HW90 potential

[scax]

Hi Marty! Yes, Krytox will not perform to nearly its full potential mixed with other greases or oils -- hence, DuPont says to remove all traces of other greases before application. The moly disulfide powder exception is due to it not being an oil or grease. Some Krytox is sold with it added where it floats in suspension and supposedly aids in high pressure applications. Now, another user has claimed that Krytox can cause dieseling, which is not correct. Krytox is inert in the presence of pure oxygen which is why it is often used in oxygen transfer commercial applications. So, it cannot "burn" which requires oxidation by definition. So, there is no risk of dieseling should a touch find its way into the compression chamber of my HW90. It can, however, be vaporized if exposed to high temps over a certain period of time. I don't have data on the temp required to vaporize Krytox in one millisecond, but would like to know. I suspect it would take an extremely high temp to do this. One interesting characteristic of Krytox is the ability to "cling" to metal when applied to cleaned metals. It appears to "stick" in at least a mono-molecular layer and persist. That's why, for instance, I lubed the stainless steel on my Mitutoyo calipers with the tiniest drop, rubbed it in, then wiped it off, but could feel the difference in smooth operation that persists. The Krytox I use is rated H1 which means it's OK to have "incidental contact" with food in food processing applications, but it still needs to be treated as something potentially dangerous in the presence of very high heat as the vapors are like those of teflon that is vaporized -- not good in high quantity and/or long duration exposure. Still, I play with it a lot. Just need to be respectful not to torch it.

 

[scax]

Gents,

I think something that we are all interested to know is something no-one has yet succeeded in establishing: to wit, can a modded HW90 shoot "accurately" at a highest possible muzzle velocity, as in 30+ foot pounds muzzle energy??? If it can, that would quite nicely bridge the gap between PCPs and springers in a way not previously seen. To be meaningful, we will have to define what we mean by "accuracy", correct? Or at least see just how accurate we can be at say 50 yards and beyond and ask ourselves, "is that good enough to some purpose, like hunting"?

Note: This test may result in confirming that the HW90 is only "accurate" when tuned down to 19 bar or so which gives around 20 fpe -- something that is the general consensus up until now.

What gives me hope that we may be able to prove something more is how my HW90 will now perform since it has been carefully epoxy bedded in three separate steps with the two, forward stock mount 5mm bolts being pillar bedded in steel sleeve bearings with even these 5mm bolts' threads coated in epoxy inside the bearings to make them into de-facto, custom shoulder bolts with near-zero clearance, thus, zero movement between shots.

What's the difference between a PCP and my HW90 or any springer, for that matter? The piston shocks, of course. Right? Without any piston shocks to deal with, PCPs are known to be supremely accurate in their best quality and at super high power exceeding anything possible in a springer, generally.

But, what if it can be proven that a springer can be practically as accurate as the best PCP in the range of 30fpe which my gun can currently do, as modded. What about 35 or even 40fpe as I am not averse to pumping my HW90 a bit higher than 26 bar just to see how it goes -- the mechanics are strong enough (in my admittedly "unsafe" "non-manufacturer-recommended" opinion only) to support much more than the 26 bar rated pressure -- the question is: how much is too much? As in, can I cock it and will it shoot straight and will more bar always equal more fpe? Clearly, this doesn't work with the stock piston seal. Mine melted and had to be replaced with the much more durable Vortek 30mm seal.

I plan to this point to only use my peep sights which some will say limits this study and I would agree. However, it also will show just how good (or bad, lol) this can be with just peep sights. Should the testing prove something meaningful, new and exciting, I may have to get a scope on this later to see just how good things can be at say 100 yds.

In theory, I see no reason why my HW90 can't do what they say can't be done. Just look at the battle between the battleships Bismarck and Hood in WWII.
Bismarck had 15 inch guns mounted on a ship heaving in sea waves, moving only roughly in parallel with its target, the mighty Hood, pride of the British fleet. With only its fifth salvo, the Bismarck sank the Hood at a distance of over 18,000 yards with a direct hit to one of its powder magazines. Now, the 15 inch guns had the ability to recoil as much as 4 feet (exact info unknown to me) in order to absorb the shock when firing such huge projectiles. And yet, it hits it's moving target at a distance of nine miles using a highly arc'd trajectory. Now, compared with that feat, can't we do a bit more at 50 yards? (harhar!)

We'll see. Anyone have a tiny battleship target to loan?

 

[scax]

Just a possible important added note to running an HW90 at high bar pressures: As some already know, there are two o-rings mounted inside the piston with one backed with a plastic backer to help keep the outer o-ring in place. OK. But what about when running the HW90 at really high bar, as in 26 and maybe even more? I suspect these o-rings are nothing special -- the average item one can buy at a generously stocked, old-fashioned hardware store. As such, I would be concerned that these o-rings may deform under high pressure, either blowing out or more likely, expand under pressure and then create too much friction on the inner, black compression rod that's mounted and secured to the rear of the receiver, and thus reduce theoretical pellet velocity due to very high o-ring friction. In fact, I recall that when I removed and cleaned these o-rings in my HW90, they felt rather hard and "grippy" -- not what you want there as likely nitrile at best. You want low friction, fluorocarbon o-rings, right? Long story short, I once had a warranty issue at GE involving high pressure oil pumps which were blowing out their seals, causing a mess in wind turbines up 80 meters in the air. The solution? We found that higher quality seals made of Viton resisted deformation under pressure much better than the stock seals. What is Viton, you may well ask? It is the o-ring equivalent to Krytox grease -- super durable and also made by DuPont. I'm going to get the specs on the stock HW90 o-rings and order replacements made of Viton to use in possible future testing. I seem to recall that some "very well stocked" hardware stores, actually carry Viton o-rings, usually in a yellow plastic selection case in their o-ring sections. I would expect pellet velocities "roughly" proportional to the square of higher bar pressures. As an example of this, my HW90 at 20 bar did 19fpe with HN 15 grainers, but did 30.7fpe at 26 bar pressure. Math predicted a maximum of 32.11fpe at 26 bar, but there are losses along the way. Now, with the stock o-rings, I think they would be compromised at high pressures, possibly even moderate pressures, and start adding unwanted o-ring friction, reducing theoretical velocity. Just something others may wish to consider who might want to also do some similar testing. Cheers to your Saturday, Charles
p.s. The attorney in me tells me to add that this is NOT a suggestion that it is safe to run your HW90 above manufacturer recommended limits. To do so will likely void your warranty and may result in injury or death. I am willing to run that risk, but need to add this warning in our brave, new world.

 

[MartyMcFly]

Just a possible important added note to running an HW90 at high bar pressures: As some already know, there are two o-rings mounted inside the piston with one backed with a plastic backer to help keep the outer o-ring in place. OK. But what about when running the HW90 at really high bar, as in 26 and maybe even more? I suspect these o-rings are nothing special -- the average item one can buy at a generously stocked, old-fashioned hardware store. As such, I would be concerned that these o-rings may deform under high pressure, either blowing out or more likely, expand under pressure and then create too much friction on the inner, black compression rod that's mounted and secured to the rear of the receiver, and thus reduce theoretical pellet velocity due to very high o-ring friction. In fact, I recall that when I removed and cleaned these o-rings in my HW90, they felt rather hard and "grippy" -- not what you want there as likely nitrile at best. You want low friction, fluorocarbon o-rings, right? Long story short, I once had a warranty issue at GE involving high pressure oil pumps which were blowing out their seals, causing a mess in wind turbines up 80 meters in the air. The solution? We found that higher quality seals made of Viton resisted deformation under pressure much better than the stock seals. What is Viton, you may well ask? It is the o-ring equivalent to Krytox grease -- super durable and also made by DuPont. I'm going to get the specs on the stock HW90 o-rings and order replacements made of Viton to use in possible future testing. I seem to recall that some "very well stocked" hardware stores, actually carry Viton o-rings, usually in a yellow plastic selection case in their o-ring sections. I would expect pellet velocities "roughly" proportional to the square of higher bar pressures. As an example of this, my HW90 at 20 bar did 19fpe with HN 15 grainers, but did 30.7fpe at 26 bar pressure. Math predicted a maximum of 32.11fpe at 26 bar, but there are losses along the way. Now, with the stock o-rings, I think they would be compromised at high pressures, possibly even moderate pressures, and start adding unwanted o-ring friction, reducing theoretical velocity. Just something others may wish to consider who might want to also do some similar testing. Cheers to your Saturday, Charles
p.s. The attorney in me tells me to add that this is NOT a suggestion that it is safe to run your HW90 above manufacturer recommended limits. To do so will likely void your warranty and may result in injury or death. I am willing to run that risk, but need to add this warning in our brave, new world.

Does the theoretical max output account for the transfer port diameter? I don't know what the optimum TP size is for a gas ram, but typical TPs are standardized to work for both .177 and .22. Coincidently, they usually max out at 20 FPE. I'm not encouraging modifications, but perhaps the HW90's TP is too small to achieve 32 FPE.

On a separate note, the Sig ASP20, was supposedly a very accurate 20 FPE gas ram. It's now discontinued but it would serve as an interesting comparison point in terms of accuracy, performance and powerplant dimensions.

-Marty

 

[scax]

Does the theoretical max output account for the transfer port diameter? I don't know what the optimum TP size is for a gas ram, but typical TPs are standardized to work for both .177 and .22. Coincidently, they usually max out at 20 FPE. I'm not encouraging modifications, but perhaps the HW90's TP is too small to achieve 32 FPE.

On a separate note, the Sig ASP20, was supposedly a very accurate 20 FPE gas ram. It's now discontinued but it would serve as an interesting comparison point in terms of accuracy, performance and powerplant dimensions.

-Marty

I don't know the limitations on the transfer port, but it does make me wonder. But regarding getting up to 32 fpe, I do have some news!
Just two days ago, recall I posted velocity and muzzle energy data on three pellets?
Basically, HN Baracuda 21.3 grain avg velocity 736feet/second or 25.63fpe; 2. HN field target trophy at measured weight 15 grains (also heavy). 5 shots: Vel: 960, 959, 957, 963, 959 fps = 30.7 ft lbs and Crosman Hollow Point at measured weight 14.4 grains (a touch heavy). 5 shots: Vel: 992, 999, 1002, 995, 1005 fps = 31.86 ft lbs

Well, I didn't add ANY more air to my HW90. It's still presumably at 26 bar, but maybe my new Vortek piston seal is seating in better.
New 5 shots strings which I repeated now show:
1. HN Baracuda 21.3gr with a new average velocity at 788 vs 736 just two days ago and this kicks the FPE to 29.38.... almost 4Fpe greater. Could my chrony be erring? I don't know, but time will tell.
2. HN FTT 15gr also has a new average velocity at 987 vs 959 or now 32.45 FPE -- almost 2 higher than two days ago.
I may see even slightly higher velocities in days to come, but I don't expect it as these numbers are already pretty impressive at 26bar.

Also, even though I'm a pretty strong guy, I've decided I don't want any more cocking resistance than I have now at 26 bar, so I don't think I will go higher, except purely as a quick check perhaps.

One thing I did do (which may or may not decrease cocking resistance at 26 bar and may or may not increase velocities based on lower o-ring Friction) is order this in a pair: https://www.amazon.com/gp/product/B01DGM4GIU/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 At $15. the pair, I think they are worth trying on replacing the Weihrauch part number 2030 o-rings that sit inside the piston. These are an unique pair that cost about 100x more than the stock nitrile pair. I went with these because they are a moldable inner ring surrounded by a very stiff PTFE sheath. The squish-able inner ring should hold pressure and the PTFE should make very low Friction which may increase pellet velocity and may reduce cocking resistance a touch. We'll see...!

 

[scax]

I hope these o-rings are the correct size to go inside the big piston and seal it, as I didn't break apart my HW90 to check and got the data on an airgun site. These are ID 15/16", OD 1-1/8" and cross section 3/32". Should anyone be able to check one lying about, it would be nice to get that reality check. Thanks. Here's a write-up on what they are that I saw on a sales website with this part number ORTEVT119:

"Encapsulated FKM O-Rings are comprised of a FEP fluropolymer jacket encapsulating a elastomer core made of FKM material. These encapsulated o-rings feature an excellent resistance to almost all chemicals and maintain their properties over long exposure.

Encapsulated o-rings provide the chemical resistance similar in PTFE o-rings, but also carries the elasticity of the elastomer core. They feature excellent resistance to weathering, a low coefficient of frictions, dielectric properties, and flexibilty.

FKM material cores provide a better compression set and chemical resistance than silicone counterparts."

 

[scax]

https://trp.co.uk/fkm-rubber-vs-ptfe/ I'm no scientist and you don't need to be one either to understand the quick and interesting read in that linked short article which specifically compares the benefits and problems of BOTH fkm (Viton) and ptfe (Teflon) o-rings. It even mentions as a best of all worlds solution of using precisely what I just bought for my HW90 -- Viton in a sheath of Teflon. Teflon has the lowest coefficient of friction of any solid known to man. But it's hardness makes it prone to leaking under pressure which would not be good in a ram air piston where you want to keep your air pressure constant.

Why all this? Well, in manufacturing it is often cost-prohibitive to use exotic materials which may have great benefits for which no-one is willing to pay extra because it's not the makers job to educate the world on why it's worth it -- so they tend to go with cheap lithium and superlube greases over better, high priced exotics and cheap nitrile o-rings instead of best possible.

Now, it's just an unproven theory at this point, but I am seeking best possible accuracy as well as power! in my HW90. So, I want to see what a lowest possible friction o-ring that can still be elastic enough to hold in your ram air pressure might do. At atmospheric pressure, nitrile o-rings might work just great, but we can't see or directly feel what's happening when we put those o-rings under 377 psi static pressure (26 bar) and then add gobs more pressure when cocked. We feel a dramatic increase in cocking effort going from 20 bar to 26 bar pressure. Is that all just increased air resistance we are feeling? Maybe. What if not? What if nitrile o-rings against steel starts adding high to very high friction as you increase bar pressure and the nitrile is being squeezed against the steel interface it is sealing and sliding against? Nitrile is not a slippery substance, but teflon is. So, we put lube on the nitrile and hope for the best. Then what happens when your lube migrates or dries or hardens over time? You see the problem. Just like cooking eggs in a teflon pan, you don't need any oil, but try doing that in a nitrile pan and you'll have egg all over your face -- haha!

So, I have a device to measure the pull weight required to cock my HW90 at 26 bar with the nitrile o-rings and I will take measurements. Then, I will put in the pricey o-rings, go back to 26 bar pressure which I will verify and then see if there is any change in cocking weight using the pricey teflon-sheathed o-rings. Also, I will watch with care on my pellet shot strings pre and post o-ring change. I want to see if there is any perceptible lowering of the average velocity string deviation. In other words, does the o-ring make velocity more consistent due to lessened and therefore more consistent o-ring friction based on the assumption that when you have lower friction and it changes shot to shot, the change can't be as high as a higher friction o-ring because you are dealing with so much less quantity of friction with teflon that the delta or change is inherently a tiny percentage of any change in nitrile friction. I believe the factory Weihrauch o-rings are just cheap nitrile. Great stuff, but it might be too grippy under pressure in our HW90s. Science. One may love it without being a scientist.

Wishing all a blessed day. Charles

 

[fishing43]

https://trp.co.uk/fkm-rubber-vs-ptfe/ I'm no scientist and you don't need to be one either to understand the quick and interesting read in that linked short article which specifically compares the benefits and problems of BOTH fkm (Viton) and ptfe (Teflon) o-rings. It even mentions as a best of all worlds solution of using precisely what I just bought for my HW90 -- Viton in a sheath of Teflon. Teflon has the lowest coefficient of friction of any solid known to man. But it's hardness makes it prone to leaking under pressure which would not be good in a ram air piston where you want to keep your air pressure constant.

Why all this? Well, in manufacturing it is often cost-prohibitive to use exotic materials which may have great benefits for which no-one is willing to pay extra because it's not the makers job to educate the world on why it's worth it -- so they tend to go with cheap lithium and superlube greases over better, high priced exotics and cheap nitrile o-rings instead of best possible.

Now, it's just an unproven theory at this point, but I am seeking best possible accuracy as well as power! in my HW90. So, I want to see what a lowest possible friction o-ring that can still be elastic enough to hold in your ram air pressure might do. At atmospheric pressure, nitrile o-rings might work just great, but we can't see or directly feel what's happening when we put those o-rings under 377 psi static pressure (26 bar) and then add gobs more pressure when cocked. We feel a dramatic increase in cocking effort going from 20 bar to 26 bar pressure. Is that all just increased air resistance we are feeling? Maybe. What if not? What if nitrile o-rings against steel starts adding high to very high friction as you increase bar pressure and the nitrile is being squeezed against the steel interface it is sealing and sliding against? Nitrile is not a slippery substance, but teflon is. So, we put lube on the nitrile and hope for the best. Then what happens when your lube migrates or dries or hardens over time? You see the problem. Just like cooking eggs in a teflon pan, you don't need any oil, but try doing that in a nitrile pan and you'll have egg all over your face -- haha!

So, I have a device to measure the pull weight required to cock my HW90 at 26 bar with the nitrile o-rings and I will take measurements. Then, I will put in the pricey o-rings, go back to 26 bar pressure which I will verify and then see if there is any change in cocking weight using the pricey teflon-sheathed o-rings. Also, I will watch with care on my pellet shot strings pre and post o-ring change. I want to see if there is any perceptible lowering of the average velocity string deviation. In other words, does the o-ring make velocity more consistent due to lessened and therefore more consistent o-ring friction based on the assumption that when you have lower friction and it changes shot to shot, the change can't be as high as a higher friction o-ring because you are dealing with so much less quantity of friction with teflon that the delta or change is inherently a tiny percentage of any change in nitrile friction. I believe the factory Weihrauch o-rings are just cheap nitrile. Great stuff, but it might be too grippy under pressure in our HW90s. Science. One may love it without being a scientist.

Wishing all a blessed day. Charles

Great post

 

[JayJay]

Oh yes, Krytox GPL-203 is highly popular to those lubing keyboards and another reason I include the good 00 brush which has a tiny head that works well in that application as well as all tiny places I use Krytox -- I still manage to waste more than stays where I need it, but a little lasts so long. Another popular use is to lube and protect car window trim and sunroof glides. It's important to remove all traces of prior oils and greases. I tend to use brake parts cleaner as the last step ahead of Krytox application. However, pure moly disulfide powder works well combined with Krytox so long as you don't mind how it stains your clothes... haha.

Interesting. Some Krytox, such as GPL-216 comes pre-mixed with moly. They use it for super-high pressure applications. But GPL-216 is more viscous than 203. That might be a good choice for airgun cocking linkages. The HW30 and HW50 occasionally get linkage galling. I haven't seen any galling in my HW90 but you never know.

Piston and seals don't experience super high pressure, so something a little less viscous like GPL-203 is probably better there. I like the fact that GPL-203 is inert in high oxygen environments, meaning it's not going to diesel.

I discovered that GPL-203, 205 and 206 are H-1 certified. I think that means they're acceptable as a lube in food processing equipment. That may explain why it's popular in computer keyboards. It's also a plus for airguns, which get lots of handling.

How easy is GPL-203 cleanup? It's supposed to be insoluble.

 

[scax]

All agreed, JayJay! Now, on GPL-203 clean-up, it matters just how clean you need something to be. About half the time, I dab my index finger in my Krytox tin (like a pellet tin, but much smaller and nicer looking with a clear window to see what's inside) which is perfect for quickly dabbing just a tiny touch and then spreading it on a large surface. When done, I have a finger (or three!) whetted with the stuff. As it's thin, I can wipe most all off my fingers with just a paper towel, then warm soap and water, then rub hard with a terry towel cloth and enough is gone that I don't worry about residual remaining. As you say, it's H1 cleared, so I don't worry and never had any ill effects in using it these past 35 years. Now, I also use Krytox LVP which is MUCH thicker and stickier and I try not to get that on me, but do the same to get it off. It's a better grease in places like hinges and high pressure applications as it stays in place better.

Now, if by clean you mean you want to remove every possible trace of krytox from say, a metal surface, I recommend scrubbing and rubbing with extremely hot water, but it won't get it all. Dupont sells a very pricey solvent, but I've never needed it in all these years.... I've always been pleased with everything I used Krytox on with only one exception, in which case I did have to clean some threads on an astronomy mount project that I wanted to re-lube with Nyogel 767A which is silica-thickened lube gel used to give a super-smooth and slow turning feel to threaded controls. I didn't get all the Krytox off, and it compromised the Nyogel to some degree. The project was still a resounding success as I later sold that telescope mount and the buyer said he was very pleased with its action as modded.

And correct on the GPL being a good choice on the piston and o-ring seals. When I switch to the new teflon-coated, viton seals in a week or so, the 203 will serve mostly as a sealant to assure air molecules stay in the ram since the teflon should give the piston a VERY slick ride.

I never did think about the trigger linkages -- I'll take a look at mine soon. Thanks. I did put a very thin coating of 203 in the sear, however. My trigger was too unpredictable as it came from the factory -- too light, as well. I applied a special drying lube called Eezox to the trigger internals, tightened the adjustment screw and put blue Loctite on it and then blasted all excess lube out of the trigger housing with brake parts cleaner --- and now, to my pleasure, I no longer get any "surprise" shots and I can always predict when it will go to give that last, tiny extra when the sights align momentarily on target. Highly unorthodox, but it worked.

 

[scax]

Another thing about Krytox, since you got me on it again, JayJay! It is not only inert, but it doesn't dry out -- ever. What this means is that even if it's not the very best lube, it ages well. It won't get worse just because it sits like so much lube does in airguns which locks them up over time. I recently replaced all the door lock mechanisms on my big old GMC '99 Suburban which still looks sharp. Well, what ruined those electronic door locks was grease! The steel linkage rods which went through plastic guides were greased, likely when produced . Had they never been greased, the locks would have never been stressed to failure, as the plastic guides weren't likely to bind. However, the hydrocarbon-based grease applied to the plastic guides turned truly into the stickiest glue you can possibly imagine and the binding burned out the electronic locks. What a pain to replace them, too. And getting that old grease removed took more time than replacing the locks! Krytox would have never turned to glue and the amount needed to lube all would have cost only about $10 in bulk as only a touch is needed. But I digress. Krytox. It's expensive but you know what they say: Kry once and .... haha!

 

[JayJay]

Gents,

...

But, what if it can be proven that a springer can be practically as accurate as the best PCP in the range of 30fpe which my gun can currently do, as modded. What about 35 or even 40fpe as I am not averse to pumping my HW90 a bit higher than 26 bar just to see how it goes -- the mechanics are strong enough (in my admittedly "unsafe" "non-manufacturer-recommended" opinion only) to support much more than the 26 bar rated pressure -- the question is: how much is too much? As in, can I cock it and will it shoot straight and will more bar always equal more fpe? Clearly, this doesn't work with the stock piston seal. Mine melted and had to be replaced with the much more durable Vortek 30mm seal.
...
We'll see. Anyone have a tiny battleship target to loan?

Well, the HW90 is already at the top of the power heap.

At 26 bar, our HW90's reach about 31 fpe with .22 Crosman Premieres. Only one gun that beats that. The Theoben Dual Magnum supposedly reaches 24 fpe with the first stroke and 36 fpe with the second stroke. Here's a link that compares the Dual Mag with the Eliminator and the JW80 Whiscombe. Dualmag-Eliminator-JW80

The Hatsan 130QE is rated around 30 fpe, and the Gamo Swarm at 28 fpe.
5 powerful airguns

I'm not much of a marksman. At higher power levels the HW90 seems to be hold sensitive. I tried some runs while gripping the stock as hard as possible, vs lightly resting it on my palm, and got different results.

I would stay away from over-pressurizing. It's an 'unsafe practice' and we should probably not discuss that on this website. Most manufacturers give you at least a 5% safety margin, but there's no way to know. Anything over 26 bar is potentially dangerous

However, I have been curious about the tiny little 7mm barrel pins that Weihrauch uses. Can they really carry all that load? So I did some 'back of the napkin' calculations. I assumed a piston pressure of 26 bar, a piston diameter of 30mm or 1.18", and a barrel pin diameter of 7mm or 0.276". The pressure is 26bar * 14.7in^2/bar = 382 psi. To calculate the force on the piston we need its area. Area is PI*r^2 or PI*(1.18/2)^2 = 0.349 inches^2. The force is pressure times area or 382 psi * 0.349 inches^2 = 133 lbs. The pin carries half on each side, or 66.7 lbs per side. The pin area is PI * (0.276/2)^2 = 0.019 inches^2. Load is force divided by area or 66.7 lbs / 0.019 inches^2 = 3511 psi on each side of the pin. But how strong is steel? Mild steel has a yield strength around 40k psi. Shear strength is 70% of that or 28k. Fatigue limit is 40% of that or around 11k psi. 3.5k is well within that limit. I'm mighty rusty at this stuff, will be happy to eat my hat if I got it wrong.

The cylinder is another issue. Even if the wall thickness is enough to handle 26+ bar, we don't know how the forward end plug is fixed. Maybe it could blow out. Also, the trigger latch might deform. I have seen my share of sudden mechanical failures.

Anyway, it's all fun.

 

[JayJay]

....Moderator edit to remove For Sale post outside of classified section....

Holy Moly, 30 pounds. Now I understand. What is the volume of 1/2 ounce?

 

[scax]

Holy Moly, 30 pounds. Now I understand. What is the volume of 1/2 ounce?

At a density of 1.92 grams/ml, 1/2 oz is roughly 7.39 milliliters by volume, right? When applied judiciously, it lasts a surprising long time unless it's being used for auto window/door gasket lube and preservation.....that can use quite a bit but it works good to rejuvenate them and preserve old rubber from oxidation.

 

[scax]

Well, I took some cocking weight measurements today and the average high (which occurs just as the safety is engaged) was 24Kilograms, but the very first reading which I excluded was 27.15kg -- the gun hadn't been cocked in a day. Regardless, those are pretty high readings. I get in my new piston o-rings on Thursday, so hope to have interesting results to report by the weekend.

Looks like we have a kind moderator who liked my last post, but asked me to post my prices on anything to sell in the classifieds -- will do.

Also, I think my HW90 is dieseling something. I cleaned the barrel bore with Silikroil and I know some went into the barrel breech recess by mistake and I think some is being sucked into the compression chamber, perhaps via suction created by piston rebound-- a few insane readings on the Chrony. I backed off to 25 bar, but same thing. I'll check it all good when I have it apart to install the new orings, but I can smell the Silikroil which has a distinctive odor. My guess is it burns real good but I need to take care to get it out. More teething pains. At even 25 bar, cocking was noticeably easier than 26, but no readings taken yet at that pressure.

 

[boscoebrea]

That was a fun read and I don't even have a HW90

 

[scax]

Yeah, it was cooking some Silikroil, pretty sure now. I carefully pulled out the breech seal and sure enough, it was wet with Silikroil. Not only that, but there was a thin layer of oxidation (rust) around the transfer port which came off by rubbing with a toothpick and wiping with a paper towel. Water (which forms rust) is a by-product of burning oil as in dieseling. I also noticed that the way the barrel is mounted in its block, there is room enough around the barrel to suck in some Silikroil and it was wet where I could see it there, as well. So, I have my barrel opened and resting on a chair with the breech end facing down for the night to see what drips out. No worries -- no children here.

That 27.15Kg reading I mentioned in my previous post...... I wonder if it was the rested piston seal giving more resistance or the piston o-rings. My bet is on the o-rings which could drive out the lube just sitting and put nitrile to steel which grips overnight. The second reading was just 23Kg, but it varied with each cocking by as much as 1.9Kg and I think that's significant.

More testing to come....

 

[scax]

The piston....
Nicely machined, rather heavy, it plays a large role in determining whether or not the gun will put one pellet into the hole of your previous shot.

In this pressurized, air ram design of the HW90, we want the piston to move exactly the same, shot to shot, otherwise accuracy will surely suffer as accuracy is nothing other than repeatability in all variables, over and over again.

Now, this design benefits because the piston is well supported at the rear, inside, by two orings riding on a more or less fixed shaft of 24mm diameter, if memory serves. More or less because the 24mm shaft is not rigidly fixed in position, but can wobble slightly by the way it is installed into the rear of the receiver. Not perfect, but I think the idea was to allow a touch of wobble so the piston seal in front could better hug the walls as it zooms forward toward the transfer port. The piston seal is doing a lot of work....guiding the piston front forward against the 360 degrees of the inner walls along which it must ride AND compress all the air in front of it AND keep the sides of the steel piston from dinging the same chamber walls en route. That's alot to ask of one component. Though it seems to do the job, maybe it could use some help?? I noticed that my piston has been machined, just behind the piston seal area, with a lovely groove around its circumference to accept a rather wide o-ring, but none is there! Hmmm. Kinda makes you wonder if one engineer said: "We must give ze piston seal Zum helps". But then the accountant finds out what they've done and said:" Nine! Are you crazy? Our profit on this gun ist already caput!".....so, no seal, but the groove looks just too goovey not to give it a try with the same type of pricey Teflon encased Viton o-ring. It "could" better keep the piston -rocket perfectly centered on its quick ride to the transfer port. It could also help the piston seal to not lose any air in blow-by, due to an imperfect piston seal. I would like to think it would make for a more repeatable amount of air getting compressed shot to shot, due to no blow-by. I mean, they already cut the groove at the factory. I will be taking my HW90 apart again today or tomorrow. When I do, I will see if an o-ring can be found to fit.

Could end up doing no good, but on the other hand....ja ja, das ist gut!! Haha!

 

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Above is an image courtesy Pelletcaster on AirgunBBS of an HW90 piston, quite like mine. Look just behind the red piston seal and you will see the unused groove that seems sized to fit an ORTEVT023 o-ring which is 1-1/16" ID Nominal X 1- 3/16" OD Nominal X CS Nominal 1/16" -- just a smidge oversized to work in the HW90, but as this seal has some elasticity, I ordered one to see how it goes -- to arrive on Monday. Same material as the other two ordered to go inside this piston. The groove is there. Why not use it? Could be Weihrauch didn't as inexpensive o-rings could have caused more harm than good. The nice o-ring cost just $7.11 shipped Prime. But that is about 100x more than sticky nitrile equivalents. We'll see how it goes -- stay tuned.