GTA

All Springer/NP/PCP Air Gun Discussion General => Machine Shop Talk & AG Parts Machining => Show Off Your Air Guns With Mods (SHOW and TELL) => Topic started by: Finn on February 15, 2018, 12:47:13 AM

Title: Reverse enginerding, does it work?
Post by: Finn on February 15, 2018, 12:47:13 AM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on February 15, 2018, 12:51:58 AM
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 !
Title: Re: Reverse enginerding, does it work?
Post by: sixshootertexan on February 16, 2018, 11:45:34 AM
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 (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 (https://www.gatewaytoairguns.org/GTA/index.php?topic=82820.0)
Title: Re: Reverse enginerding, does it work?
Post by: Finn on February 17, 2018, 11:14:02 AM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on February 17, 2018, 11:18:53 AM
excellent work on some rather complex setup and machining !
Title: Re: Reverse enginerding, does it work?
Post by: Finn on February 17, 2018, 11:29:57 AM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 01, 2018, 01:34:53 PM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 01, 2018, 02:02:18 PM
excellent ! this is fascinating , not sure how the rest of the forum is missing this build.
Title: Re: Reverse enginerding, does it work?
Post by: TF89 on March 01, 2018, 03:13:59 PM
Truly sir, you have amazing design and machining skills.
Title: Re: Reverse enginerding, does it work?
Post by: Motorhead on March 01, 2018, 04:05:42 PM
I'm watching ... way beyond my pay grade machine work !!
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 03, 2018, 09:50:13 AM
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 (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.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 04, 2018, 12:13:07 PM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 04, 2018, 12:39:03 PM
reduce spring force holding poppet shut , that's the main regulation involved here, because the hammer force appears super low
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 04, 2018, 01:37:59 PM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 04, 2018, 02:38:27 PM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 04, 2018, 02:39:38 PM
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
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 04, 2018, 07:11:06 PM
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.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 04, 2018, 07:33:59 PM
sounds good , keep pluggin away
Title: Re: Reverse enginerding, does it work?
Post by: AmBraCol on March 04, 2018, 08:32:57 PM
You might be surprised at how many of us are lurking on this thread.  :-) Thanks for sharing your build with us!
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 05, 2018, 11:07:45 AM
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?
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 05, 2018, 02:00:50 PM
You are correct, piston 66 is free riding on the valve stem and it is forced forward before shot by spring 78.

I know these are signs of too large valve, but I also think it should be possible to get better result with the one I have. Valve is clearly shown here http://steyr-sport.com/en/downloads/steyr-air-pistols/parts-lists-with-exploded-views/131-service-info-2017/file (http://steyr-sport.com/en/downloads/steyr-air-pistols/parts-lists-with-exploded-views/131-service-info-2017/file)

I only need 5,5 joules or 4 fpe from this gun and it more than serves the purpose.

Throat diameter is 5 mm and valve body has two 1,5 mm vent holes to feed the piston. Radial air exit holes are 2,5 mm and there is five of those, I suspect that if the throat and radial holes were smaller and vent holes removed altogether, there would be a better chance of success. Piston would still get air from valve stem hole clearance, but it would be bled out in the barrel slower.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 05, 2018, 08:19:20 PM
Made some modifications, now it autoloads with plugged magazine from 85 to 50 bar even when I backed out the mainspring adjusting screw whole five turns, it has a 0.8 mm pitch. Previously it didn't work at all with magazine, only worked if the transfer was sealed shut. I made special test pellets to make testing easier, basically slightly tapered steel pins that will not fit trough completely. Actual pellets do go out of the barrel in a hurry but the mechanism will not cock itself, I hate the idea that maybe I need yet another tighter fit mag. Something is still not quite right but much better than it was.  Any ideas, what should I try/test?
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 05, 2018, 11:50:56 PM
Good improvement, but I would keep the 3.5mm port, and make a valve with 4mm sealing lip out of peek.
Conical valve seal needs much more force to open and you dont need the extra flow from the conical valve seat.
Then you could open up the bleed to the piston a bit to get more air to cycle the gun.

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 06, 2018, 05:34:01 AM
It does now cycle the action even with v1.0 o ring valve, so I think it is not good idea to open the bleed to piston too much. Actually that excess bleed may have been the main problem. As soon as valve is opened and piston is pressurised, it starts braking the hammer and reduces valve lift. If the piston gets air too early in the cycle, the valve lift is too small no matter what the hammer force is. I will turn couple more valve housing blanks to test ideas. I do not have any peek, but it probably works if i use POM for test purposes.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 06, 2018, 07:28:38 PM
Made another valve housing today, or maybe yesterday. It has same specs as 2.0 but I increased the piston size from 7 mm to 8 mm and made new flat valve, had to make the seal diameter 4.5 mm though as 4 mm:s would leave too narrow margin.
Anyway I tested the conical 5 mm valve earlier and max speed was 130 m/s with 0,54 g pellet and the barrel is not that long (183 mm). Still it did not cycle the action with normal pellets.

I only had few minutes of time to test the newest valve and 8 mm piston, and surprisingly it now only lets out only a slight puff sound with blocked magazine and nothing moves but with pellets it was able to shoot and index the magazine. Did not quite reach the sear to stay cocked after each shot but it has never before done the magazine indexing with normal pellets and it is only 1.6 mm more rearward movement from that point to where the sear would catch the hammer again.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 06, 2018, 07:47:59 PM
this is great news!!!!!!!!!!!!!!!!
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 07, 2018, 02:26:41 PM
I will have to tweak some things a little bit, newest valve system does not perform well as something is binding slightly and it requires a lot more force to open the valve than what was expected.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 07, 2018, 07:22:02 PM
This is truly the most confusing thing ever, nothing works as expected.

Case 1. If valve stem is practically air tight to valve body and thus doesn't let much air to the piston, the gun fires pellets with good velocity even with minimal mainspring tension but does not cycle. However autoloading works every time if magazine holes are blocked with tight steel pellets.

Case 2. If valve stem is loose fit to valve body (radial clearance 0.1mm) I need to tighten the mainspring tension a lot to get the same velocity and if magazine is now blocked the gun will go full auto for a second or less but does not stay cocked. If the gun is fired with no magazine or empty magazine, the slide cycles almost all the way back but does not stay cocked after shot.

Should I make that stem hole little bit bigger and just hope it will work, because if it doesn't I'll have to turn another valve body.

There must be some small detail that I am missing here, if only there was someone willing to give me their Steyr LP50 to study, this would be solved in a minute.  I refuse to believe there is a part in that gun that I couldn't make.
Title: Re: Reverse enginerding, does it work?
Post by: cobalt327 on March 07, 2018, 07:46:10 PM
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 (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 (https://www.gatewaytoairguns.org/GTA/index.php?topic=82820.0)
Hope the photos will show up as attachments...
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 07, 2018, 11:54:38 PM
This is truly the most confusing thing ever, nothing works as expected.

Case 1. If valve stem is practically air tight to valve body and thus doesn't let much air to the piston, the gun fires pellets with good velocity even with minimal mainspring tension but does not cycle. However autoloading works every time if magazine holes are blocked with tight steel pellets.

Case 2. If valve stem is loose fit to valve body (radial clearance 0.1mm) I need to tighten the mainspring tension a lot to get the same velocity and if magazine is now blocked the gun will go full auto for a second or less but does not stay cocked. If the gun is fired with no magazine or empty magazine, the slide cycles almost all the way back but does not stay cocked after shot.

Should I make that stem hole little bit bigger and just hope it will work, because if it doesn't I'll have to turn another valve body.

What I would make is machine a small flat on the valve stem, you can test with that and dont need to make another frame part.

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 08, 2018, 05:16:23 AM
I will do the flat first and if the theory is proven I will maybe then drill the valve body. Stem could also have tapered section to change the airflow in relation to valve lift but first test would be with flat.

I could also just change the stem itself because it is separate part from valve head. Stem is threaded in and it expands and crimps the o ring in. I might have even saved the nc program for stem but it is better to write new parametric program if different sizes are needed.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 08, 2018, 05:45:29 AM
I just noticed something important while watching a video https://www.youtube.com/watch?v=lT8h3_2eCrc (https://www.youtube.com/watch?v=lT8h3_2eCrc) around 0:30 seconds mark you can see where the sear catches the bolt. I definitely messed up somewhere because my sear catches very late in the cycle and it might just be that the hammer rebounds hard from the rubber buffer before the sear has time to flip up. Evidence supports this because if the transfer is blocked, the piston has more pressure at the end of the cycle to counter the rebound and sear has time to flip up to locked position.  See attachment, could this be it, new sear and we are done.

Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 08, 2018, 09:19:56 AM
That could be the reason for full auto. That is pretty formidable difference in cocking distance.
Changing the valve stem to conical would be interesting to see how it effects the cycle.

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 08, 2018, 11:28:52 AM
Surely I will be testing every combination once the sear is remade or modified. There is one added benefit with moving the sear lip forward, it increases the leverage and hammer will start accelerating much easier because it has to push against sear spring and disconnector when gun is fired.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 09, 2018, 05:49:30 AM
Much time could have been saved if I had been more observant while designing the gun, I watched everything available on youtube many times and still didn't care to check the sear position.

It now works as it should, I was able to rapid fire at least 6 full magazines of crosman destroyers before I took the gun apart for inspection.
Test pressure was 65 bar, if higher pressure is required a new tighter valve stem must be made to reduce hammer brake effect.
Only thing I changed to make it work was the sear, hook was moved 2mm forwards.

There are still things to do make it absolutely reliable but at least now I know every aspect of the clockwork and what needs to be adjusted.

I will leave the valve assembly for now and start making the following parts

-RH cocking lever and safety lever
-regulator and air reservoir
. barrel shroud
- Target sights
- anatomic form grip
-trigger shoe
-regulator tester
-spare magazine
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 09, 2018, 09:04:29 AM
THIS IS AWESOME NEWS!  congrats/.... I cannot imagine how many hours  it took to get this far ..
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 09, 2018, 10:13:21 AM
It is around 200 hours give or take plus the cad design and web research. I had to make many tools that are not shown here and probably need to make more. 8 hour day job limits the speed but I do all the machining at night anyways so there is no one bothering me with anything else.
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 09, 2018, 06:35:47 PM
Nice going man, really nice!
It is truly interesting to see your work, its always so different.
Makes me feel like a hack, I'm just tinkering with stuff.

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Hobbyman2007 on March 09, 2018, 09:34:38 PM
Congrats on getting this fine pistol figured out and working . Your attention to detail is astonishing great to see it all worked out.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 13, 2018, 09:30:11 PM
Nice going man, really nice!
It is truly interesting to see your work, its always so different.
Makes me feel like a hack, I'm just tinkering with stuff.

Marko

Don't feel bad, your projects have manly man qualities and at least you will be an actual engineer and that is something  ;)


Grip work has started, it is the most difficult part to get right. I started with machining the shape of my hand in some random block of wood, cutter is 12 mm ball shaped made of tool steel. I didn't machine the external shape, it will be done with hacksaws and files and whatnot when the gun is fitted in the grip. I'm trying to get that grip as high as possible and in a large angle where my wrist is locked downwards it will help to get a proper sight picture quickly. Took down largest of sticks and ridges with sandpaper, it fits in my hand and doesn't hurt like h***.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 13, 2018, 09:43:32 PM
Pistol shrouds shouldn't be too much work but this one was, I started with 30 mm bar stock, most of it is gone now. Had to use every trick in the book since it has t-grooves, round bottom slots in a strange angle, serrations, million holes, angled ports, long holes, internal & external radius and all that stuff.
Guns internal parts are mostly removed, trigger guard chamfers had to be filed in there, lots of alu powder. Black part on top is the first rear sight part, it contains the ramp for elev. adjustment and moves back and forth to change sight radius.
Finally a comparison between my second homemade target pistol and this one, I do believe that the grip material for the newest is that same wood.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 13, 2018, 09:43:55 PM
looks awesome, and from you I'm not surprised !!   ;D
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 14, 2018, 02:15:41 AM
Oh my that is going to be one fine looking pistol. Time and patience to build it, outstanding!
Could I do it, yes and no. I dont have enough time.  ::)
I'm more of a funktion over beauty kind of guy.
Albert if you ever want to try and shoot the 20mm, it can be arranged.  ;)

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 14, 2018, 02:50:18 AM
what model is the bottom one ?>
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 14, 2018, 07:08:58 AM
I don't have a name for it but it is basically a mix of Walther LP line of pistols and my own ideas built back in 2013 if my memory serves me right.

Oh my that is going to be one fine looking pistol. Time and patience to build it, outstanding!
Could I do it, yes and no. I dont have enough time.  ::)
I'm more of a funktion over beauty kind of guy.
Albert if you ever want to try and shoot the 20mm, it can be arranged.  ;)

Marko
Form comes from the fact that I am building a 1:1 scale model of a gun, my own designs are usually a bit more utilitarian.
Shooting the 20 mm beast would be once in a lifetime experience (I mean who wouldn't like a good beating ;D). If I start weight lifting today, I may be able to handle it when the time comes.  I will probably never build anything like that, can't even think of a range nearby where I could actually shoot it.
Title: Re: Reverse enginerding, does it work?
Post by: AmBraCol on March 14, 2018, 11:12:31 AM
I like that grip.  Need something similar for my IZH-46M.  :-D  Thanks for sharing this build with us!
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 16, 2018, 06:26:27 AM
Worked the grip yesterday, it not worthy oil like a sponge.
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 16, 2018, 06:35:02 AM
That is really beautiful, nice work man!
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 16, 2018, 08:46:51 AM
Worked the grip yesterday, it not worthy oil like a sponge.

this is outrageous lol..the factory will be calling you for woodcarving  tips
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 16, 2018, 11:20:16 AM
Just saw what I posted, this is an outrage, I wasn't politically correct when using the s*ck term to describe the oil absorbing capacity of the wood. Normal words should not be turned into hebrew by forum censorship software, I hope that people could behave so that automatic censorship could be omitted, but that never happens when one can anonymously express thoughts.

Enough with the rant, time to check if the gun still shoots with the grip on. If it does I will test a couple different diameter valve stems I have and start designing the regulator and air tube.

Grip will receive a new coat of oil whenever the last one has been absorbed, it has two coats in the photos.  Might just be the best grip I ever made, it's not like holding a pistolgrip it's more like putting your hand in lukewarm water.
Title: Re: Reverse enginerding, does it work?
Post by: farmerjoe99 on March 16, 2018, 01:37:34 PM
Truly amazing work Albert!! Thank you for sharing your builds, they are a joy to follow and inspiring as well.

Regards,
Joe
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 16, 2018, 02:57:01 PM
hows the semi auto function now ?
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 16, 2018, 04:33:28 PM
Seems that I have lost the original sear spring but it did work with poorly fitting spring. In fact it was difficult to adjust the mechanism in such way that it wouldn't work, fired 40 pellets and it worked well if the pressure was kept between 65-80 bar. I feel it works better and has more velocity with tight valve stem (0.025 mm radial clearance). Next I would try to find the best length for valve stem, it will be simple if I make a piston with small adjustment screw, no need to cut the valve. However it is best to do those things last as the hammer will be heavier when right hand cocking lever is done.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 16, 2018, 10:48:45 PM
The day is over, it currently 3:40 am and I have been making parts six hours straight with no breaks.
Parts that I made:
- Regulator housing
- 3 sets of regulator springs (0.4 mm, 0,5 mm and 0,6 mm)
- Regulator piston and seat
- Retaining part for piston seat
- Part that attaches the reg to gun.

Now it is time to relax and crack open a beer and watch some pbs space time, tomorrow is the air tube day and maybe I get to shoot the pistol with mock up sights on Sunday. Some 500 crosman destroyers have been destroyed while testing the action, really they are almost good enough for that.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 18, 2018, 11:31:36 AM
Almost there, now that I can actually shoot the gun I am starting to see and feel what I have made. It is just incredible experience, trigger is absolutely match grade, light 200 gram pull with short clean reset and the gun points itself to the target with no effort.
  Air tube is steel and sets the CG nicely. Shot the gun with 65 bar fill, as I forgot to make the test connector to check reg. output so I have no idea what the set pressure is but it is over 70 bar. Shot a couple of 5 shot groups from 5 meters away (to save the furniture) without sights as fast as the finger moves and they were all about 1 inch.  Also had a couple of goofs, forgot to tighten the barrel setscrews and to my surprise it shot fine even when the barrel had slid 4mm forwards.
Also had a bad idea about using M3 screw on the shroud front screw hole as temporary front sight. I
t would have worked but as I shot the screw turned further in and soon the pellets started hitting windows 1 meter away from target. Had to cut that screw off with dremel diamond burr because it was bent 90 degrees and pointing outwards from the muzzle, luckily no damage was done to the shroud.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 18, 2018, 11:49:48 AM
amazing... awesome job
Title: Re: Reverse enginerding, does it work?
Post by: MJP on March 19, 2018, 12:56:18 AM
That is truly amazing, something that no other can say at the range. "I just wanted this pistol so bad that I decided to make it"  ;)

Marko
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 19, 2018, 08:15:13 PM
I have thought about that, but nobody at the indoor shooting range where I go has any interest in what guns someone has, neither are they very knowledgeable about air gun tech in general. So I don't tell anyone I made the gun unless they ask, you guys are the only people getting to see this gun being built and have all this in depth information about it.

Wasted half a tin of pellets today, it didn't take too long. I made temporary rear sight from sheet metal, M3 setscrew serves as front post. Accuracy is good enough I think, it is likely to improve when I get those sights done and proper crown on the barrel. Tested pellets were RWS R10, RWS meisterkugeln LP, Exact 8,44gr and Crosman domed.  Regulator was set at 60 bar, used 7 0,4mm bellevilles, chrono was set up just front of the target at 9 meters. Only pellet that gave readings was exact 8,44 gr and it clocked in at 110 m/s at the target. Velocities were really stable over 20 shot test series, it was always 110 or 109 m/s, I should mention that I took my time shooting as the chrono is picky about shot placement and larger velocity spread is expected when rapid firing.
 Pressure must be changed if more speed is required, if mainspring adj. screw is out of setting range by 1/2 turn, auto loading doesn't work anymore. There is a range of one complete turn (0,8 mm pitch)where everything works perfectly, that is only +-0.4 mm more or less tension on the spring. Heavier pellets are more reliable, JSB exacts worked every time no matter how fast the trigger was pulled, Crosman domed on the other hand barely worked at all, they almost fall through the mag. RWS pellets all worked but they must be pushed into magazine properly or the skirts will rub in the mag housing.




 More testing tomorrow, I want to check how the mainspring screw effects velocity vs auto function. Accuracy will also be tested more, it might be a good idea to make a removable rail for red dot sight while iron sights are WIP, really want to take my time and make those sights perfect.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 25, 2018, 07:56:21 PM
Made more parts, rear sight is almost done. Air stripper is also done, don't have any data if that changed anything else than looks of the muzzle area. Upped the regulator pressure and spring tension, V0 is now 130 m/s and I am astonished by the accuracy of this thing, took 5 shots (rested) in approx two seconds and got 7 mm hole in the paper 9,5 meters away!  Only the first shot after refill hits low, I guess something has to be done with the regulator to fix that, need to think about it.
 I used reflex sight for accuracy testing, it would be difficult to use open sights shooting from tabletop where the eye is closer to the gun, grip also is only good for offhand shooting.
Title: Re: Reverse enginerding, does it work?
Post by: Finn on March 25, 2018, 08:23:07 PM
Reflex attached to the shroud rail, really horrible position for offhand, works ok for benchrest shooting. Had to install some filters inside the sight to get rid of light streaks and reduce the dot size, now it is really small on the lowest setting and light artifacts are gone.
Title: Re: Reverse enginerding, does it work?
Post by: Rob M on March 25, 2018, 10:40:59 PM
awesome..whats the finish on the shroud and trigger area