube under the rigger mechanism, which is released, when the trigger is squeezed, speeding the hammer forward to make contact with the end of the air release valve, which in turn is pushed off its seat, releasing a measured blast of air, up through the transfer port behind the pellet, double O ring seals preventing loss of air back along the pellet probe, the pellet with nowhere to go, but down the barrel toward its target.

You will agree that it is an ingenious method for feeding pellets from a magazine, but it works every time.

After a generous spraying of the working parts with Bisley gun oil, the rifle was reassembled and the Walther telescopic sight refitted. An initial slow charging of the air cylinders from the diving bottle, produced a slight hiss of escaping air, but a quick turn of the bottle control valve, forced air in at pressure and the seals bedded down. All that was needed was to reset the sight zero at 30 yards on my garden range and the Career 707 was ready for use again, once the Lockdown is over.