AirGunTech: Re Engineering Spring Powered Air Rifles for smoothness, consistency, and to better suit UK power levels.

2nd update on the HW80/LGV build.

Piston arrived..spent an hour altering the main sear on the Rekord trigger and its shooting….extremely well !! πŸ™‚

I will update with pics of the trigger sear modification and the modification needed on the cocking shoe…the piston is pretty much a drop in job…bang on 80mm stroke also πŸ˜‰ I will no doubt polish the sear modification and re harden the sear.

Some news on the Walther LGV piston:

The piston tube is machined from a thick walled tube, the rear skirt is hardened and the piston nose end is internally threaded. The Piston nose is externally threaded and screws into the piston tube. The piston nose is drilled and tapped for the piston rod to screw in. The front bearing sits on a shoulder just behind the piston seal…and lastly the ** piston seal is a direct copy of a Weihrauch** unit (how it fits/snaps on and yes you can fit a HW or after market HW seal to the LGV piston). I also have a feeling this piston will be a drop in modification for the AA TX200, not sure what stroke it would give in the TX however, will experiment at a later date.

 

** now found Walther were actually the first to use the parachute design synthetic seal of this design and HW looked to have copied Walther…this dates back to around the time of the first gen LG55 and LGV’s.**

 

 

 

 

 

 

 

 

Small update on the HW80 build…..adding the compression cylinder sleeve

Work has started on the 80 build now, decided to start with the compression cylinder while waiting for parts.

The compression cylinder length is dictated be the distance from the breech to the cocking shoe aperture machined into the main cylinder…this happens to be 95.2mm on the gun I have here, the chosen stroke will be 80mm so I have around 15mm behind the nose of the piston when the gun is cocked for me to add fixings so the new sleeve is held tight against the face of the breech.

As mentioned earlier I chose to sleeve down to 25mm, the reason for this was so either the TX200 or LGV piston could be used, this would save a ton of machining (as long as the pistons can be adapted easily)

So…easy first cut is machine a length of tube down to 95.2mm, I actually went for 95.1mm to gain a midges of clearance.

Next step is to machining an O ring groove. I chose to use 30mm OD 2mm cross section O ring, groove was machined to give 0.25mm crush on the O ring, from the front face and from the outer cylinder …this was to ensure a good seal (I hope ;))

 

The actual machine marks have been polished out now, this is important for the O ring to give a consistent seal, I polished to 320grit but forgot to take a pic…you get the idea and reasons why though ;). Following pic shows the O ring installed.

 

 

 

 

 

 

 

 

 

 

 

Moving on, next was machine in the fixings for the sleeve…with having 14mm available I went for the roughly accurate approach, there is plenty of space to get these in so just marked the positions with a sharpy marker and drilled to 3.2mm…

 

The 2 holes are 13mm away from centre.

 

next step is de burr, then with the O ring removed from the sleeve insert the sleeve into the action. NOW…after strugglingΒ  with the method I used I realised it would be easier to add a 3rd hole to the sleeve around 2mm from the back edge so a hook can be inserted to withdraw the sleeve..2mm dia or so would be all thats needed and a bent TIG rod could be used to withdraw the sleeve. This 3rd hole obviously needs to be added to the sleeve before you insert it for the next stage which is marking the position for the fixing holes from the 2 holes already drilled into the action. Also note I added the old piston back into the action backwards and then screwed the trigger block so some pressure was applied to the sleeve to hold it in position while the additional fixing holes were drilled.

 

Now…once drilled, remove the sleeve tap the2 holes in the action M4, then again deburr the inside of the action, tap the sleeve for the 2 fixings M4 and again deburr the outer and the inner. Its a long winded process, you have to ensure the sleeve slides into the action smoothly with no burrs, this is also important for the O ring as any damage will lead to a leak at the breech face.

With the sleeve drilled and tapped and the action drilled and tapped and all de burred add the O ring.

 

Now we have 1 last job on the action before inserting the sleeve and loctiting its fixings…the transfer port.

 

I have no pics of this, but will explain why the transfer port diameter has been altered. Final stroke is hoped to land bang on 80mm, this gives a piston swept volume of 39.28CC

The HW80 transfer port is 11mm long, I want a final static compression ratio of 350:1 or as close as possible, so reverse calculation gives 3.6mm for the transfer port diameter needed.

Static compression ratio = Piston swept volume / transfer port volume.

so transfer port volume =Β  Piston swept volume / static compression ratio

 

Once you know the transfer port volume you can reverse the calculation for volume of a cylinder to give the radius of the transfer port which you double for the diameter.

Pi * (r squared) * h = VΒ  so

V/h*Pi= r squared, so we need to hit the square root to get r then double it for the diameter.

Use as many decimal places as you can for accuracy…reverse checking though (otherwise known as the trial and error calculation method)is always good so…

Piston swept volume = 39.28571428571425CC

transfer swept volume with 3.6mm diameter and 11mm height = 0.11201142857142848CC

39.28571428571425/ 0.11201142857142848 = 350.729517

So pretty close to 350:1 πŸ˜‰

 

So…the transfer port is drilled out carefully to 3.6mm, then lightly polished with a bootlace soaked in Autosol polish before the action is washed out with degreaser and dried. Then last job for this update is grease the sleeve and O ring and press the sleeve into the action, compressing it while 2 x 4mm long M4 grub screws are blue loctited into place to hold the sleeve hard and tight against the inner breech face. The grub screws need to finish just below the inner surface of the inner sleeve so they do NOT foul on the piston seal when inserted πŸ˜‰

 

This is pretty much where I am at right now, waiting for the piston to arrive and the new style cocking shoe that was shown in stock but was obviously not due to the week+ lead time for delivery gggrrrrrrrrr!!!

I have pressure tested the action for 30mins by blocking the transfer port from the inside of the action and pressing a hw77 piston into the sleeve…it held pressure well so im looking forward to the next stage of the build

 

 

 

 

 

 

 

 

 

 

not updated for a while….does not mean tinkering has not been done and knowledge gained however !!! ;-)

Its been a good few weeks without an update, quite a few PCP projects have been on the bench and I will bring them to the blog when I can…for now however I have something new…more of a challenge.

I reported that Walther were bringing a new springer to the market, the LGV2012, it arrived and while being seriously well engineered rifles the final finish of the gun is not what I personally would pay near Β£500 for so for now im giving the LGV a miss..however that will not stop me having a go at creating my own.

During the past few weeks a few projects with different rifles have allowed me to explore more of the science of what makes a springer tick, a fellow tuner who frequents a few of the UK forums helped with a HW 55 experiment and initially decided he would have a go at a home brew LGV based on a HW35. He has helped steer my thoughts and answered those questions that sometimes you just can not get your head around…if you see posts by T 20 on any of the airgun forums make sure to read what he has to say….he knows a thing or two about springers πŸ˜‰

So…back to the new project…It has to be like the new LGV, not a direct copy but like it, so I searched for a base rifle that would take the modifications and could be picked up cheaply second hand.

Bring on the HW80.

Now the specs for the LGV are 25mm piston, 88mm stroke, piston runs in a sleeve but has a skirt that is larger (diameter) and runs on bearings…bit like the AirArms TX200 piston. The cocking lever slides on a sprung bearing and the piston rotates…

Can I do all this with a HW80?

Now venom /V-mach offered a sleeved conversion for the HW80, I know of it but have never seen one so what I will show is my take…. how I would do it. My plan is to have a rotating piston, utilise the new cocking shoe HW have just phased in but add bearings to keep its operation smooth. The stroke will be set to around 80mm, this will give a swept volume of 39CC…this gun will be re engineered for UK sub 12FPE use only.

During the tune work on a HW55 I was able to experiment with stroke and swept volume as well as transfer port tuning, there looks to be a magic static compression ratio that must not be ignored, set below it and the firing cycle can get slammy with light weight pellets, set way below it and the gun will suffer from a smashed piston. I will explain more as the build unfolds…It also probably deserves a thorough write up also as there is quite a lot involved.

There is one ironic part of the build, the piston I have chosen to use is the actual Walther LGV piston, its ordered and hopefully will be with me in a few days, i can then decide what machining is needed to get the 80mm stroke and convert the piston to run a Vortek vac25 seal. Of course it may not even lend itself to the build yet…im hopeful it will obviously. The one hurdle i do have some concerns about is the trigger sear engagement on the piston, the LGV piston is very different to the HW piston so there may be some alterations needed.

The gun is already to hand, its an early .22 80 that was bought for Β£120, its been painted, it has a chopped .22 barrel but it has a nice Mk1 right hand HW80 stock and its transfer port is untouched. The barrel will be swapped for a 410mm .177 barrel (which is ordered) the original barrel will be cleaned up and re blued and kept with the rifle to keep its history. A barrel weight will be added, 20mm OD around 180 to 200mm long, this will be blued steel. The plan for the stock is to refinish it, stain it back to walnut BUT stipple the pistol grip and belly of the for end then blacken them much like the HW98.

The piston sleeve is also to hand, 30mm OD 2.5mm wall (BS3602Part1 CF5360 NBK) CDS tube, it slides into the action beautifully and its machined accurately on the ID and looks to be perfect for the VAC25 seal I want to use.

The next update for this build will have the new barrel and I hope the piston and cocking shoe all to hand..the build will then officially commence.

 

More soon πŸ˜‰

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Helping out a mate with a seriously boingy HW80!

Shooting at the local club a few weeks back could not help but notice a mates HW80 was seriously boingy/twangy, in fact you could hear the spring twanging from 10 feet away!…so it was time to help.

The HW80 has a stock stroke of 80mm, hence its name, bore is 30mm for a swept volume of 56.6CC, this places it squarely in the magnum springer range designed for FAC use, so not really very good for sub 12FPE. I have tried everything possible to get the 80 shooting nice with a stock stroke, its always to lazy, short stiff springs, long weak springs..tried them all, so its time to short stroke.

With the gun being around 1 year old the compression cylinder is not honed true, this had me worried somewhat..however there was no need to worry. The internal cylinder was near on mirror finished and really quite true so the conversion to O ring seal was a go, stroke reduction to 55mm for 39CC swept volume (rifle is a .22)

The only other modification was to increase the transfer port from 3.2mm to 3.6mm, this allows the best from the 39CC and reduces felt surge, The spring is shortened to the length used for the HW35 with a new top hat machined from Acetal…power was 11.2FPE with Falcon 13.4Gr pellets, seriously easy to shoot with the only down side being the cocking arm only starts to push the piston back after the barrel has already travelled 30deg of its cocking cycle…not much of an issue for me but for some it may sway them against the modification.

Some pics of the piston just before installation.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

As you can see the piston is quite a bit longer than standard, 3 button bearings are added to the piston extension and a rear bearing added to the skirt of the piston…end result is no metal to metal contact, really very smooth cocking and firing cycle, dull thud, no hold sensitivity at all, fast lock time and very accurate. In reality this is much akin to transforming the HW80 into a HW35….still if it makes it easier to shoot and more pleasurable to shoot…why not! πŸ˜‰

 

 

 

 

 

 

 

 

As mentioned a HW35 spring is what you need with this conversion, I would say the HW spring would be better than a bought kit spring as they usually are shorter and stiffer…and we still need some preload to counter piston bounce.

Now…My own HW80 is short stroked also although by 20mm not 25mm, my rifle having 42.4CC swept volume, i fitted a lazier spring to my gun and utilised an early HW90 barrel which has a set back cocking lever pivot point. Whether this feels better I will have to test when i get a chance to shoot my rifle against this gun here. Overall though a really nice end result with both conversions, safely below 12FPE and little swept volume to allow for power creep (especially on the 39CC piston) Ultimately both rifles feel like a full tuned hw95 to shoot…really quite special.

 

 

 

TX200 Mk3 quick short stroke conversion to conver the mk3 to the same stroke of the mk1

Air Arms originally designed the TX200 to very closely copy the bore / stroke / swept volume of the early 25mm piston HW77’s, then in a move i can only think was sales driven (USA market) they decided to up the power capability of the TX. This meant for UK use the guns were set up with a softer spring and heavy piston weight/tophat..not idea at all!!

I’m not going to go into mega detail on this conversion, I swapped a sweet HW98 for a TX200 purely to experiment and see if I could get the TX as nice as the HW97…and i believe i have managed it. To start I short stroked the TX down to 39CC with -18mm stroke using a new alu piston nose (so same as the 25mm piston 77’s)…this worked great except the bear trap often would not engage correctly. With this and being short on time i decided to push the stroke to -14mm for just a midges over 41CC swept volume. I may in the future remove the bear trap and push the stroke back again to 39CC (81mm so -18mm) but for now this worked quite well.

Pics show the alu piston nose, i ended up using a Vortek 25mm HW77 piston seal. Initially the conversion used an O ring, the problem i found was it just felt to fast, which sounds very strange…moving to the HW77 25mm seal and noting the seal is cupped so in reality the stroke was increased by 1mm or so it felt much nicer to shoot.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Piston nose is attached with the 3 grub screws and loctite, it is removable if needed.

For UK sub12FPE use you can copy what I did here or find a mk1/2 piston which has 14mm less stroke..OR fit a new piston rod with +14mm length, i went the piston nose route as its much easier. This transformed a sluggish shot cycle to something very similar to that of the HW97…maybe a tad quicker. You think your mk3 shoots nice? I bet you would say its nicer once this conversion is done, especially if you have ever shot a nicely tuned HW77 or 97.

 

 

 

 

Diana 52 short stroke for sub12FPE use

Here in the UK RUAG are discounting down the Diana 52k’s, they are only available in .22 which is kind of a bummer as i really wanted a .177 but i decided to jump in and have a play with one. Now…. only .22, i think i know the reason why πŸ˜‰

The gun is basically the German spec carbine…2mm transfer port an all, so it looks like the .22’s just do not sell in Germany so to push stock out they pushed it to the UK. Now..the downside is these guns come with the full power spring BUT are restricted down with the 2mm port restrictor, this makes them bordering on horridΒ  to shoot! All is not lost though πŸ˜‰

Having already tuned my 280k and swapped out the spring I figured I would take a look at the difference between the Diana 52 magnum spring as fitted with the 2mm port restrictor…

As you can see the 280K spring is a full 30mm shorter, this will come in handy when the modifications are finished. The spring that came with the 52 with the piston in stock form with stock stroke would not be a wise thing to run without an FAC here in the UK so I decided to stroke the 52 down. Standard the 52 with T06 trigger has 100mm stroke 28mm Bore for 61.6CC swept volume, way way to much for sub12FPE and just fitting a weaker spring with no transfer port restrictor would make for a very lazy shot cycle…so drastic measures are needed πŸ˜‰

This is a new piston head I machined up from Alu , it reduces the stroke by 38mm. Note i added button bearings to this also as well as the use of an O ring over the oem piston seal.

To give you all a better idea here is the piston head fitted…I also added a full sleeve and rear bearing the same as i did with the 280k.

This makes for quite a long piston…not to worry thought the 52 is a long rifle and copes with this quite well.
I actually did a slight modification to the piston nose to accommodate the new alu nose i added, here is some detail if you wish to copy what i did. This just gives a little more meat for the grub screws to bite into.

End result with 36mm less stroke is a swept volume of 38CC or so, the transfer port restrictor is removed to allow the piston to breath through the 4mm transfer port..the result is a dull thud of a shot cycle and a very fast lock time, much much different to the way it shot before.

I will update with some pics of the full gun, this was supposed to be just an engineering exercise with the gun being sold on, however it shoots so nice now i just can’t let it go πŸ˜‰

Blackpool Air Rifles here in the UK look to be the cheapest place for the stubby Diana52, shop around though if you want one, remember its a magnum springer detuned so to get it sweet you will need to work on it. If you go the full money and short stroke it like mine here aim for around 38 to 40CC swept volume. I actually made a new top hat and used the 280K spring for the conversion, it still needed 2 full coils removing which leads me to think I could have pushed down to close on 37CC for sub12pfe in .22 with this super efficient springer. Its really quite sweet to shoot…and seriously worth not over looking.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Some interesting reading for the airgun enthusiast

Take a read, follow the links within this patent filing also…some interesting stuff looks to have now expired the 20 year rule.

 

http://www.freepatentsonline.com/5570676.html

Looks like Walther will have the best springer award this year….bring on the 2012LGV

Found a link to a newly uploaded PDF/Brochure for the Walther 2012LGV, for those a little older they may remember the old LGV target rifle which had an awesome barrel lock, well this new version is a high power sporter; has the same barrel lock and a whole lot more…check the PDF

http://www.ste-sidam.fr/home/8.1008_Walther%20LGV%20en.pdf

Now all we need is an under lever version to compete directly with the AirArms TX and Prosport rifles, the HW97 is already behind the AA offerings and only betters them when extensively tuned, if Walther were to bring an under lever version of this rifle that sure would be the gun to use for HFT and FT in the recoiling class.

 

 

 

 

 

 

Diana T06 trigger first stage travel modification

Can’t take the kudos for this modification but decided I will reproduce it here so you guys have a reference point to come back to for the “how too”

The Diana T06 trigger is close on HW Rekord quality but from the factory has a niggle that just was anoying me, the first stage travel was wayyyyy toooo lonnngggg, I think I had it measured over 12mm so something had to be done.

The cure is to replace the 2 adjusting screws with long 3mm grub screws so you can get more adjustment, I initially fitted 10mm long grub screws but have decided to swap these to 16mm long screws to ease the adjustment with the trigger guard in place. Either is fine though and you can get the first stage down to 1mm if you wish, i set 3mm with around 0.5mm travel for letoff on the second stage…it feels like I am pulling the Rekord unit now πŸ˜‰

Β  what you do is remove screw 1 and 2 and replace them with the new long grub screws, then its a question of adjusting screw 1 (1st stage) then bringing the second stage up with screw 2…be patient here, I had to go back and forth adjusting 1 then 2 then back to 1 again etc to shorten the 1st stage travel then bring in the 2nd stage with screw 2. So to be 100% clear here, adjust 1 then 2 then back to 1 and back to 2 untill you dial in a short first stage and the second stage breaks clean and crisp with no creap.

 

 

 

Here in black are the original screws and the silver is the new stainless screws you need..

 

 

 

 

 

 

 

 

 

As you can see they are around the same length but the grub screws have no shoulder so you can adjust them in further. I recomend some weak thread lock on these so they stay adjustble but do not work lose within the trigger.

I lighly polished the ends of the grub screws on some 1000’s wet and dry before use, just so they were smooth and even, this will stop them fouling as the trigger rubs against them.

last, if you want a lighter first stage you will have to either fit a weaker spring in position 3 or cut a coil or two off the spring supplied, i found with it adjusted all the way out it was still a little heavy for me…each to their own though…just remember to not go to light and make the trigger dangerous πŸ˜‰

 

 

 

HW85 part 5, final machining and bluing

The 85 has gone back to its owner now, he seems pleased πŸ˜‰ I forgot to add the last update so here goes.

here we have the piston rear bearing now machined down. the lip was also removed at the rear where the recess is for the screws for the scope rail, this was so there was nothing in the way thru could foul on πŸ˜‰

All that was left was to size the piston seal and set the power on the rifle, I set all rifles I work on to 11FPE with the most effcient pellet i find, they shoot nicer here, they kill just as effciently here (if you hunt) and they are safely below the 12FPE limit for the UK.

One last point i must stress, fitting a monster mainspring will kill your gun, here is what can happen to the cocking levers.

 

 

 

Β  Note the bend in it, this rifle came to me massively over sprung, the damage is clear to see, with a cocking lever this bent the rifle would drop the lever when cocked (it would come right out of the cocking shoe) and the breech on the barrel was touching the underside of the stock as the stroke length had increased due to the bend.

ONLY fit springs that just deliver the power you need, massively over springing guns does nothing but damage them….luckily this one was easy to straighten again.

Now straight:

Please keep an eye on this if you pick up an old rifle to refurb, a bent cocking lever renders the rifle dangerous to use πŸ˜‰

So, all that was left was to pack the bits up for bluing and drop them off with Colin Malloy. Colin does some amazing bluing, he is able to bring old rifles back from the bring of death and have them looking like new, infact in many cases better than new. Here are a couple of pics of the action, I did not have time to get well lit daylight shots for this one but will for the HW80 he is bluing now…these should show what good work he does though. You should notice I have used the larger HW80 barrel breech shims, you should just see one poking out between the breech and barrel, the reason for this is the previous owner had not looked after the rifle and used the gun with totally worn away shims, the side of the barrel was heavily scared by this and no amount of polishing would have removed all the damage…so I decided a larger shim would help spread the load better and is actually not see when in the stock at all.

 

 

 

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