My Mercury Ratting Rig

[T 20]

I am genuinely in awe of your skill set T20. It puts my attempts at engineering such as turning a swollen Scorpion piston head down with my cordless drill and a hand file firmly into context.
Good job I kept it quiet.
...Oops

No need to be in awe of me, Sir.

I just happen to have the equipment needed to do this lot and time on my hands to play.

Turning a Scorpion piston head down in a drill is about the same skill set but without the equipment so no one should be put down for making do with the tools they have to hand.


All the best Mick

[NickG]

Excellent work Mick 👍

[T 20]

Did you get any sleep last night, Mick, or did the noise keep you awake?

Funny enough, Tone,

I've had the munchies since recovering from Covid and as Shirl was out yesterday afternoon I fired up the BBQ and cooked 10 burgers and half a pack of bacon and pigged out instead of building up the Mercury.

But, this morning I heated the end of the Mercury cocking link and battered it with a hammer until it fitted the HW85 breech block.
I also had to alter the cocking shoe end of the link as the Weihrauch cocking link geometry is different to a BSA Mercury and the link was binding on the piston --- all good after a bit of filing.



Now the bit you're waiting for, with the same stroke as before, the same Spring and preload as before I fired a few pellets over the chrono.

Superdomes are now leaving the barrel at 630fp.

Hobbies are zipping along at 735fps --- no that's not a typo, 735fps.



As I haven't drilled and taped for the front stock bolt bracket or altered the stock to fit the new breech block yet I was firing just the action over the chrono --- it felt quite calm compared to some.

I have found out this morning that after all my efforts I managed to weld the cylinder onto the breech 0.5mm out of alignment with the cocking slot --- no big deal as the cocking arm floats by 2mm in the slot anyway.
What's more annoying is that the scope dovetails are 1.5mm out of alignment.
After carefully measuring the cylinder I found that BSA had machined the dovetails 1mm off centre at the factory.
Even the dovetails don't really matter as I fitted a one piece mount and it sat perfectly level with the top of the breech block --- I'm buggered if I know how that works, but I'm not complaining.


Now I know everything is working as It should I'll get on with bluing the action and altering the stock in the next week or so.




All the best Mick

[T 20]

Excellent work Mick 👍

Cheers Nick --- it keeps me out of trouble.

[jeff0100]

That's fantastic work Mick, it really is.

I have my old Mercury (I think it's a mk2) and it needs that bolt conversion. Do you need any special equipment to do it ?
I'd love to save it, as I've had it since I bought it new when I was 14.

The barrel seems out of line and it shoots to the right slightly, If I'm remembering right.

[Shed tuner]

is the new TP much shorter than std Mick ?
Wondering how much down to that, or to the barrel bore/pellet fit ?
oh, and of course the ridiculous cut out / groove / other ways to waste space at the end of the stroke....

Sounds like an awesome result either way.

[T 20]

That's fantastic work Mick, it really is.

I have my old Mercury (I think it's a mk2) and it needs that bolt conversion. Do you need any special equipment to do it ?
I'd love to save it, as I've had it since I bought it new when I was 14.

The barrel seems out of line and it shoots to the right slightly, If I'm remembering right.

Hi Jeff.

Though I've never done a breech bolt conversion on Mercury jaws I had a look at what's involved and a measure up of everything to see how difficult a job it would be.

Basically all you need is a HW35/80/90 breech bolt and nut, a 7mm ream and a tap the same thread pitch as the Weihrauch bolt, the Mercury breech bolt is 0.25" (6.35mm) OD, the HW35 type bolt is 7mm, the base of the Weihrauch breech bolt threads is 0.243".
The way I'd do it is to ream the left hand breech jaw and the barrel block out to 7mm --- these are originally 0.25" (6.35mm) so you're only opening the hole by 0.65mm.
Once you've opened the left hand fork out to 7mm I'd poke the tap in from that side to tap out the right hand fork --- this would effectively use the left hand fork as a guide to ensure the tap goes squarely through the right hand side.
One more thing you may have to look at is the machined flat in the top of the breech bolt, this could need deepening by 0.325mm (half of the 0.65mm increase in bolt diameter), this could simply be done with a Dremmel if it needed it.
Without the lock washers the HW35 type bolt and nut are spot on the right size for the job and would end up looking like the one that Johnbaz has shown.


All the best Mick

[T 20]

is the new TP much shorter than std Mick ?
Wondering how much down to that, or to the barrel bore/pellet fit ?
oh, and of course the ridiculous cut out / groove / other ways to waste space at the end of the stroke....

Sounds like an awesome result either way.

The HW80 transfer port ended up at 10.6mm long , Jon, and came to me with a 3.5mm diameter.

The old transfer port was 11.2mm long by 3mm diameter = 0.0791cc

The new transfer port is 10.6mm long by 3.5mm diameter = 0.1019cc

So on paper I've lowered the SCR and gained power, but in reality I think I've upped the SCR due to the unmeasurable lost volume round the Mercury breech plug.

Tonight I removed 10mm of preload from the spring and the velocities dropped, but not by enough.

Superdomes are now doing 610fps

Hobbies are now doing 705fps


Rather than chop the spring I'm going to machine the spring guide spring seat to lower the power some more.



All the best Mick

[jeff0100]

Hi Jeff.

Though I've never done a breech bolt conversion on Mercury jaws I had a look at what's involved and a measure up of everything to see how difficult a job it would be.

Basically all you need is a HW35/80/90 breech bolt and nut, a 7mm ream and a tap the same thread pitch as the Weihrauch bolt, the Mercury breech bolt is 0.25" (6.35mm) OD, the HW35 type bolt is 7mm, the base of the Weihrauch breech bolt threads is 0.243".
The way I'd do it is to ream the left hand breech jaw and the barrel block out to 7mm --- these are originally 0.25" (6.35mm) so you're only opening the hole by 0.65mm.
Once you've opened the left hand fork out to 7mm I'd poke the tap in from that side to tap out the right hand fork --- this would effectively use the left hand fork as a guide to ensure the tap goes squarely through the right hand side.
One more thing you may have to look at is the machined flat in the top of the breech bolt, this could need deepening by 0.325mm (half of the 0.65mm increase in bolt diameter), this could simply be done with a Dremmel if it needed it.
Without the lock washers the HW35 type bolt and nut are spot on the right size for the job and would end up looking like the one that Johnbaz has shown.


All the best Mick

Thanks for that Mick, I really appreciate it, but it's totally beyond me. I don't even know what a ream is

[T 20]

Thanks for that Mick, I really appreciate it, but it's totally beyond me. I don't even know what a ream is

It could be worth having a word with NickG then, Jeff.

[jeff0100]

It could be worth having a word with NickG then, Jeff.

Will do, thanks Mick. I think the old girl is worth saving.

[TonyL]

Hi Jeff.

Though I've never done a breech bolt conversion on Mercury jaws I had a look at what's involved and a measure up of everything to see how difficult a job it would be.

Basically all you need is a HW35/80/90 breech bolt and nut, a 7mm ream and a tap the same thread pitch as the Weihrauch bolt, the Mercury breech bolt is 0.25" (6.35mm) OD, the HW35 type bolt is 7mm, the base of the Weihrauch breech bolt threads is 0.243".
The way I'd do it is to ream the left hand breech jaw and the barrel block out to 7mm --- these are originally 0.25" (6.35mm) so you're only opening the hole by 0.65mm.
Once you've opened the left hand fork out to 7mm I'd poke the tap in from that side to tap out the right hand fork --- this would effectively use the left hand fork as a guide to ensure the tap goes squarely through the right hand side.
One more thing you may have to look at is the machined flat in the top of the breech bolt, this could need deepening by 0.325mm (half of the 0.65mm increase in bolt diameter), this could simply be done with a Dremmel if it needed it.
Without the lock washers the HW35 type bolt and nut are spot on the right size for the job and would end up looking like the one that Johnbaz has shown.


All the best Mick

Top information, Maestro.

[TonyL]

Funny enough, Tone,

I've had the munchies since recovering from Covid and as Shirl was out yesterday afternoon I fired up the BBQ and cooked 10 burgers and half a pack of bacon and pigged out instead of building up the Mercury.

But, this morning I heated the end of the Mercury cocking link and battered it with a hammer until it fitted the HW85 breech block.
I also had to alter the cocking shoe end of the link as the Weihrauch cocking link geometry is different to a BSA Mercury and the link was binding on the piston --- all good after a bit of filing.



Now the bit you're waiting for, with the same stroke as before, the same Spring and preload as before I fired a few pellets over the chrono.

Superdomes are now leaving the barrel at 630fp.

Hobbies are zipping along at 735fps --- no that's not a typo, 735fps.



As I haven't drilled and taped for the front stock bolt bracket or altered the stock to fit the new breech block yet I was firing just the action over the chrono --- it felt quite calm compared to some.

I have found out this morning that after all my efforts I managed to weld the cylinder onto the breech 0.5mm out of alignment with the cocking slot --- no big deal as the cocking arm floats by 2mm in the slot anyway.
What's more annoying is that the scope dovetails are 1.5mm out of alignment.
After carefully measuring the cylinder I found that BSA had machined the dovetails 1mm off centre at the factory.
Even the dovetails don't really matter as I fitted a one piece mount and it sat perfectly level with the top of the breech block --- I'm buggered if I know how that works, but I'm not complaining.


Now I know everything is working as It should I'll get on with bluing the action and altering the stock in the next week or so.




All the best Mick

The HW80 transfer port ended up at 10.6mm long , Jon, and came to me with a 3.5mm diameter.

The old transfer port was 11.2mm long by 3mm diameter = 0.0791cc

The new transfer port is 10.6mm long by 3.5mm diameter = 0.1019cc

So on paper I've lowered the SCR and gained power, but in reality I think I've upped the SCR due to the unmeasurable lost volume round the Mercury breech plug.

Tonight I removed 10mm of preload from the spring and the velocities dropped, but not by enough.

Superdomes are now doing 610fps

Hobbies are now doing 705fps


Rather than chop the spring I'm going to machine the spring guide spring seat to lower the power some more.



All the best Mick

Sounding excellent, Mick. Just some final fitting and tweaking to go. Annoying re BSA's "handywork", butifit works.

Very well done and an inspiring project.

[greenwayjames]

Mick quote - "It's a shame BSA went with an upgraded Meteor rather than the Mercury when they built the Supersport, Jon.
I suppose they were trying to copy Webley's success of upgrading the Hawk MK3 into the Vulcan ?"


I was told by a reliable source that the objective was to get a compact rifle which is why that trigger mechanism was used rather than the Mercury/Airsporter one.

[evert]

Great progress Mick, and your experimental numbers show that the Mercury has enough swept volume..

I'm looking forward to see how the gun performs on paper!