Chinese And Rusty (Tuning a Chinky! )

[T 20]

Hi Folks

About five months ago while I was rebuilding my rusty 77k my mate little Eddy showed up with another gun action he'd found in the scrap.


http://i1138.photobucket.com/albums/...9122011413.jpg


A westlake B2.

Now having read a few posts on various forums it would appear that most folks consider the B2 to be an underpowered piece of crap, but I was happy to get one.

A lot of my Farmer Palmer type customers seem to own one of these little beauties having bought them years ago via mail order from this company.

http://www.bluemoonguns.com/Budgetrifles.htm

All of these B2 owners seem to ask the same question, "can you make this reet parfull ?"

So on and off for the last few months I've been experimenting with the action as and when I've had time, the thing that kept me interested was the fact that the B2 has the same swept volume as an early 77 so should easily make 12ftlbs.

Well after a bit of final tweaking today I've got this on the chrono.


http://i1138.photobucket.com/albums/...9122011419.jpg


That's with the action bone dry using 15.42 grain pellets.

Superdomes are giving about 600fps.


Now it seems a shame to waste this little action after all that hard work so I thought I'd put it in a nice stock so I got this out and had a measure.

http://i1138.photobucket.com/albums/...9122011415.jpg

HW77

Spot on.

But that would be too easy so I'm going to mount the action inside a tube and then mount it in the 77 stock, in this way I can make the gun semi recoiless.

All I need to do now is get some 35mm OD tube with a 2.5mm wall and a Diana 52 scope rail and I can start putting it all together.



Should I get some therapy ?




All the best Mick

[jumbuck]

Put it back in the scrap. I rebuilt my B2 i bought new for plinking at BBQ get togethers. 12 months before the spring broke. I put a Webley Excel spring in it, it destroyed itself Spend £35 or what ever they are now and buy a new one for kicks

[Beagle Boy]

A lot of therapy yes lol will be nice though, why don't you go the full way and make sledge? Rocoiless? Be nice that. Atvb rob

[T 20]

A lot of therapy yes lol will be nice though, why don't you go the full way and make sledge? Rocoiless? Be nice that. Atvb rob

Hi Rob

It will in effect be a sledge system as the 29.6mm OD action will be inside a 30mm ID pipe so the whole action will be able to move backwards on firing.

I should point out that this was all done years ago by a chap who showed his recoiless guns in AGW.




All the best Mick

[uk litehammer]

Now I'm a Chinese fan, but therapy sounds reasonable.

[Beagle Boy]

Hi Rob

It will in effect be a sledge system as the 29.6mm OD action will be inside a 30mm ID pipe so the whole action will be able to move backwards on firing.

I should point out that this was all done years ago by a chap who showed his recoiless guns in AGW.




All the best Mick

Point well made, lol what you doing internals wise? Button the piston ect? Hope this turns out as nice as your 77 bud. Atvb rob

[T 20]

I put a Webley Excel spring in it, it destroyed itself

Yep that would kill an unmodified one very quickly.


The B2 comes from the factory with very simple design and construction fault to the cylinder which allows the piston to slam into the end of the cylinder if anything much over the factory spring is used.


Once I'd fixed that little problem using a lump hammer, punch and some Loctite 271 amongst other things the velocity shot up from 500fps to 600fps with a much reduced recoil and surge (Mr Tyler briefly notes this problem in January 2012s Airgun World).



All the best Mick

[Hsing-ee]

Yep that would kill an unmodified one very quickly.


The B2 comes from the factory with very simple design and construction fault to the cylinder which allows the piston to slam into the end of the cylinder if anything much over the factory spring is used.

All the best Mick

Tell us about that fault. Won't all pistons slam if the pellet has not gripped on tight enough in the last phase of the cycle?

[DNF]

Hi Rob

It will in effect be a sledge system as the 29.6mm OD action will be inside a 30mm ID pipe so the whole action will be able to move backwards on firing.

I should point out that this was all done years ago by a chap who showed his recoiless guns in AGW.




All the best Mick

Hi,

They move forwards as well remember

[auora5000]

Waste of a HW77 stock IMHO........

[johnbaz]

Waste of a HW77 stock IMHO........

+1


John

[uk litehammer]

The ukchinese forum hold an annual shooting comp called the "oddball". You should seriously consider enering that, as they don't come much more oddball than the thing you're building.

[T 20]

what you doing internals wise? Button the piston ect?

Atvb rob

I'm doing nothing flash Rob just an old School tune up and my normal O ring piston head.


http://i1138.photobucket.com/albums/...0122011428.jpg


And I'm using a Titan XS Meteor spring with a few coils off (B2 top, Meteor bottom)


http://i1138.photobucket.com/albums/...0122011429.jpg


When I get around to tuning my customers guns I'll nip up to Mr Knibb's place and get the right size springs as I've had to put shrink tubing on the spring guide on this one to increase its OD (bodge ).



All the best Mick

[amsniper]

Well I'd be interested in seeing how it turned out!

[T 20]

Tell us about that fault. Won't all pistons slam if the pellet has not gripped on tight enough in the last phase of the cycle?

Seeing as you asked Alistair

It's all to do with compression ratios

A 25mm HW77 has a swept volume of 39cc and a transfer port volume of 0.042cc

This gives a compression ratio of 928:1



A B2 has a swept volume of 40cc and a transfer port volume of 0.365cc

This gives a compression ratio of 109:1


I thought I'd increase the compression ratio of the B2 and see what happened.


So I sleeved the transfer port down to 2.5mm by hammering in a tapered brass bush covered in locktite 271

http://i1138.photobucket.com/albums/...0122011426.jpg


This raised the compression ratio from 109:1 to 280:1 and also increased the velocity from 500fps to 600fps with Superdomes.


Just to check this all out I removed the bush and ran again with a 4mm transfer port which put me back to 500fps.
I also tried a 3mm transfer port which took me to 560fps.
So I put the 2.5mm transfer port back in and the velocity went back up to 600fps.


The spring I'm using now is weaker than the original spring and I may have to shorten it a bit more after the barrel chop and final assembly.


This all got me thinking about other guns I have with about the same swept volume as the B2 so I've been having a measure up of my spare cylinders.

http://i1138.photobucket.com/albums/...0122011431.jpg

So far it looks like Hawks could do with the transfer ports bushing down so I'll have a go at one of them when I get time.



All the best Mick