My Mercury Ratting Rig

[Shed tuner]

best airsporter tune is to chop the spigot, thread m8, stick on adapter for a diana 28mm seal, job done. +5mm stroke and a seal that actually works, transforms them.

[T 20]

best airsporter tune is to chop the spigot, thread m8, stick on adapter for a diana 28mm seal, job done. +5mm stroke and a seal that actually works, transforms them.

I've done that one, Jon, but I want to go further.



All the best Mick

[TonyL]

There's the thing, James.

The Airsporter and Mercury has the same bore and stroke as my Original 35 which is such a nice firing cycle it inspired me to have another look at my BSAs.

As the Mercury uses the same piston as the MK4-6 Airsporter, I'm hoping to upgrade my two Airsporter S when I've settled on a tune for the Mercury.



All the best Mick

best airsporter tune is to chop the spigot, thread m8, stick on adapter for a diana 28mm seal, job done. +5mm stroke and a seal that actually works, transforms them.

Any idea how the TP dimensions may compare between the Airsporter and Mercury, gents?

Also, I guess the tap on the loading tap versions of the Airsporter will drop the SCR drastically?

[Shed tuner]

yeah, the airsporter benefits from a sleave down too.. never looked at a merc port ?

[T 20]

Any idea how the TP dimensions may compare between the Airsporter and Mercury, gents?

No idea on the Airsporter yet, Tone, but what I can give you are the standard Mercury dimensions :-

Cylinder Bore X Stroke = 28mm X 65mm (1.1" X 2-9/16")

Available compression cylinder = 28mm X 95mm

Piston weight = 320grams

Transfer Port = 3mm X 11.2mm

Available Spring room when cocked = 110mm


The only difference on my rat gun are the stroke at 70mm and a piston weight of 314 grams.

The spring I removed was a 33 coil Spring with 3.1mm wire.

Another problem which showed up was the fact that the end wall of the cylinder has a hemispherical section machined from the centre of it.
I don't know if this is supposed to be there or is a machining cock up at the factory, whichever it is it creates a little more work as I'll have to make a P38 casting of the cylinder end wall and machine the piston head to match.

That's about as far as I'm going to get today while I stare at the piston and think about the job, but I have a good idea which way this is going to go --- new piston.




All the best Mick

[TonyL]

No idea on the Airsporter yet, Tone, but what I can give you are the standard Mercury dimensions :-

Cylinder Bore X Stroke = 28mm X 65mm (1.1" X 2-9/16")

Piston weight = 320grams

Transfer Port = 3mm X 11.2mm

Available Spring room when cocked = 110mm


The only difference on my rat gun are the stroke at 70mm and a piston weight of 314 grams.

The spring I removed was a 33 coil Spring with 3.1mm wire.

Another problem which showed up was the fact that the end wall of the cylinder has a hemispherical section machined from the centre of it.
I don't know if this is supposed to be there or is a machining cock up at the factory, whichever it is it creates a little more work as I'll have to make a P38 casting of the cylinder end wall and machine the piston head to match.

That's about as far as I'm going to get today while I stare at the piston and think about the job, but I have a good idea which way this is going to go --- new piston.


All the best Mick

Excellent information as always, Maestro.

Maybe nice to post those vital stats in Brucie's Bore, Stroke & SCR thread, if you don't mind?

Nicely enough dimensioned TP, methinks?

Hemispherical section in the cylinder end (head?) - does it think it's an internal combustion engine? Maybe this was where the term "dieseling" originated from?

Hope you get that addressed. Correcting that lost volume should improve efficiency no end.

[T 20]

That's about as far as I'm going to get today while I stare at the piston and think about the job, but I have a good idea which way this is going to go --- new piston.

Well after looking at the Mercury piston for a while, measuring a few dimensions and calculating some weights I've decided that I'm definitely going to have to make a new piston --- again.

There's some very weird designing went into the Mercury and Airsporter pistons which doesn't make much sense.
The distance from the front of the piston cocking lever slot to the front of the piston head is 37mm --- on a HW95 this measurement is 17mm, the weight of this 37mm of piston head is about 90grams and would be difficult to shed any significant weight from.
So it looks like it would be quicker and easier for me to machine a completely new lightweight piston body to screw the original BSA latch rod into rather than try to lighten the original Mercury piston.



All the best Mick

[Big Andy]

You know what Mick..if I had to get rid of all my rifles the one I would keep would be my Mercury, it’s been fettled by Ray Neil with a buttoned piston and double O rings and shoots lovely. One of the best rifles BSA ever made in my humble opinion, also the one I hankered after as a lad but could never quite afford.

[crowbar]

It will never be a Beat all so will you be Crying with the big "O" ring, Free falling with a Petty parachute seal or
a little piece of leather that's well put together?

Sorry I will take the Valium in future.

[T 20]

You know what Mick..if I had to get rid of all my rifles the one I would keep would be my Mercury, it’s been fettled by Ray Neil with a buttoned piston and double O rings and shoots lovely. One of the best rifles BSA ever made in my humble opinion, also the one I hankered after as a lad but could never quite afford.

I wouldn't argue with you over that Andy, it sounds nice. --- besides which you're bigger than I am and only live up the road.

Unfortunately, as my Mercury is at present it wouldn't get into my top 20 of guns to keep --- it's just plain nastiness itself.

I've tried double O rings in the past after reading a John Bowkett article on tuning the HW77 in AirgunWorld --- I always stick to just the one O ring now as I didn't get on with two.



I was looking at my Merc again this afternoon thinking 70 grams may be a bit over optimistic to remove from the piston weight in order to get the Mercury piston down to 270 grams.
Then I realised I'd already made a piston using an Airsporter latch rod for my prewar BSA, so after a quick strip I had the piston out and on the scales. :-

image.jpeg




By no real coincidence the prewar BSA piston is very close in length to the Mercury. :-

image.jpeg



So I'll definitely be building a new piston for my Mercury when I get time.






All the best Mick

[Big Andy]

I wouldn't argue with you over that Andy, it sounds nice. --- besides which you're bigger than I am and only live up the road.

Unfortunately, as my Mercury is at present it wouldn't get into my top 20 of guns to keep --- it's just plain nastiness itself.

I've tried double O rings in the past after reading a John Bowkett article on tuning the HW77 in AirgunWorld --- I always stick to just the one O ring now as I didn't get on with two.



I was looking at my Merc again this afternoon thinking 70 grams may be a bit over optimistic to remove from the piston weight in order to get the Mercury piston down to 270 grams.
Then I realised I'd already made a piston using an Airsporter latch rod for my prewar BSA, so after a quick strip I had the piston out and on the scales. :-

image.jpeg




By no real coincidence the prewar BSA piston is very close in length to the Mercury. :-

image.jpeg



So I'll definitely be building a new piston for my Mercury when I get time.






All the best Mick

I may be bigger but you are cleverer

[T 20]

I may be bigger but you are cleverer

I doubt that Andy --- anyone trying to tune a gun with a crap trigger isn't that clever.





All the best Mick

[T 20]

I doubt that Andy --- anyone trying to tune a gun with a crap trigger isn't that clever.

And a crap cylinder and a crap 5.6mm barrel as well.

I really must put a wanted ad up for a 5.5mm Lightning or Supersport barrel before I finish machining.

[TonyL]

Any progress on this, El Maestro?