Reverse enginerding, does it work?

[Finn]

I decided to share with you my reverse engineering adventure. Since I first saw LP-50 pistol, I've really wanted to own one and train some rapid fire shooting. Anyway to make it interesting, instead of buying it, I want to make it myself. I started with studying the spare parts catalog and few photos as my only reference and constructed a cad model based on those. Heres a few photos showing a current progress, share your thoughts, especially if you think I got it wrong. I haven't modeled every part just yet but enough to start with, I will use my own regulator and air tube design so no need to model those again. Tricky part is the magazine timing which is critical when the striker moves as little as it does.

[Rob M]

this is brilliant ! I always thought about  buying a gun , then copying all the action parts in the shop , then selling the factory gun to fund the rest of the project ... Making the cad profile with limited knowledge of the part specs  is very impressive .. subscribed !

[sixshootertexan]

Looking good.
I modeled my .308 after the AA S510 TC and then made it in my design.

https://www.pyramydair.com/product/air-arms-s510-tc-pcp-air-rifle?m=2386

Don't know if the pics will show up due to Photobucket's ransom fee's.

https://www.gatewaytoairguns.org/GTA/index.php?topic=82820.0

[Finn]

Unfortunately no, I cant see the pictures.
 Made some progress yesterday, frame machining is completed minus the top radius and trigger guard chamfering. Started making the magazine housing, and the next part would be the magazine and barrel fitting. More could have been made but my hydraulic press refused to cooperate at first when broaching the square magazine hole. I think after the barrel fitting I would need the valve assembly made to check if it works and holds air.

[Rob M]

excellent work on some rather complex setup and machining !

[Finn]

Thanks, those valve threads were almost troublesome to do with lathe, deep and narrow hole and the chip evacuation is bad. Forgot to mention that I pre checked if the frame will take the full air pressure without breaking. It seems to take 300 bar fine and still leaves a nice factor of safety even if I accidentally used 6063 alloy. That aluminium stock was promised to be 6082 so it is certainly strong enough when considering this will be a 200 bar gun.

[Finn]

Some parts have been made, valve holds air from 1 bar up to 100 and magazine works exactly as it should. I had to make a new hardened mag from tool steel because the aluminium I had used was too soft for the purpose and it is a difficult part to make so it better last forever. Valve parts are all stainless steel, hammer and other moving steel parts are 42CrMo4. That chunk of aluminium where the air tube would normally go, is just a probe connect point for testing.  Still needs at least five parts before I can test if it shoots and autoloads.

[Rob M]

excellent ! this is fascinating , not sure how the rest of the forum is missing this build.

[TF89]

Truly sir, you have amazing design and machining skills.

[Motorhead]

I'm watching ... way beyond my pay grade machine work !!

[Finn]

So there is someone actually watching, nice. I'm now only couple parts away from testing if this actually works.
 If you look here http://www.benke-sport.de/epages/es948641.sf/de_DE/?ObjectPath=/Shops/es948641/Products/%22ET%20LP50%22
  parts in question are 76, 70 and 71. I already made 31, 32 and 33, just havent taken photos yet.


Link should show exploded view, if not just update the page and it appears.

[Finn]

Now it is turning into a difficult puzzle, there is a problem with valve opening force. Gun does shoot but it only shot 60 m/s when the mainspring adjuster was  bottomed and no autoloading.
 Question is, what should I do to it ? valve is 6mm diameter where it seals and mainspring is very hard but still the gun does not have much power. Power goes up when pressure goes below 55 bar and peaks around 50.
 Trigger mechanics work and I can get the mechanism to autoload if barrel is blocked and lighter hammer spring is used but it is too light to shoot pellet out of the barrel.  I have tested plastic valves and the one with rubber seal (similar to original Steyr part) and it doesn't make much difference either. Blowback piston diameter is currently 7 mm, that was taken from steyr parts catalogue where it states that the piston o ring is 4x1,5 mm.
First photo shows the mechanism cocked and second one fired.

If you like puzzles and even if you don't, YOU maybe able to help me to solve this one. Look at the part diagram in the previous post and attachments below, and share your thoughts, what parts I got wrong.

[Rob M]

reduce spring force holding poppet shut , that's the main regulation involved here, because the hammer force appears super low

[Finn]

What you mean by regulation? gun is attached to a pressure regulated feed line for testing.
I already tried to lighten the valve spring to the point where it was difficult to build up initial pressure, but that was before I made o ring sealed valve, so maybe need to try again. Also there is some friction in the movement of cocking lever that also indexes the magazine, maybe some polishing is needed in couple places. It is not immediately obvious from those spare parts catalogs, but I think my valve stem may be too long. By shortening the stem I could gain some hammer travel and little more power maybe. It would not have much effect on how the blowback piston works but I would have to try it to know better.

[Rob M]

self regulation.. ( not literally a regulator .)

Ok , you have a power struggle here.. let me simplify.. The rearward force of the blowback has to overcome the hammer force , so the hammer force cannot be excessive.. SO now we have mediocre hammer strike,.. that same mediocre power strike not only needs to break the back force of the air , but also the force of the spring holding the poppet shut.. So , since you cant change the force of the blowback system which is dictated by math , You can weaken or shorten the poppet spring and let the system breathe.. Duration of the valve is often more important than porting of the valve when working in tight confined travel spaces.

[Rob M]

agreed 100 % , SHORTENING THE valve stem on the poppet will also have the same effect on duration of the valve .. its actually one of my favorite mods when done in moderation ( a few MM 's

[Finn]

Okay, I now understand what you meant when you said regulation, that is important. I was thinking the same exact thing but thought that you might be thinking something else, I need to hone my questions and interpretations.
Anyway I did not shorten the valve stem but drilled the bb-piston hole 1mm deeper because that's the one thing I couldn't derive from part diagrams.
Steyr website had some service data pdf that had a photo of the valve on a millimeter scale, so I think at least my valve is very close to original dims.
Would be extra useful to have a photo of original valve housing, but it doesn't seem to exist.

However I tested again with deeper holed piston and oring valve and wimpiest return spring that allowed filling. It looks like things improved quite a bit from previous test session. I plugged the barrel and started from 60 bar pressure. Pulling the trigger made very muffled "puff" sound but the mechanism was able to autoload pretty much every single time down to 30 bar.
Below 30 bar the gun vents all the air. This tells me that the main spring needs roughly 11.5 kilograms or 115N of force at most to be pushed all the way back since the piston diameter is 7 mm. It's not exact because that pressure is reservoir pressure and air expands to fill all that space after the valve is closed.
With magazine and pellets there still is not enough back pressure to get autoloading, but I think the magazine indexed couple of times so the slide must have moved rearwards a little bit.  But yes, what next, I feel like the main spring should be stout enough as my finger has serrations instead of fingerprints from cocking the action all day.

[Rob M]

sounds good , keep pluggin away

[AmBraCol]

You might be surprised at how many of us are lurking on this thread.  :-) Thanks for sharing your build with us!

[MJP]

Holly cow how did I miss this one, too much to do at the university at the moment.
Nice work man, you have much more time on your hands than I do.
You need a smaller valve, did you say it was 6mm? How many Joules is the target?

Marko

Part 66 is acting like an air piston and eating all of your hammer energy. If I looked at the right part.
One more editing, is the valve attached to the piston? I think the piston should free ride with the hammer,
Adding its mass to the hammer strike, should it be back against the hammer after previous shot?