Thursday, 31 October 2013

Making a Custom Stock for the SMK B45-3

This is my first attempt at making a custom stock for an air rifle, but it would show me how easy or hard the process is. With this in mind i decided not to use a whole blank of quality wood, and use instead a plank of beech which could be made in two halves then glued together.

Lots of loud Ian Dury to work along to

Instead of a CAD design drawing that i don't have the first idea about, i sketched some designs in a note pad that i liked then using the existing stock drew an outline on a piece of brown heavy duty packing paper. I used a mix of Air Arms and Daystate PCP air rifles stock designs i quite liked as my insperation, doodling into a sketch book along with other projects till i was happy with it.  Now i could intergrate and extend the pump arm and move the barrel and compression tube support band forward, by bringing a length of wood out from the main stock that the pump arm would fit around.

God alone only knows what bit i was cutting here.

Once the design was down on wood it was time to cut the shapes out with a jigsaw, as i was having a high comb i needed to add some wood to the bottom of the butt stock.

Bits of wood stuck on to make the stock.

The stock was glued together and secured with 6 mm dowel for extra strength, the pump arm stayed in two halves as it had to be built around the rest and fitted neatly to the pump lever connecting pins.

All glued before the holes were drilled for the support dowel.

With the glued together blank in a vice supported with wood either side, i marked out and using a chisel slowly removed the wood for the action and trigger to fit into.

Very carefully chiseling out for the action to fit in.

 The wood at each side is to stop the stock from splitting when using the chisel, at first i didn't support the stock and lost a splinter of wood which had to be glued back on again.

Where the wood chipped off and glued back on.

I was pretty sloppy with my measurements and most of it was done by eye, but it seemed to work fine and i could always use filler to secure any loose fittings around the action. I tried many methods to remove excess wood, such as using a milling bit in a drill but it didn't prove effective enough.

The milling bit wasn't a great success.

However 40 grade sand disks just ripped through the wood with a lot more control for what i was looking for, then sanding by hand removed any ripples or flat surfaces.

This did the trick, and you can see where the white dowel was glued in as well.

I buy a lot of battery powered drills with the battery missing from carboot sales, then i just wire them up to one or two 12volt batteries depending on their voltage.

At a Quid a shot you can't go wrong.

After about four disks, some chiseling, and some rasping, i ended up with a shape i was happy with and a bucket full of sawdust, not to mention what ended up in my lungs and on my clothes.

Just some of the sawdust and chippings.

The next step was to chisel out the wood on the two halves of the pump arm, to fit around the compression tube and the bar from the stock.

Carefully removing wood so the pump arm will fit nice and snug to the bar that comes forward from the stock.

They need to be separate until i can line then up with the pin holes in the pump arm lever, and also so i could get them as flush as possible with the stock.

Yep, that fits nicely.

 Fits flush enough for a first attempt.

 This also involved a bit of sanding with the power drill, just so both sides fit snugly.

Evening off the other half.

The other little chiseling jobs was to fit the trigger guard off the old stock, this had to be done carefully as it had to line up to screw into the action at just the right place.

Removing wood for trigger guard.

But alas i think a little metal putty filler might be needed to sit the action in and for the trigger guard stock screw, or better still now i know where i went wrong maybe a brass collar would do the trick. I found a good use for some of the the saw dust, and that was too mixed it with glue and i could make a filler for any nicks or gaps in the wood.

Saw dust and wood glue filling small hole.

or where the wood didn't quite join and left a tiny gap.

Just see the once wide gap at the top of the picture.

But the odd tiny mishap aside i am quite chuffed with how it has come along so far, the fitting of the pins in the pump arm lever is some thing you got to get right first time if you want it to look good.

Looking good so far.

This is why i kept the pump arm in two parts so i could line up the holes in the lever on each half, and have the arm resting against the stock while the action was connected.

Two halves of pump arm ready to go

 The action was connected through the front screw in the trigger guard and the extension bar that holds the compression tube and barrel support, i used metal putty to sit the action in tight to the stock and hold the trigger return spring in the correct place (mostly).

Action fitting snugly despite the odd minor cock up.

I gouged out the rubber around the pin holes to release the pins on the pump arm which turned out to be a bit short,

The old tacky looking pump arm.

with the rubber pump arm removed i could carve the pump arm halves to fit.

More carving.

Old pins are a bit short

 It was at this point i decided to drill a third hole in the lever and holding one half of a arm against the lever i drilled where the pins would fit,

Another pin hole for a bit of extra strength.

Making sure pump arm fits the stock evenly.

 i repeated the proccess with the other half and made some new pins about three times as long to hold them in place.

Much longer pins than the originals.

With the pins in one half of the arm and through the lever i added metal putty around the lever and glued the other half of the arm once the pins had slipped into place,

Try to cover the holes for the pins.

i then clamped it till it set then secured it further with some six inch dowel and some super glue to set it solid.

Hole for the dowel.

Dowel glued in place before sawing and power sanding.

By using 60 grit paper on the disk sander i got the lines on the stock and pump arm to flow and line up, then it worked down through finer grades of sand paper till it felt smooth and was looking rather splendid.

Lots of sanding, Christ on a stick! there was lots of sanding.

I wanted a rubber butt plate so i decided to remove an inch from the rear of the stock, it would do fine for now until i found some rubber that looked the part. Also it is a doddle to pump up with the pump arm extended, and it now feels natural to hold it by the back of the pistol grip while doing this.

An inch needs to come of the butt.

With the stock sanded smooth as a babies bum i decided to apply some danish oil, in fact i must have applied about ten coats of the stuff because its looking just amazing and feels well silky to the touch.The wood looks a lot darker with a satin finish and you can really see some lovely grain.

Inch of wood removed and Danish oil applied.

This being my first ever attempt i must say i have surprised myself with how well it has turned out, i'll think i shall leave it as it is and not bother with any crosshatching or stippling. 

Lots more Danish oil applied.

I think i got an old Relum Telly i could try that with, i could even have a go at doing a target stock with that one.

Some easy leverage there.

Though all said and done i have learned a lot on this little excercise, next time using a complete blank would be a good start and actually measuring correctly instead of sizing things by eye. But i got to say it looks good and feels good as well, i'm going to enjoy using this not so little multi pump.

Not too bad, if i say so myself.


Fondest regards, Wing Commander Sir Nigel Tetlington-Smythe.

Thursday, 24 October 2013

Adjusting the Pump Stroke on the SMK B 45-3

In dire need of a decent stock, and a decent trigger wouldn't go amiss either.

Ideally on a multi-pump air rifle you want the pump head seal to be touching the valve at the end of the stroke, so you know all the air you are pumping is going where you want it. This means lass pumps to get the desired air pressure in the valve, usually there is adjustment on the pump rod to achieve this.

With the SMK B45-3 there is a pin that stops the pump head from rotating and therefore unable to adjust, but on a previous strip down i removed the pin and adjusted it up then locked it with the locking nut.

Hole where retaining pin went.

 But i didn't adjust it enough as there is still compressed air between the pump head seal and the valve, and this is evident when the air forces the arm back when you go to take the forth or fifth pump. So time to take the pump assembly out and tweak it till the valve gets the full stroke of the pump.

First step was to remove the screw that holds the pin the pump arm pivots on,

Securing screw for pump arm pin.

the with the pump arm loosened off the pin came out of it's holes and housing releasing the pump arm.

Pump arm pin.

The two small flat head screws at the front release the housing that supports the arm, and also supports the end of the barrel.

One of two tiny screws.

This now slips out.

Housing for pump arm and barrel.

With the housing removed the pump head assembly can now slide out, but being careful not to mark the pump head seal.

Out slides the pump assembly.

Pump head assembly with locking nut.

Now i've already remove the retaining pin previously it's just a matter of loosening the locking nut, now you can adjust the pump head assembl and tighten the locking nut again. However don't adjust it to much as the pump arm won't close fully.

Ooops, to much adjustment.

So then it's just a matter of taking it out again and adjusting it till it just touches the valve face, which after a couple of attempts i got it spot on.

parachute seal

Short of the air that gets trapped in the parachute seal there was no compressed air to push the pump arm back once it was back together. Hopefully i will only need five or six pumps to get the same muzzle velocity i was previously getting with eight pumps, oooh, the suspence is killing me. I can't wait.


Wing Commander Sir Nigel Tetlington-Smythe

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.