HW55: making piston seals and general rambling.

Recently acquired a HW55T that was a little tired. I made an adapter and popped on a synthetic seal at first, then decided to try and go back original and replace the leather piston seal. Didn't want to order one, so I got an idea and whipped one out with junk I had on hand.

Here's the synthetic seal adapter:

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Here's my leather seal manufacturing tools. Anybody recognize the silver part of my die? Hint: it's 25mm on the inside 😁 :

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Had to make a new center spacer/retainer thing too as it was obliterated. The gun lost only 10fps with the leather seal believe it or not. Popped in a new spring of reasonable dimensions and it's spitting out 7gr RWS wadcutters at 630fps. Shoots like a laser! 

Weihrauch put a lot of thought into these guns to make them shoot as good as they do. The piston is featherlight, the shell is thinner and it has a second cocking slot cut into the opposite side. The nose is also aluminum to save weight: 

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A piston this light would be very prone to bounce. One way to get around that is to fit a high-preload spring. The other way, is to open the transfer port to keep peak pressure down. The transfer port here is a healthy 4mm, and around an inch long. That's a lot of dead space and it eliminates bounce/surge perfectly and without the harsh shot of a heavy spring. The downside, is limited power. But that's okay, these things are the smoothest shooting spring gun you'll ever shoot. 

So you may be thinking, "What if the transfer port was 3mm like all the other guns? Would it boost power since the peak compression is higher?"

Well I thought that, so decided to see what would happen. I turned up a brass reducer for the transfer port that was a light tap fit. It will tap in easily, stay in place, but tap right back out with no harm later. Here we go: 

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Well it worked. Boosted power with the synthetic seal by 20fps. But, just as predicted bounce was pronounced and accuracy diminished. So out it came, back to stock and sweet shooting! No harm done, and now we know! 

Anyway, I'm just rambling sitting here with one eye taped shut. Maybe someone finds this interesting. Wear your safety specs kids! 

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The TX tube was rolling around in my drawer. I think it had a bad bellmouth towards the end or something, so it was replaced. I don't own a TX so it got the axe! Works damn perfect for this though. 

I got a piece of steel shot into my eye while I was sharpening a tool bit for the lathe. Funny thing, I had no idea anything was in my eye until about 6 hours later when it started bothering me. The next day I looked in the mirror and saw it sticking out of my eye 😂

Doctor lady snatched it out. Hurts now that there is an open hole there! It'll buff out. Hell I'm basically cross eyed anyway 🤓
 
Thumper,

Nice write-up/pictorial. Thanks for experimenting with that transfer port size and reporting on the results. I've wondered about the factory port size too but lack the wherewithal to try what you did. Appears everything about the HW55 was made right......except I changed my leather piston seals to synthetic. I never could keep a leather seal healthy.
 
Nice job. I have a slightly simpler method to make a seal.. Bore an appropriately sized hole in hardwood with a paddle bit. Press a piece of water soaked leather into it with the right diameter socket. Pressed in with a bench vise, Or large heavy C clamp is what I use. I leave it about a day to dry. When dry I trim off the extra leather with a hacksaw blade while it's still stuck in the wooden block. BTW I make mine with the leather smooth side in. Then I put the cup back onto the socket to then mount the socket in the lathe chuck so I can easily drill a concentric hole with the tailstock.. The slip fit on the socket is just enough to allow a hole to be drilled NP. I make a leather washer to fit the inside of the cup with a little disc of leather cut with a die fashioned from a short tube of the right size to fill the cup. Just press that die into the leather with a piece of hardwood to back it up. Use your vise or a press. Punches out a nice round disc for you. Center drill it. Start soaking the leather in the lubricating oil of your choice. Might take a day. There are ways to speed that up. Old school was to use neatsfoot oil. Then make a thin sheet brass washer to go on top of the assembly held in place with a countersunk screw. Anneal the washer and draw it down with the leather seal assy. in place to get the countersink form into it. Next, harden the washer by heating it red hot and quenching it in water. Yes, brass will harden that way.

Now I assemble the washer onto the piston and load it into the lathe chuck. If oversize enough you can cut the seal gently with a sharp high speed steel bit. Don't hog it you only have that little screw holding it on. Sand the seal until you get a nice easy fit into the chamber. If power is down you might be too tight. Shoot it some to see if it runs in. 

I've made quite a few this way. When working on old BSA I often have to make a new screw as well. The threads on those guns is a proprietary thread. Nothing made today fits, 

I hope this encourages some fellow tinkerers. A thinking man can do it without a lathe......You can buy the right thickness leather very reasonably on eBag. You probably need 8 or 9 ounce leather. I think that's the thickness I usually use.
 
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Got to try out the new seal this morning. Looks like a light wadcutter at 630fps is bad medicine! Especially since my good eye is still about half dilated lol.. 

Hit right under the eye, he stiffened up and fell dead within seconds. I was about 10 yards from the base of a small pine tree he was in, I was in the pine thicket too so he couldn't see me. Dont get that close to a crow very often that's for sure. 
 
Nice job. I have a slightly simpler method to make a seal.. Bore an appropriately sized hole in hardwood with a paddle bit. Press a piece of water soaked leather into it with the right diameter socket. Pressed in with a bench vise, Or large heavy C clamp is what I use. I leave it about a day to dry. When dry I trim off the extra leather with a hacksaw blade while it's still stuck in the wooden block. BTW I make mine with the leather smooth side in. Then I put the cup back onto the socket to then mount the socket in the lathe chuck so I can easily drill a concentric hole with the tailstock.. The slip fit on the socket is just enough to allow a hole to be drilled NP. I make a leather washer to fit the inside of the cup with a little disc of leather cut with a die fashioned from a short tube of the right size to fill the cup. Just press that die into the leather with a piece of hardwood to back it up. Use your vise or a press. Punches out a nice round disc for you. Center drill it. Start soaking the leather in the lubricating oil of your choice. Might take a day. There are ways to speed that up. Old school was to use neatsfoot oil. Then make a thin sheet brass washer to go on top of the assembly held in place with a countersunk screw. Anneal the washer and draw it down with the leather seal assy. in place to get the countersink form into it. Next, harden the washer by heating it red hot and quenching it in water. Yes, brass will harden that way.

Now I assemble the washer onto the piston and load it into the lathe chuck. If oversize enough you can cut the seal gently with a sharp high speed steel bit. Don't hog it you only have that little screw holding it on. Sand the seal until you get a nice easy fit into the chamber. If power is down you might be too tight. Shoot it some to see if it runs in. 

I've made quite a few this way. When working on old BSA I often have to make a new screw as well. The threads on those guns is a proprietary thread. Nothing made today fits, 

I hope this encourages some fellow tinkerers. A thinking man can do it without a lathe......You can buy the right thickness leather very reasonably on eBag. You probably need 8 or 9 ounce leather. I think that's the thickness I usually use.

Awesome info man! A buddy of mine works on a lot of old pump up lanterns and stuff, that's a method he will make great use of, thanks for that! 

I made my center washer out of Delrin this time around. I had some on hand already and it seems to work well. I couldn't tell what the factory thing was as it was turned to dust lol. 

An extra leather washer in the bottom of the cup would probably be a good idea, I'll do that next time. 

Good info bud! 
 
The TX tube was rolling around in my drawer. I think it had a bad bellmouth towards the end or something, so it was replaced. I don't own a TX so it got the axe! Works damn perfect for this though. 

I got a piece of steel shot into my eye while I was sharpening a tool bit for the lathe. Funny thing, I had no idea anything was in my eye until about 6 hours later when it started bothering me. The next day I looked in the mirror and saw it sticking out of my eye 😂

Doctor lady snatched it out. Hurts now that there is an open hole there! It'll buff out. Hell I'm basically cross eyed anyway 🤓

Glad to hear you are okay. Hopefully it doesn't affect your sight. I did laugh out loud though.^^
 










An extra leather washer in the bottom of the cup would probably be a good idea, I'll do that next time. 

Good info bud!

That missing leather washer might be the answer to your missing fps. Increases your headspace volume thereby lowering the effective compression ratio. Installing the washer might also further smooth out the firing behavior

(Edit) You mentioned the delrin washer but my sleepy brain didn't listen. That was one of the first things I thought of this morning after I gave thanks for waking up. 😃

I hope your eye is healed.👍