Vintage BSA Scorpion Pistol_ Strip Down Guide.

Introduction: Vintage BSA Scorpion Pistol_ Strip Down Guide.

The BSA Scorpion is a monster of an airgun pistol; in the 70's and 80's it was the most powerful around.

You may consider this a niche Instructable.

I bought a secondhand one in a private sale online.

I had never seen one in real life but I was fascinated by what I had read; when it arrived I laughed out loud; it's massive.

The reviews praise it's power and accuracy. (for targets only, not for vermin control).

I could not find a pictorial strip down guide anywhere on the internet, so here is my own.

Any improvements corrections or tips are welcome.

The exploded diagram is from the Chamber air gun spares site.{ I have modified it a little).
They supply a good range of spares for vintage air guns.

Step 1: Tools.

You will need:


A small flat head screwdriver.

A Posidrive screwdriver.

A 3mm Allen key.

A slotted tube         ( using a bicycle seat-post; this will be explained in the guide  )

An improvised spring compressor     ( using a sash-clamp; this will be explained in the guide  )

A wooden dowel.

Parallel punches ( you could get away with it without them)




A breach seal ( if needed )

A buffer washer ( if needed )

A piston seal ( if needed )

Step 2: Removing the Grip.

Firstly unscrew the bolt holding on the safety catch and remove the catch.
There is catch on the heel of the grip

Very carefully push a small screwdriver into the opening.

Study the photos; the aim is not to lever open the catch but to release the little arm that holds the catch on.

Once removed you can see how unusually delicate this component is for such a hefty beast.
Inside you will see the head of an allen bolt. 

Undo this.

At the rear underside of the pistol is a silver posidrive screw; undo this.


Carefully pull the grip away. 

It is much lighter than I thought; not solid plastic.

Step 3: Remove the Sights.

The front sight is held on by a single screw;undo this and remove the sight.


The rear sights held on by a single screw and a small peg; undo the screw and remove the sight.

Step 4: Remove the Barrel Pivot.

The barrel is held on by a roll bar; called the barrel axix pin; this is simply a tube with a split along its length.

These bars have small plastic plugs over them; carefully remove by levering out with a small blade.

I placed the cylinder over a block of wood with a hole under the axis pin.

Using a parallel punch I gently tapped it through.

Step 5: Removing the Trigger Assembly and Barrel.

Remove the  two silver trigger plate screws on each side of the trigger assembly.


Gently pull it away from the cylinder being aware of the long sear which is under a small amount of tension.


The barrel and attached parts can now be separated from the trigger housing by sliding the cocking lever out of the trigger plate.


A quick inspection shows that the plastic on my trigger has a crack in it but I don't think that this affects performance.

Step 6: Making a Spring Compressor.

There are countless ways to do this ranging from using the jaws of a workmate, a car jack, sash clamp etc.

I used a sash clamp as it seems the easiest and safest.

Firstly though you have to make a tool to relieve the compression on the mainspring retainer. . . I'll call this ' the reliever.'

This is simply a tube that fits into the back of the cylinder and the prongs sit either side of the mainspring retainer (which essentially  is just a large pin) ; 
A tube with a roughly one inch diameter is what you want; I used an old seat-post from a bike; it took about 1 minute to make with 3 cuts on each side with a hacksaw.


As you can see in the photo, I laid the sash clamp down (with some wooden blocks to protect the cylinder jaws.) and held everything down with bungees.

I inserted the reliever into the cylinder as described and gently tightened the clamp, not much just enough to take the spring pressure of the retainer.

Step 7: Removing the Retainer.

OK, gently tighten the clamp to relieve the pressure on the retainer; just a tiny bit; then tap the retainer out with a parallel punch.

It came out very easily; I could have probably used  a wooden dowel.

Step 8: Removing the Mainspring.

With the retainer removed I began to undo the sash clamp.

It only took a couple of turns and it was fully de-compressed.

Pull out the spring and the spring guide.

Step 9: Removing the Mainspring.

I had to use a wooden dowel to remove the piston.
I had to shape it to do the job.

It was not bad at all.

The buffer washer and piston ring are in good condition.

( The buffer washer can disintegrate and if not replaced in time seize the piston making it very, very hard to remove. )

Step 10: Possibly Replacing the Buffer Washer.

The piston head is held on by a type of circlip.
It is hidden under a washer.

Remove this washer easily by carefully levering it up and then inverting the piston so that it falls away.

The split washer can then be seen.

The washer can be opened up with two small screwdrivers,

This is fiddly and as my buffer washer is in good condition I do not need to do this.

Step 11: Cleaning and Re-greasing.

Clean everything and replace any parts that you need to.

Put moly grease behind the piston ring, all over the buffer washer.

My  mainspring is showing signs of wear on the ends; I put grease on the ends ( There is a type of spring-tar that some people use on the whole spring to reduce the twang ; I am not using this.)

I put grease on the spring guide also.

Step 12: Re-assembly- Mainspring.

Push the piston back in with the dowel.

Replace the mainspring and spring guide.

It is the same set up as before, with the clamp and seat post.

I found that I had to make a slightly deeper cut in the reliever; this was because the spring gude's two parts were separating.

Ok tighten up the clamp to allow the retainer pin in.

This just slides in; no hammer necessary.

Release the clamp slowly.

Step 13: Plunger.

While I'm here I should check the barrel latch

Put the barrel in the sash clamp to isolate the roll bar.

Tap out the roll bar and inspect; everything. re-grease and re-assemble using the clamp.

Step 14: Re-assembly- Trigger.

I pulled the long sear down with some hairy string and secured it there with an ikea pencil.

I slid the cocking lever into position in between the trigger housing and put the whole assembly into place.

This is how it looked until through the assembly hole, with the long sear resting on the intermediate sear.

I replaced the grip and safety lever.

After cocking I needed to move the safety lever up and down once to re-sit everything.

It is now very smooth to cock.

Happy Plinking.


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    3 years ago

    This is a brilliant guide. Thank you. My cylinder was seized in the barrel. Soaking in WD40 didn't help. My 87 year old father in law then suggested freezing the assembly. We did and it can apart easily...


    Reply 2 years ago

    It's an excellent guide. My piston is seized in the cylinder. Thanks for the advice about freezing, I'll give it try.


    Question 2 years ago on Step 14

    I took apart section 5 as illustrated cleaned oil out. Put back together and a small ball bearing, size of a pin head dropped out from somewhere in the main body, now pistol won't cock. Anyone out there got any ideas?


    Reply 2 years ago


    It's been so long since I did this, so I won't be of much help.
    I don't remember such a ball bearing but here is a link to the manuals for the MK1 and MK2 ; you could browse those and try and look for its original location.

    Good Luck


    Reply 2 years ago

    Thanks got that l have studied the diagrammatic of the disassembled parts and too can't see either the tiny boll bearing or the tiny spring that fell out later. It seems that both these tiny items maybe fell out of an area around the trigger? Is there any one out there that could help, as without these 2components the pistol won't even cock.
    thanks for what you sent

    Mark Ui
    Mark Ui

    2 years ago

    Dear connoinsseurs of BSA Scorpion 4.5.
    I got back my (long unused) BSA from late 70's back from my relative and it had an issue, only one: the safety switch was unsecure. I took t to repair, and after a month (!) I got it back with apologies of delay...and I was told that also spring was repaired (which had no problem). Now, my friend says that the spring is re-selled and mine re-placed with a weak one, since the original springs are wanted ones. Could this be possible? From my reflections back then is was near .22 but now my Scorpion is a limp. Could this kind of fraud be feasible? Yours, Markku


    Reply 2 years ago

    Hi Markku,

    Well anything is possible but I have never heard of the new springs being weak.

    I don't know where you are based but the springs are reasonably inexpensive in the UK:


    I only have a small field of knowledge about these pistols but I suggest that you register on this site and I think that someone in the forum will be able to help you; they know everything :

    Good luck

    Mark Ui
    Mark Ui

    Reply 2 years ago

    Thank you very much for your advice!


    6 years ago

    Excellent guide, thanks! These are classic air pistols and in my experience are more powerful than the HW45, not to mention better looking. The first airgun I ever shot was a BSA Scorpion, I won that very airgun now and cherish it. Did you know that BSA Scorpions were used as props in the Bond film "Octopussy"? :)


    7 years ago on Step 14

    Hi, thats one prob sorted for me but, I wonder if you can help with my air rifle its a haenel mod v it was my grand fathers but there is nothing in side, spring ,piston etc can you tell me where I can get parts or will other gun parts fit,

    Regards John

    i have a question , i wanted to rebuild my bsa scorpion , i change the piston for the new stainless one , and when i finalised the reassemble , they not cock .

    So i probably make a mistake somewhere , when i install barrel's cocking system the piston and spring are like on your's step 5 second picture , piston is compressed in and i take the hinge or rod of the barrel and install it in the most forward possition as possible , and after that i install the trigger assemble . but nothing he not cock . do you have and ideal of what can wrong . thanks you


    8 years ago on Introduction

    Thank you very much for this usefull guide .
    I have a similar pistol , cal 22 and I can't refile the air stroke as it gets stuck after first step . Please advise how can I fix this.
    Thanks alot for your time.


    Reply 8 years ago on Introduction

    Dear Mahmoudemad,

    I don't know how I missed it but I have only just just seen your question.

    I'm not sure that I understand it; I am not familiar with the term: refile the air stroke.

    If you mean that you cannot cock the pistol, then that may be due to the Buffer having disintegrated which causes the piston to seize. It has to be taken out, as far as I am aware, with brute force but by using softer than steel tools, eg that are made of wood, plastic or possibly copper.

    If you tell me more I may be able to help but my airgun  knowledge is quite limited.

    A site where you will get a comprehensive answer is ;
    They have a section for general airgun inquiries as well as one for vintage airguns.

    Good luck.