BSA Improved Model

[jirushi]

Hi, I recently bought a prewar BSA.
From reading John Milewski's great book "The Book of the BSA Air Rifle 1905 to 1939", I think it is an Improved Model (A).
The serial number cannot be read entirely anymore; this gun must have seen some life / had rust. But it seems to start with 126. See photos.

It looked quite tired. I lightened the stock a bit with fine steel wool and alcohol (being extra careful with the chequiering), and it is now getting a few layers of CCL oil.
I have made the metal a bit blacker by degreasing with acetone and then using Ballistol Schnellbrünierung. Some parts hardly had any finish left, so I thought this way the gun would have more protection for the future.

However, the internals need more attention than the exterior.
Power is relatively low (about 6.6 ft/lbs using .177 7,0 gr RWS). And it doesn't feel/sound right. Not a twang, but more a "boing".
The leather seal doesn't look great. At one spot, it is clearly damaged.
The piston has three phosphor bronze rings. I believe these should help sealing, or perhaps they are meant to reduce friction of the piston in the cylinder?
I think they do neither of those.
I tested their sealing capacity by removing the leather seal, and moving the cylinder up and down the compression chamber with my finger pressed no the transfer port.
Air clearly leaked past the rings.
Furthermore, they seem to make the cylinder move less freely through the cylinder.
Not sure why they are there; probably a tinkering project of a previous owner?

Then the springs. Twin springs, but one of them isn't flat section. It has a loose fit over the spring guide, or in the cylinder. Not ideal.
Together, they are about 21 cm (8,3") long. It is (too?) easy to put the trigger block back on the cylinder. I would expect more preload.

Hopefully the tap is ok. I will test it when I have a good piston seal.
Something that I noticed is that my .177 pellets don't fall to the end of the hole in the tap. In my .177 Light Pattern, they fall deeper.
I have tried RWS Meisterkugeln and a few types of JSB.

A few things on the "to do list":
- find or make a replacement leather piston seal. The usual parts shops don't sell this early flat type. It is about 5,5 mm thick. I might have to find a thick piece of leather and a 1.1" round cutter. Or try a 1.1" cup type seal (although I think this will reduce the swept volume quite a bit).
- find a flat section spring, or a pair of them.
- decide what to do with the phosphor bronze piston rings.

Any advice/input is welcome.

Many thanks, Louis



This stock length works well for me


Piston rings and damaged leather seal

[Garvin]

Louis if the bronze rings aren't doing anything positive, couldn't you just remove them altogether and be no worse off than normal?

[draitzer]

To me it looks like your piston seal is the typical shallow cup shape with a filler washer.

I've not seen any reference to metal piston rings on these. Also your piston 'head end' may be longer than normal, as the slot usually intrudes into the 'head' portion. Possibly a custom tuner's creation?

My records show original twin springs were about 10" total overall length, with 21 coils each.

Some info on pistons, spring swaps, etc. is available on Danny's Gallery at:
https://forum.vintageairgunsgallery....l-tips-faqs-2/

Good luck!
Don R.

[Lakey]

Wow, another interesting BSA comes to the surface. Thanks for sharing photos.

I have heard of occasional BSA/Lincolns with Phosphor Bronze piston rings before, and Dennis Hiller depicts a drawing of just such a piston on page 19 of his " Collectors Guide to Air Rifles - enlarged fourth edition " so maybe it was a prototype/experimental thing that was dropped for mainline production. That piston was on a gun with a serial number 49209, and it was a .22 .
The piston does seem professionally made, and the finish is good, so it could have been the work of a professional gunsmith. Also it does seem an extreme mode for a home enthusiast to do.

If your compression cylinder is in good condition, and true in dimensions you would have thought that either the three rings, or the conventional leather piston washer would have been an adequate seal, but to have both seems excessive to me. The piston rings rely on a spring action to hold them to the cylinder walls, so that in itself would generate more friction for the mainspring to fight against. They also rely on proper lubrication to function, so a thicker oil than normal is needed I think.

The pellets not falling to the bottom of the tap is due to the fact that the 'Improved Model' was the first BSA to feature a tapered Tap. The earliest production guns had parallel taps, which in practice were difficult to load. The pellets needed a seating pin. The Improved models tapered tap was an improvement, allowing pellets to be loaded without a seating pin, however the taper wasnt as wide as later models.

In my experience, BSA seem to function smoother with spring pairs rather than a full length spring, however that pairs need to be quite soft. If the steel is too strong, the firing cycle of the gun is harsh. Last time I looked both Protek and Knibbs were doing the paired springs.

Thanks for sharing details of your interesting gun.

Lakey

[Benelli B76]

If the piston is of normal length I would think that the extended piston head needed to accommodate all those rings would be too long and would reduce power by reducing swept volume of air.

Baz

[trajectory]

That's a very interesting find.

Your photo is very good & shows the three split ring washers very well. Below the washers there are, on my screen at any rate, what looks to me to be two further brass coloured rings. Are they really thin rings or grooves around the piston that have picked up a coloured reflection or something like that. I'd be interested to know what they are please.
Looks a great find & I am sure will be of interest to fans of older BSA air rifles. Just makes you wonder how many others there might be that nobody realises they have...

If you have a UV light I wonder if that might help reveal the full serial number?

[jirushi]

Thank you for the input so far, gentlemen. Much appreciated.

@ Don R., thank you for the info on the springs. That is very useful. Also the link from Garvin's forum is fantastic, with the technical info/tips.
The leather seal is a flat disk, about 5.5 mm thick. I will pick up a 1.1" leather cup type piston seal today, which will probably seal better, but reduce the swept volume. We'll see.
I might have to find a thick piece of leather, and a metal pipe with 1.1" inner diameter, to make a new flat type seal.

@Lakey, thank you for your very interesting comments.
The piston also has a "star" stamped on it, near the skirt. I think it is original BSA, but the rings might indeed have been a gunsmith's work?
And is it best to push the pellets deeper into the tap, or is it fine to just drop them in and let the air pressure do the rest?
Unfortunately, I don't think that Knibbs or Protek sell the paired springs anymore. (Knibbs: "BSA Round Section Wire Mainsprings (Pair) Part No. STD20 ***No longer available" - Protek: only non flat section springs on their website).

@Baz, the overall length of the piston (rod not included) is about 114 mm (4.49").
The "height" of the head is about 18.5 mm (0.73"). Would be interesting to know if it is a standard size, or longer to accomodate the rings.









When in the cylinder, the bronze rings still have "gaps". Perhaps not the best fit?


The "star" is on many parts of the gun. I believe this was the case with these guns anyway? Not sure what it means (must have a look in the BSA book!).
The "0" is also under the barrel. Does this mean that the tap is original to the gun?

[jirushi]

That's a very interesting find.

Your photo is very good & shows the three split ring washers very well. Below the washers there are, on my screen at any rate, what looks to me to be two further brass coloured rings. Are they really thin rings or grooves around the piston that have picked up a coloured reflection or something like that. I'd be interested to know what they are please.
Looks a great find & I am sure will be of interest to fans of older BSA air rifles. Just makes you wonder how many others there might be that nobody realises they have...

If you have a UV light I wonder if that might help reveal the full serial number?

Thank you trajectory.
Great idea to use a UV light. I don't have one at home but will see if there is one at the vet practice where I work.
Below the three split washers, there are two grooves in the steel piston head.
They must have indeed picked up a coloured reflection.
To be honest I thought this rifle wasn't anything special, and it probably still isn't as the condition isn't great, but I like it anyway and hope to turn it into a good and accurate shooter.
Something that will help, is to put a little bag of lead shot in the recess in the stock, under the steel buttplate. BSA were fantastic to think of these things!
The gun is now a bit front heavy for me.

[trajectory]

jirushi thank you for explaining about the rings behind the three main phosphor bronze (?) ones. I thought it was most likely a reflection. As you said the leather seal looks a bit worn & chewed & a replacement should help things along. You also mentioned the friction between the three rings & the cylinder wall being a bit high & depending how tight they are it will sap some power. A moderately heavy oil might help, but then theres diesling to consider if too much gets picked up by the leather piston washer. You also mentioned that the rings don't close up that well & depending how well they do, as you say, will also cause losses, in theory if the gaps line up the air path will have less resistance & it will be a bit worse than if the gaps don't line up. Maybe it's more theoretical than actual compared to the losses of a poor fitting main seal.......?

With examples I have shot pellet seating doesnt seem to make much difference in accuracy, the main thing to me seems to be to make sure the pellet skirt is below the level of the tap so it does not get cut or damaged when the tap is closed. Pushing it all the way down should make things more consistent but in reality I've not noticed much difference between seating a pellet part way or all the way to the bottom of the tap.

I think it's an interesting example, have you any idea of its history?

[jirushi]

Thank you trajectory for your advice on pellet seating.

I will test the gun in the following days, with a few setups:
- new 28 mm leather cup type piston seal
- a number of springs (Protek advised a Meteor spring, which I have. I have also picked up another spring from a Diana. And then I will order an Airsporter spring)
- with and without the piston rings. Hopefully they will come off easily (without damaging them); otherwise I might have to leave them on.
- I will try to make/have made a spring guide to slide over the original one, as the springs mentioned above all have a loose fit over the spring guide

About the history of this gun: I bought it from someone who found it in a gunshop not long ago. That's all I know unfortunately.
The trigger block has more wear to the metal, and had a different/more faded finish than the rest of the gun. I wonder if it was on this gun originally...
It will never be a collector's piece, but hopefully it will turn into a good shooter.

Cheers

[trajectory]

On an improved model B I used an Airsporter spring cut to give about 1.5" pre load. The end was ground & polished up, might give you a starting point?


Cylinder/barrel & trigger block might be an original pairing despite how they seem to have aged differently; if the steel composition isn't the same perhaps it might account for the different look?

It might never look mint but It looks like one to hang on to

[jirushi]

On an improved model B I used an Airsporter spring cut to give about 1.5" pre load. The end was ground & polished up, might give you a starting point?


Cylinder/barrel & trigger block might be an original pairing despite how they seem to have aged differently; if the steel composition isn't the same perhaps it might account for the different look?

It might never look mint but It looks like one to hang on to

That's great to know, thank you.
Does your Improved Model B have an old leather seal, or a replacement? I have a feeling that the shallow cup ones from Protek will work best.
Good point on the possibility of different metals giving different looks.
Here is how it looked when I bought it:
(very dark stock, due to all those years of oiling and dirt, I suppose. And faded finish on the trigger block)

[trajectory]

That's great to know, thank you.
Does your Improved Model B have an old leather seal, or a replacement? I have a feeling that the shallow cup ones from Protek will work best.
Good point on the possibility of different metals giving different looks.
Here is how it looked when I bought it:
(very dark stock, due to all those years of oiling and dirt, I suppose. And faded finish on the trigger block)

Hi, the piston washer on that model B might be an original one. It looked intact & was supple so I didnt replace it & it seems to work pretty well. I tend to make them if I need them. It's a bit of fun if you have the time & the bought ones sometimes need conditioning & fitting so I end up fiddling with them anyway. Your woodwork looks to have cleaned up well. Some stocks have marks & large patches which are almost black in colour & are really deeply ingrained. They can be got out but it's often a long job to do so. Yours looks to be pretty good.

[jirushi]

Hi, the piston washer on that model B might be an original one. It looked intact & was supple so I didnt replace it & it seems to work pretty well. I tend to make them if I need them. It's a bit of fun if you have the time & the bought ones sometimes need conditioning & fitting so I end up fiddling with them anyway. Your woodwork looks to have cleaned up well. Some stocks have marks & large patches which are almost black in colour & are really deeply ingrained. They can be got out but it's often a long job to do so. Yours looks to be pretty good.

Thank you trajectory.
One side of my stock is a bit darker than the other; I must have worked less hard on the darker side! It was a lot of rubbing with the steelwool. In any case it's better than how it was. Making leather piston seals is something I should learn. For now I will order one from Protek.

Does someone know how to get the phosphor bronze piston rings off correctly?
I have tried putting a small tool in the gap of the rings, but this way I will deform the rings, if I pull them out. Perhaps that's the only way.
I would rather have a good leather seal and no rings, than both (as I have seen that air leaks past the rings anyway).

[trajectory]

Piston ring removal, Hopefully someone better qualified than me will be along to give some advice. In the meantime I think there might be something on YouTube, hopefully, have a look for servicing a Webley senior or mk11 Service air rifle as they have phosphor bronze rings. Only thing is if they are servicing them they may not remove them for re use or they might already be broken. They are brittle so in motor engineering you used to push a ring from one side & wiggle a thin shim in the gap that appears opposite, then you move around 120 degrees & repeat, then another 120 degrees till you have three shims in place holding the ring open. Then wiggle the three around till they are at 90 degree spacings, then insert a fourth one. The shims are small in width & very thin but strong enough to hold the ring open , just enough to slide off the piston. Well that's one way old cars were stripped down. Same might work for your BSA but wait till someone else gives you another idea. Maybe thin but strong plastic might be enough, cut from packing material?

BUT they are BRITTLE so research it well, & choose whichever method you think is best for you. Once broken its too late to go back. It's your decision.