I assume the HW90K Carbine has the same adjustable gas ram, just a shorter barrel.Well, I finally bought a HW90. There have been several posts about low power, hard cocking, weight and general tuning questions. I decided to bite the pellet, buy one, and figure out what’s going on. So I ordered a new .25 from AoA. I also ordered a Weihrauch HW90 pressure gauge and a .22 barrel.
The HW90 simply reeks of quality. The stock is gorgeous. I really like the distinctive checkering. I measured the overall gun weight at 4275 grams, or about 9.4 lbs. Funny, Weihrauch’s site says 4 kg, or 8.8 lbs. I didn’t actually measure the cocking effort but it was very high.
Gun overall = 4275 grams, or 9 lbs 7 ounces
Beech stock = 1224 grams, or 2 lb 11.2 oz.
Inertia piston = 48 grams
Front sight = 46 grams
Rear sight = 46 grams
Receiver and barrel assy without inertia piston, sights or stock = 2911 grams
I ran a series of tests, measuring the velocity at different ram bar pressure levels.
I used the Weihrauch HW90 pressure gauge.
To charge the piston I used a Hill Mark IV pump, and two adapters.
A Schrader to 1/8 BSPP adapter. Available from Best Fittings in UK.
A quick release to 1/8 BSPP adapter. From AoA.
You screw the two adapters together, and they connect the Hill pump and the schrader port.
The Hill pump’s gauge is meant for much higher pressure levels and doesn’t have fine resolution for this job. But it’ll get you pretty close to 26 bar in about 10 pumps.
You start high, and work your way down to the target pressure.
The Weihrauch pressure gauge is ideally suited for the job. You just screw it into the schrader port in the back of the gun. You take a reading by depressing the head. Each time you depress the head, it empties its small internal plenum, and takes a new reading. Doing so drops ram pressure about 1/4 of a bar. It’s easy to creep down to the target level.
I found the highest power (21fpe) is about 19 bar, not at 26 bar. Any higher made it harder to cock and dropped power dramatically.
For UK levels, 14 bar hits about 12 fpe.
I swapped in the .22 barrel and retested. The power vs bar curve appears the same for both .25 and .22. 18 bar is the sweet spot for both.
I set it at 18 bar. Cocking effort is now quite decent. I'm getting 800 fps with the H&N FTT .22 14.66 grain pellets. That's 21 foot-lbs.
I removed the inertia weight and checked velocity. It didn’t change velocity. Cocking effort and recoil also seemed about the same.
Comments
It’s extremely sensitive to bar levels.
The 26 bar limit is just an engineering maximum. I think the factory sets them all at 26, and expects people to tune them down themselves.
Ideally all HW90’s should be sold with the understanding that they need to be tuned.
IMHO, the sweet spot appears to be 18 bar. At that level you get maximum power, and cocking effort is very reasonable.
People say that gas-ram magnum springers have harsh recoil. I did these tests without the stock, holding the receiver with gloves. I found recoil to be comfortable, even at 26 bar. The bare gun without a stock, iron sights or inertia piston weighs only 6.4 pounds. It’s got me thinking about fabricating a aluminum stock. It may be possible to reduce weight to 7.5 pounds.
I ordered a Vortek piston seal, and may retest later. The inertia piston deserves a closer look.
To deburr the inside of the receiver holes, I use a swiveling deburring tool, and put it into a pin vise, see photo. It gives you the extra reach. It's long enough to reach through the hole from the other side of the receiver.
I didn't run any accuracy tests.
Conclusion - I love my HW90. I would hope that those discouraged by high cocking effort and low power take a second look.
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