BSA Light Pattern

[Chippendale]

Here is a short guide to dismantling a B.S.A underlever air rifle to inspect or replace the mainspring and piston head. It is the way I would do it.

All the main points are included but some people might tackle the task in a slightly different order. This is offered as a basic guide only and I recommend that you experiment and adopt the way that suits you best, but please remember to keep safety in mind at all times.

Before I start here are a few words of caution about tools.

When attempting to take one of these guns apart I would recommend the use of a gun maker’s turn screw, engineer’s drivers or other parallel bladed screwdriver. The gun screws on these guns have straight slots cut into their heads which are not suited to carpenter's/general screwdrivers which have a tapered blade.

If these unsuitable tools are used, damage can easily be done to the finish of the screw heads themselves which is difficult to remedy. Irreparable damage occurs because the tapered blade always wants to lever itself out of the slot when any pressure is applied to tighten the screw in question. If proper engineer's screwdrivers cannot be obtained, ordinary screwdrivers can be adapted by grinding the blade profile into a parallel blade.



How to dismantle a pre WW2 B.S.A Underlever Air rifle

Probably the main reason for dismantling the gun would be for regular service and in order to change the spring/piston washer. So I will describe this easy task first.

First, make sure the gun is not cocked and/or loaded.

Remove the trigger guard. This is done by removing the two or three (depending on the exact model of gun) screws holding the trigger guard in place and pulling the trigger guard free from the gun.

Next you need to unscrew the stock/trigger block from the cylinder. (On certain early guns such as some ‘H’ The Lincoln models, there may be a fourth screw holding the trigger block in place. You will see this on top of the compression cylinder just ahead of the trigger block. It also needs to be removed if present)

At this point it is advisable to have the end of the gun barrel placed against the floor (on a suitable pad to protect the muzzle crown). Using this technique you can lean on the stock continuously as you unscrew the trigger block and use your body weight to control the mainspring tension. (Some people prefer to clamp the cylinder in a soft jawed vice to leave both hands free to release the trigger bock).

You will need to pull the trigger back a little as you start to unscrew the trigger block away from the cylinder, but only for the first few turns, after which you can release the trigger. As you get near the end of the thread brace yourself to contain the sudden spring tension as the trigger block separates from the cylinder.

Once you have removed the trigger block/stock combination, you can gain access to the mainspring and piston. The spring guide on these guns forms part of the trigger block, so there is no need to worry about this being a separate component. Once the mainspring is removed, you can then go on to remove the piston.

In order to remove the piston from the compression cylinder, you first have to remove the short auxiliary cocking lever, just behind the larger hand cocking lever. This is done by unscrewing the auxiliary cocking lever pivot screw (and keeper screw if present), pulling the front of the lever down and disengaging the rear end from the cocking slot.

Once this has been achieved, a small screwdriver can be put gently through the cocking slot to push the piston back towards the rear of the compression cylinder eventually to emerge at the end of the tube.

At this point you can also remove the primary hand cocking lever by removing the pivot screw and lock screw (or round pin if a later model). After disengaging the front catch the cocking lever, you should be able to remove it from its recess below the breech.

If you want to remove the wooden stock from the trigger block, you need to either remove the metal butt plate by removing two screws at top and bottom (early models) or to remove the small oval wooden plug on the base of the stock (later models).

(If a later model, the oval plug will be secured with two dome headed wood screws and beneath the wooden plug there should be a curved spring steel washer, which pushes on the wooden oval making it easier to release. If the wooden oval is jammed in the hole, proceed very carefully and do not try to lever the wooden oval out, as they snap across the grain very easily and replacements are hard to find and even harder to replicate successfully.)

Once you gain access to the area behind the butt plate/wooden oval you will see a long hole with the head of a slotted bolt at the end. To remove the bolt you will need either a long, large flat blade screwdriver, or a flat bar bit attached to a brace or pair of mole grips (the large screwdriver is easiest!).

Once the bolt is loosened fully the stock should slide easily off the trigger block, but pay attention to the metal locating peg in the trigger block (this is often rusted or badly corroded)

Re-assembly is the reverse of the dismantling procedure.

I have not mentioned dismantling of the loading tap, as this part of the gun shows many variations and I will explain the different sorts of loading tap types in another post.

Lakey

Thank you Lacey a very clear and informative post. Cheers, Melv