Thursday, 24 October 2013

Adjusting Down the Power on the .177 Air Arms Shamal

They don't build them like this any more, or if they do it costs a mint.

Now i have a chronoscope i have been checking all my air rifles for power output, i also found it useful for diagnosing and confirming problems
i thought i might of had. When it came to putting the Air Arms Shamal through it's paces i was very pleased with it's shot to shot velocity with very little FPS variation, and filling up to 185 bar started me at the best place in the power curve. The only thing that had me concerned was H&N field trophies would produce 11.9 ft/lb, therefor a heavier pellet could put me over the UK legal limit of 12 ft/lb.

Air Arms Shamal, the most accurate rifle i have come across to date.

When the Shamal was first introduced in 1989 it came with ability to adjust the tension on the hammer spring slightly, allowing your pellet of choice to perform just below the legal limit. However that wouldn't wash nowadays as the police will test your rifle with a variety of pellets, so i thought better play it safe and tune the Shamal down a tad. What follows is what i did to achieve this, if you own a Shamal use this information wisely.

The stock comes away from the gun by removing three screws with different heads, this has to be removed to get access to the adjustment port at the rear of the hammer spring. At the front is a hex head screw that connects to the support band, this also is used to attach slings and bipods. 

Front stud for sling and bipod.

 Further up is a flat head screw, this one connects to in front of the trigger below the action. It's best to use the widest head you can that fills the whole channel, ill fitting screwdrivers can damage the screwhead. You can get proper gunsmith screwdrivers but they cost a bomb, any decent multi head screwdriver set should have one wide enough. They have the advantage of having the blade head the same length as the diameter of the shaft, full contact with the head is a bonus in any situation.

Main bearing center flat head screw.

Next is a hex head screw which is accessed through a hole at the front of the trigger guard, this screw also connects the stock to the gun itself.

Tricky little hex screw through trigger guard and stock

Finally in order to remove the stock the whole trigger guard needs to be removed, there is a smaller star head screw at the rear of the trigger guard that secures it to the stock. 

Final star screw to remove trigger guard.

Unfortunately i did not have a star head of the right size but was able to use a hex head instead, though i wouldn't suggest using this method repeatedly and i don't intend to.

Trigger guard removed.

And gently lift the action out.

Now the gun will simply lift out of the stock giving full access to the plastic dust cover in the adjustment port at the rear of the spring and hammer housing, which i was able to prize out with my thumb nail instead of something thin like feeler gauges.

Not easily noticable but there is the dust cover.

First i had to remove a locking grub screw that has a hex head before i could get to the adjustment screw, which is also adjusted with a hex head but a tad smaller.

locking grub screw between action and dust cover.

Looking face on to the rear of the gun, turning the screw anti-clockwise releases tension on the hammer spring and only needs small adjustments to make a difference. 

Best picture i could get of the adjustment screw deep inside.

 I first turned it a 180 degrees and put a H&N over the chronoscope, this was too much as the muzzle velocity was reading 10.9 ft/lb. 

Make sure you turn it anti clockwise to reduce the power.

Turning the screw clockwise 90 degrees gave me the reading i wanted of 11.4 ft/lb which is pretty much the at top of the power curve, i would imagine this would now perform under 12 ft/lb with heavier pellets. 

11.51 ft/lb, nice and legal.

But as i don't use them apart from Crosman Premier heavies in the SMK multi pump i couldn't really test them, besides the Premier Heavies are a hard pellet and give less muzzle energy than the H&N's when used in the Shamal. The SMK multi pump can chew pellets with thin skirts, so likes the more solidly constructed pellet.

Now the Shamal was performing with a more pleasant muzzle velocity i fitted and tightened the locking grub screw then popped in the dust cover, fitting the stock was a matter of reversing the instructions for removal.

The Air Arms Shamal is an incredibly accurate single shot PCP air rifle which i use for excellent results when hunting, it would be really good if used in FT or HFT as i can hit the Knockdown target at 45 yards when using the correct breathing technique. This is i have to admit , my favorite air rifle in my collection and you wouldn't be able to pry it from my cold dead fingers. It's quite heavy at over 10 lbs with scope and lamp fitted, but it's built to an excellent standard and i find it easy to shoot as i can lug it around using the sling the rest of the time. I can sleep easy now , knowing my favorite air rifle is safe and legal.


Wing Commander Sir Nigel Tetlington- Smythe. 

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