...and now it's the HW90's turn...

[Robert_Lavin]

Work is quiet for me at this time of year so I have a reasonable amount of airgun time. The '77 is fettled but not quite finished, the '80 is too but might get some cosmetic work, so now it's time to turn my attention to the '90.

I chronied (is that a word?) it today and found that whilst it's power output and accuracy are incredibly consistent with FTTs and Superdomes, it is a bit low on power running at about 9.5fpe. This is about 0.5fpe down on May last year.

My initial thought is that I just need to put some more air in the ram. I have a pump that will give me 300psi, which I believe is enough for a non-FAC 0.22 '90 so all I need is the car-valve to HW90 valve (whatever that is) adaptor which I expect is a relatively easy find - no doubt a forum search will point me in the right direction.

But then I thought that it might be an issue with the piston seal or something else - there's no point filling the ram if the ram isn't the problem.

So does anyone know if there's any diagnostic stuff that I can do to determine where the problem is? The stripdown guide I've seen suggests a de-gas is needed before the ram comes out which makes sense from a safety perspective but if I'm going to do that, then I might as well just pump it up and be done with it.

Anyone had a similar experience? ...and can I just put ambient air with it's associated water vapour into the ram? It doesn't have to be nitrogen or something drier?

On a different note, my well used '80 is turning out to be the most accurate of the three of my HWs with, surprisingly to me, the '77 being the least. This doesn't make sense in my world. Thoughts?

Thanks again. I will endeavour to provide some help to others one day, but you all seem to know much more than I do!

Rob.

[bighit]

I have a slim jim pump and the connector.I got it with my theoben evolution when I bought it. never used it yet.

best fittings sell them. http://www.bestfittings.co.uk/shopexd.asp?id=634 connector

not sure if the pump your going to use will be up to it if its a shock pump for a bike.

and using a dive bottle is not safe.

[TonyL]

Hi Rob,

Sorry, can't help with the '90. However, amongst many other knowledgeable people, some of the Boingerpeeps at one of the Bashes last year were playing with adjusting the ram pressure to fine tweak the firing cycle and power. Someone will be along soon......

I'm a little intrigued with the '77. At the end of the day, '80s are very accurate, so no surprise there, but what did your fettle involve and what pellets have you tried it with?

[Robert_Lavin]

I have a slim jim pump and the connector.I got it with my theoben evolution when I bought it. never used it yet.

best fittings sell them. http://www.bestfittings.co.uk/shopexd.asp?id=634 connector

not sure if the pump your going to use will be up to it if its a shock pump for a bike.

and using a dive bottle is not safe.

It is indeed a shock pump for a bike. Is 300psi not enough? £85 for the pump (on top of £20 for the adaptor) seems quite steep.

[pelletcaster]

Here you can find some nice information about this type of AG.
Maybe more than you want to know.
/forums/showthread.php/144602-Just-pulled-an-HW90-to-bits-findings-and-a-few-observations?highlight=hw90
OK - for some reason I can't figure out at the moment I can't bring the whole link in here.
So put the following sequence on top of the above and get rid of the x..x: xhttp://www.airgunforum.co.ukx


Your pump should be sufficient to get some more pressure into the Gas-Ram.
No need for nitrogene - just ambient air.


As your gun has pressure and is working there is no issue with the Shrader-valve but you can get a new one (and other SP for this AG) from here:
http://www.airgunspares.com/store/ca...RAUCH/HW%2B90/


Please note - this type of GasRam is temperature sensitive.
So your 0,5 fpe decrease could well be due to low environment temperatue.

[bighit]

It is indeed a shock pump for a bike. Is 300psi not enough? £85 for the pump (on top of £20 for the adaptor) seems quite steep.

its around 348 psi as far as I can find.

you could try your shock pump but be aware, although they say 300psi some can't get near that pressure.



you might be better finding out frown wheirauch what the ram pressure should be as there is some saying 10bar and others saying 25/26 bar

http://www.airgunbbs.com/showthread....-with-PCP-pump

[Robert_Lavin]

Here you can find some nice information about this type of AG.

Please note - this type of GasRam is temperature sensitive.
So your 0,5 fpe decrease could well be due to low environment temperatue.

I did think that. It was colder today than it was in May.

[Robert_Lavin]

its around 348 psi as far as I can find.

you could try your shock pump but be aware, although they say 300psi some can't get near that pressure.



you might be better finding out frown wheirauch what the ram pressure should be as there is some saying 10bar and others saying 25/26 bar

http://www.airgunbbs.com/showthread....-with-PCP-pump

Hmmm. Might be a job for the RFD then. I'll try to tap Weihrauch for info.

[Robert_Lavin]

Hi Rob,

I'm a little intrigued with the '77. At the end of the day, '80s are very accurate, so no surprise there, but what did your fettle involve and what pellets have you tried it with?

Nothing major. I got it used with a too long square section (Ox?) spring in it. Binned that and put a current spring in from Chambers. Strip, clean, relube. I did notice that the rear (steel) spring guide was quite tight in the spring, it needed some encouragement. 25mm internals if that's relevant. FTTs and Superdomes.

It's not inaccurate, it's just less accurate which is contrary to my understanding of fixed vs break barrel.

Perhaps it's a technique thing?

[bighit]

Hmmm. Might be a job for the RFD then. I'll try to tap Weihrauch for info.

there does not seem to be any definite answers.

there is higher pressure rams fitted to later guns . The BEST Fittings pump kit comes with a 2 part Gas Ram Adaptor, which, when screwed together, fits the Weihrauch HW90 and Theoben rifles made since 1998. Most older rifles will use just the short main part of the adaptor.

 Eight to twelve brisk strokes of the pump are required to pressurise the hose, as this is fitted with a one way valve. This is necessary due to the high pressures involved. Some models run with around 700 psi (48 bar) others require 1000 psi (69 bar

http://www.bestfittings.co.uk/pdf/Th...ions%20NEW.pdf

hence why you need to find out direct from wheirauch or hull cartridge the importers.

[Robert_Lavin]

hence why you need to find out direct from wheirauch or hull cartridge the importers.

I contacted HC but they won't tell me.

"...There is no set pressure for the gas ram system, when filling you must check over suitable chronograph to obtain the working pressure less than the 12 FT/LB limit."

Without wishing to sound ungrateful, that's not really told me anything I don't know.

Am I likely to have better luck with Weihrauch?

Has anyone on here actually fettled one and knows a ballpark figure?

Rob.

[bighit]

weihrauch might.

my instructions says pump it 20/25 times (After the8 to 12 pumps to prime the hose) and then chronograph the rifle

 Unscrew the slotted screw at the rear of the action (where fitted).  Screw on the Gas Ram Adaptor finger tight, making a seal with the 'O' ring around the small thread of the adaptor. Most guns will require the use of the adaptor in its complete form, with both parts screwed together. Make sure that there is a sealing 'O' ring between both parts. Only guns produced before 1998 are likely to require the short configuration.  Connect the hose to the side lever pump and tighten the fitting with a 14mm (9/16”) spanner (wrench).  Now the hose can be connected to the Gas Ram Adaptor via the snap connector.  Eight to twelve brisk strokes of the pump are required to pressurise the hose, as this is fitted with a one way valve. This is necessary due to the high pressures involved. Some models run with around 700 psi (48 bar) others require 1000 psi (69 bar).  After twenty to twenty-five pump strokes, check the rifle on a good quality and reliable chronograph to avoid over pressurising the rifle. If this is ignored the piston crown may burn out or other internal damage may occur and consequently the rifle would need to be returned to the factory for service and or repair. See BEST Fittings Ltd disclaimer below.  On completion of the adjustments re-assemble any parts and replace any cover caps etc. and check all screws for tightness before returning the gun to active use

http://www.bestfittings.co.uk/pdf/Th...ions%20NEW.pdf



but I dare say it depends if you have the higher pressure ram or the low pressure one. and thats using the slim jim pump not any other pump.

you could try the weihrauch forum.

[TonyL]

Nothing major. I got it used with a too long square section (Ox?) spring in it. Binned that and put a current spring in from Chambers. Strip, clean, relube. I did notice that the rear (steel) spring guide was quite tight in the spring, it needed some encouragement. 25mm internals if that's relevant. FTTs and Superdomes.

It's not inaccurate, it's just less accurate which is contrary to my understanding of fixed vs break barrel.

Perhaps it's a technique thing?

Generally, you'd expect a 25mm '77 to be MORE forgiving of technique.

Obviously check all the basics....stock screws, maybe give the barrel a clean and try a few more pellet types.

The very tight spring guide could well have something to do with it, though. If making a guide isn't something you can do yourself, you could let Mr Tinbum have your spring dimensions and have him make up some nice, properly fitting guides / top hat. Or get a spring and guide kit from Tinbum or V-Mach.

[Robert_Lavin]

weihrauch might.

my instructions says pump it 20/25 times (After the8 to 12 pumps to prime the hose) and then chronograph the rifle

 Unscrew the slotted screw at the rear of the action (where fitted).  Screw on the Gas Ram Adaptor finger tight, making a seal with the 'O' ring around the small thread of the adaptor. Most guns will require the use of the adaptor in its complete form, with both parts screwed together. Make sure that there is a sealing 'O' ring between both parts. Only guns produced before 1998 are likely to require the short configuration.  Connect the hose to the side lever pump and tighten the fitting with a 14mm (9/16”) spanner (wrench).  Now the hose can be connected to the Gas Ram Adaptor via the snap connector.  Eight to twelve brisk strokes of the pump are required to pressurise the hose, as this is fitted with a one way valve. This is necessary due to the high pressures involved. Some models run with around 700 psi (48 bar) others require 1000 psi (69 bar).  After twenty to twenty-five pump strokes, check the rifle on a good quality and reliable chronograph to avoid over pressurising the rifle. If this is ignored the piston crown may burn out or other internal damage may occur and consequently the rifle would need to be returned to the factory for service and or repair. See BEST Fittings Ltd disclaimer below.  On completion of the adjustments re-assemble any parts and replace any cover caps etc. and check all screws for tightness before returning the gun to active use

http://www.bestfittings.co.uk/pdf/Th...ions%20NEW.pdf



but I dare say it depends if you have the higher pressure ram or the low pressure one. and thats using the slim jim pump not any other pump.

you could try the weihrauch forum.

Yeah, I saw those instructions and was quite alarmed at the amount of pressure in the gas ram. Seems like an awful lot just to chuck a pellet!

I'l pop over to the Weihrauch forum and cast about there.

[Robert_Lavin]

Generally, you'd expect a 25mm '77 to be MORE forgiving of technique.

Obviously check all the basics....stock screws, maybe give the barrel a clean and try a few more pellet types.

The very tight spring guide could well have something to do with it, though. If making a guide isn't something you can do yourself, you could let Mr Tinbum have your spring dimensions and have him make up some nice, properly fitting guides / top hat. Or get a spring and guide kit from Tinbum or V-Mach.

That is the route I'm heading down. Although, I'm not discounting opening the rile up and finding the spring has snapped or something.