Hi HW90 owners and prospective owners. Because of the lack of info out there about the pitfalls on owning this rifle I wanted to put out my version so that it might get more people thinking that they WOULD like to buy this rifle.

Because I really like it.

INCIDENTLY, with Theobens exclusive patent ending this year, lots of companies like Crosman are making their own "Gas Rams", so you will expect to see alot more of them on the market.

The HW90 is a single shot, break barrel, self contained gas spring airgun made by Weihrauch of Germany in cooperation with Theoben of the UK. It is a heavy airgun at over 11lbs with a scope, silencer fitted. Beeman of USA also made one as RX1 and RX2. The safety is resetable. At 26bar the airgun is tough to reload each time. You can also get a carbine model HW90K. Heres a data summary.>>
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Model HW90 26bar .22 Cal Weight 11lb Length 117cm Velocity fps 620-840fps Muzzle Energy 19-20 Cocking Method : Break Barrel Cocking Effort Heavy Recoil Rating Heavy

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If you buy one, and intend to maintain it yourself, buy some piston and breach seals. The rest can pretty much be sourced.Theoben sell pumps so do Hills, but get a pump with a dial otherwise changing the pressure may be hit and miss. There are many DIY pictures out there of how to disassemble one.
I own a HW90, 0.22cal (5.5mm). I adjust my own pressure. Mine is pumped up to 26bar with a shock pump made by Scott Pro. The pressure gauge on it (0-40bar) has been calibrated with my own reference pressure gauge. I found the pump pressure gauge to be reading 1bar low over the pressure range.
I've also tried the HW90 at 12,15,20,22,26bar. It does not fire at all at 5-7bar. I keep the airgun at 26bar because thats how this theoben gas spring is specified (over 20 ft-lbs energy).

Shooting Position:At 26bar, it is a tough rifle to master.
But most of the problems of inaccuracy come from shooting position.
Look at a You Tube video called "FT shooting positions". Excellent video.

None of this elbows on knees stuff.
Accuracy is particularly important with rabbits (40-50m) and you need to get that head shot ,otherwise they will go into the burrows. And perhaps die there needlessly. Seeing the video changed my mind about the HW90.

Vibration: At 26bar every screw and nut vibrates free. You must loctite them all (silencer grubs, scope mounts, HW90 nuts,use loctite 342 or better).

Scope mount: I use sports match AO mount (4 allen key bolts, similar to Beeman 5039). Setting it up properly is crucial, otherwise you may run out of windage and elevation on the scope. If I could, I would try a BKL260 mount (6 allen key bolts) with 4 to 7/1000" droop, to compare.
But they are not available worldwide. (although I've hearld the BKL has been bought out and is being resurrected in 2009!!)

Scope:I use Leupold scopes like the EFR types. So I don't need a dampa mount.

Moderator:I have fitted a Weihrauch silencer, because I feel the HW90 at full power is noisey. Straightshooters have a RX1 0.20cal as 69dB at 50yards. I'd expect more for a 0.22.
To fit the silencer, it fits straight over the front sights. No cutting off of the barrell required. I made a neoprene tube made from a dive suit, to fit over the silencer to stop it getting scratched.

Sling:You must have a sling as it is heavy. To fit the sling at the receiver end, I had to drill a 2-3mm hole into the cocking arm (all other solutions were budget). I then threaded stainless steel tackle( used to catch big game fish), multiple times into small loops through the hole while also threading into PVC tube at the same time.The PVC tube stops the wire from ripping into my leather sling loop).

Schrader Valve: When you undo the blanking screw from the end of the air fill port you will could hear a escaping air sound. That comes from a leaking schrader valve. You should find it to be a pink/red coded type. I believe that this valve is not correctly rated for the rifle at 26bar (377psi). You need to replace this valve with a higher rated valve (white coded) as fitted to aircraft tires (they are rated at over 400psi).
I did this and have had no more air escaping.

You won't read this claim about the valve anywhere else on the internet. But thats what I've found.

Reliability: There are lots of stories out there about the unreliability of the HW90. Alot of it I believe is mistreatment. Anything from filling the rifle with Oxygen, to allowing it to rust, to contaminating the receiver with soil and dirt. Mine has been shot over 3000 times in less than one year. Don't dry fire it, or let the receiver go while cocking it until it clicks, and you will be doing all you can to give it the best chance of survival.

Pellets:I use JSB/Wolverines/Air Arms in the 16gr to 14.3gr (jumbo express) range, all domed and the results are consistant. Typically, 2 inch groups is a good outcome at 50meters. A rabbits head diameter.That's full power of over 20 ft-lbs not 12.

About pellets grains for this gun. I asked Charlie de Tuna in the USA about heavier or lighter pellets, and he seems to think that its best to stick to the mid range pellets. Up to 18gr. So the Barracuda of 21gr is not favoured.
In essence though, getting the flattest trajectory out of a pellet without the associated instability caused from bad aerodynamics and high speed is what the goal of pellet selection is all about.

Rust: You must wipe the metal with good gun oil. Regularly.The bluing can deteriorate even if you look after it. A good wipe down is a good routine to get into.
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Webb sites
Look at this webb site about Hunting THEOBENS in 0.22cal

http://www.velocitypress.com/air_rifle_ballistics.shtml

Shock Pumps and Misc

When in Eastern Europe I was looking for a shock pump to 26 bar.
As you can see there are many below that. There are two that are cheap.
First preference is = BETO shock pump 28bar.
Second Preference = Scott Pro 40bar.
I could not find a Beto so I settled for what I could get. Thats the Scott.
Secondly the Scott comes with a Female Schroder valve. The Hw90 comes with a thread that is difficult to decipher in the first instance.
I did buy a original weihrauch pump hose (its yellow).
Then a local fitter and turner engineer reversed engineered the pitch on the other end of the weihrauch hose, and made a thread for it from a stainless steel blank. On the other end of the same stainless steel blank, a schroder MALE thread was cut. Which is easy peasey for these guys to make.

More Notes about the dials on these pumps.

Some pump dials could only have accuracies of 1% or 1.6% or 2%.
On my 40bar that would translate to an error of +-0.4bar , +-0.7bar, +-0.8bar...mine was at least 1bar low.
That means to fill the HW90 to 26bar my dial had to show 27bar.
Thats (1/40)x100% = 2.5% error--> These dials are nothing special so its better to UNDERINFLATE than OVERINFLATE.

Pellets/Managability of Recoil

My HW90 is original and pumps to 26bar as stock standard. If you have 26 stamped on the HW90 then you have the same seals as I do, except you may only have 15bar in the chamber to give you 12ftlb.
Most sites I have seen have the owners maintain them at 20bar. They claim the shots are more accurate and managable. Thats true but the weight is still the same. For me a drop in the barrel during a shot is because of my loss in concentration because of the barrel weight.
Also, reducing the pressure from 26 to 20bar (23% reduction) should result in 23% less wear, for the same pellet weight.

If you want to manage the wear of your air rifle then use only pellets in the mid weight range!
Too light - max piston slam , also pellets exceed their intrinsic terminal velocity and become unstable in flight. That's because unlike rockets they don't have an automatic guidance system, so after a bit of cartwheeling, they may hit your target on their side and be way off target.
Too heavy - pellet takes longer to leave bore - pressure sustained in bore longer --> temperature sustained in bore longer --> greater opportunity for heating of piston - more chance of diesling --> piston seal melt?
If you don't believe that, then why are over pressurised HW90s having their piston seals melting, even for mid ranged pellets. (this is the case where we leave the weight of the pellet as it is and increase the pressure instead)

Parts

Thankfully, I have never had to make any major repairs on the HW90.
Maintenance may be required of the schroder valve and breech seal.
My valve failed the other day (thats the high pressure 400psi) but I replaced that with my own remover which I made from a small stainless steel tube with a small slot at one end to fit over the valve groove and a handle TIGed onto the other end.
(minimum you must have Piston seals and maybe breach seals).
In fact keeping aside these parts, are my insurance against the price increases and lack of availability of parts.

see my review on servicing the HW90