Air Arms S300 Bullpup Build

I had just enough 120 year old black walnut left over from my last Maurader bullpup stock to make another bullpup stock… this end of the slab had a few knots and sap wood with the odd wood worm hole so it didnt leave me a lot of clear timber for another “pretty” stock but ill work with what I have..

I managed to pick up a beautiful mint condition Air Arms S300 in .22 FAC for less than a hand full of magic beans the other day.. ;D

I have drawn up a simple thumb hole type stock for it like the one on this Ukrainian made BM-Raptor stock with minimal work involved to shape it.

Because the left over walnut is not pretty enough to polish I will give it a special suede textured paint finish that leaves the timber durable and looking like a synthetic stock. there is far less prep work needed for this finish but it can look very good if done right..

Let the sawdust begin…
I have started both walnut stocks by cutting the two square sides and trimming off any excess that is not needed for the router to follow etc.
As you can see the S300 stock has some knarly looking knots and voids with the odd wood worm hole for a bit of character too.. This timber is still too good to waist and it is very hardy and stable so it will still make a great stock, perfectly suited to be painted. I will dig out any unstable timber and fill with a filler when the time comes. [/color][/size]

From the bench saw to the router, this arvo I have made a good start on the S300 stock..
Unlike the all the “measure 5 times and cut once” on my pretty polished walnut Marauder stock, this one was very quick to cut out.. in total I have spent about 45 mins on it.
With the pretence that this stock will be painted I have really just cut loose with the plunge router bit and cut the whole stock out without any jigs/guides etc. I simply clamped it to my work bench and cut it out buy hand. I started by setting the 12mm plunge router to the depth of 20mm and cut about 2mm away from the lines then trimmed back to the lines. Once I was happy with the shape I set the router to the full 50mm depth and cut right through using the shank of the router bit as a following guide.

Normally Id attack the stocks in-letting first but because of the shape of this stock the in-letting was just as easy to do after cutting it out.
The first cut I made was a 16mm square relief groove for the trigger linkage and another cut just a little deeper at the rear for the trigger to recess into.

The air cylinder on the S300 is 1-1/4″ OD but unfortunately my wood working tool collection isn’t as extensive as my engineering tool collection so I don’t have a 1-1/4″ router bit suitable to cut the inlet so I used a 20mm one and ran 5 staggered depth cuts..

The result was very acceptable and only very slight ribs were left which I took care of with some sand paper wrapped around a short section of 1-1/4″ alloy tube.

Fits like a glove… next up some serious dust making shaping antics..

I cant get too carried away with the shaping of the stock until I make the forward scope mounts and router their recesses in the in-letting as I need square edges for the router guide to follow.
However I spent half an hour on shaping the rear and the pistol grip with the grinder fitted with an 80 grit sanding wheel… oh man that puppy sure makes some dust.. this is just a very quick initial shaping keeping well away from the final stock lines which will be followed by an orbital sander with various grades of paper and a drill mounted flapper wheel for the internal areas. The final lines will be refined by hand.

Its a little hard to see at this stage of the build but I have actually made this stock with a large target style offset for right handed shooting as opposed to my ambidextrous Marauder Bullpup stock. Even at this early stage it fits my hand very comfortably.

This build is really being done on a shoestring, it was not really an intentional project, the rifle was just to cheap to pass up and I had just enough scrap walnut to temp me into a stock for it.
For this reason I will attempt to build the whole project with the odds and ends laying around my workshop.
So far the only thing I have purchased for this build is sand paper and sanding disks. (About $10
worth) I already have most materials I need from other projects including the alloy and the stock paint so really the additional cost may only include screws, bolts and other hardware, (If I cant find any to suit in my box of tricks) a piece of picatinny rail, and the anodizing cost. 8)

The stock has been a very simple one to make as there is no technical routering or awkward fittings such as pressure gauges and safety catches to work around like the Marauder had.
There is a certain aspect of making the design up as I go without any drawings etc to complicate issues so something may jump out and bite me further down the track but lets hope all just falls into place.
I am yet to design or make the trigger and linkage but it will probably be much the same as the last one I made which has proven itself well. I will also be re-using the rubber recoil pad of the original stock which should fit the design of the stock nicely and give it a little more L.O.P which I feel this one needs..

After another hour on the stock and I have refined the lines and pre-fitted the original S300 recoil pad..
The pistol grip has been shortened about 12mm as it just looked too long and Ive cut the rear drop angle to meet the top of the recoil pad.
I’ve also mixed some 2 pot filler and filled all the imperfections so its almost done.

Still to do: to cut the in-letting recesses for the scope riser mounts and shape the fore grip forward of the pistol grip. Once this is done I will put a nice radius from the outside edges of the in-letting to the sides to get rid of that sharp edge.
For a rough and ready job I’m quite happy with this stock and very happy this second grade scrap walnut didn’t go to waste.

Its a little lighter and slimmer than my Marauder stock as the walnut slab lost a little fat through the thicknesser to square it all up before I started. The S300s air cylinder is the same size as the marauder so the scope risers will be similar and will be a little closer to the edge of the timber making them a bigger challenge to inlet.. I do however like the way this stock handles and balances, it has a “petite girl” feel to it and sits real nice when shouldered.

The scope riser mounts are roughed out and ready for finishing and drilling etc.. You may notice I made them a little different to the marauder mounts and added a extension off the bottom to mount the trigger bar on.
It was a pain in the ass to bolt the trigger mount on the last ones so I just cut these ones out of a much thicker (40mm) piece of aircraft grade 7075 alloy instead.. Im still designing as I go so unsure exactly how I’ll mount the trigger but it will be faster and easier than the last one you can be sure of that.
You may also notice that I have made the barrel clearance holes large enough for a new match 16mm OD Lothar Walther barrel to free float in 😉

I then marked out where they will sit aligning the forward mount with the stock securing bolt and trigger guard in mind.

Then I carefully cut the in-letting with a 4mm router bit and cut a slot for the trigger blade..

Once it was all sitting square and pretty I roughed out the fore end shape with the grinder mounted sanding disk..

and then tidied it up with the orbital sander..

Just the hole to mount the stock and trigger guard and a final sand and it will be ready to paint.

I have two triggers I have removed from a couple parted out Pcps so I will utilize them on my two bullpups to save a bit of time making some.

The pivot and linkage however I had to make so this is what I did.. a small wishbone extension attached with a cap screw to the front scope mount. I have milled down the top section of the trigger blade with a thinner tab to attach to the linkage rod.

The linkage rod was purchased from my local model shop which Im guessing they use for servo con rods etc. They are hard spring steel with a thread at one end and have many different screw on and solder on fittings to use with them.

I also spent a bit of time polishing the milling marks out of the scope risers

I had a bit of a rethink on the front connecting rod mounting flange, the pivot hole needs to be as close to the top pivot hole axis as possible to push the con rod in a direct “rearward” motion rather than in an upward ark at the same time as rearward.. this would make it hit the base of the scope risers and run out of travel..
So back in the mill it went and I moved the flange forward and trimmed of the extra material.

Then after a bit of final shaping and polishing I drilled and tapped it for the trigger blade. I added a piece of 1/4″ tube to space the blade a little lower to position it perfectly in the stock..

On to the rear trigger linkage.. I wanted to remove the trigger guard to get better access to the trigger blade but unfortunately the guard plays a big part in the triggers operation and adjustment..
there is a grub screw that retains a spring for engaging the trigger sear and to create adjustable trigger tension and also a roll pin through it that acts as a forward trigger stop..

To operate the rifle without the trigger guard required a new part to do both those jobs.. heres what I did..

After some careful measurements I made an alloy front block to work as the trigger stop and also to retain the spring.. I will drill and tap it for a grub screw to adjust tension too.

I made the rear trigger pivot connector basically the same as my Marauders one..

Once all bits were finished I assembled it all up and cut the conrod to length leaving enough length for adjustment on the rear thread on pivot clip. The front pivot clip was then soldered in place and I bent a slight goose neck in the con rod to clear the stock in-letting.

After a few adjustments to the rear trigger and conrod length I got it all working perfectly ;D

Ive made a trigger guard and drilled the stock mounting bolt hole into the base of the front scope riser mount and done the final sand on the stock ready to paint…

This shot of the underside shows just how slim this little pup is, it is much lighter than all my other bullpups and handles really well.

My blank Picatinny rail arrived which meant I could finally finish my metal work..
I ordered 3 of them of Ebay out of China, only $6 a piece and free postage!

The quality is as good as I hoped and they seem to be made from 6061 T6 alloy so they are nice and hard and great to machine.
I started by drilling and countersinking the holes at the correct spacing for the 4mm countersunk mounting cap screws (which came with the rails :))

Once done with the drilling I touched up the anodizing with some Aluminium blackening liquid..
This stuff works best when the alloy is heated slightly then applied with a small brush.. It is an etching acid that oxidises the alloy which is great for touch ups..

Once the alloy has turned black it needs to be washed off in cold water to kill the acid.
Here it is all touched up..

On to the riser mounts, with some careful marking up of the barrel centre I drilled and tapped the risers for the 4mm cap screws..

After trimming the rail to length I also decided to give the underside of the picatinny rail some shape to make it look like it belongs..

One thing I forgot to explain was the clamping system on this riser, on my Marauder bullpup I used the slitting saw to split the mount at the base and a cap screw through it from right to left to pinch it up on the air cylinder, on this one I went with an easier option of a 8mm grub screw in the base of each mount to nip up on the air cylinder.. works a charm.

Once every thing had its pretty Matt black coating done it was all assembled for the final time with a spot of moly paste on the trigger linkages..

Now its just the paint job on the stock and she’s all done! Custom bullpup number two 8)

I finally made the time to finish the stock, after a few light coats of the sandy textured primer and a good bake in the sun I have put three coats of matt black on it and it has now taken on the synthetic look..

Introducing my new .22 “AirArms S300-B”

Heres a vid of my last .25 cal Maurader build for those that havent seen it..
http://www.youtube.com/watch?v=lyiE4BeTEM0&feature=c4-overview&list=UU2IPmu-O9ahuxqdG1halidg