This would lose some spring room but in theory would counter piston bounce.

O ring placement would need to be experimented with to ensure enough compression happens, this is just a rough idea to get some creative juices flowing.

Most of the early projects at AGT have been with HW rifles, HW95′s and 97/77′s and HW80, of  late however I have entered into a love affair with Diana rifles, notably the M52/54 and the 440TH/430. I am sorry to say I won’t be testing or tuning the T05 or earlier triggers, I personally have no interest in them and update all my guns to the T06, its an excellent trigger and once set up correctly is the match of the Rekord from HW.

Recent rifles I have added to the collection are 2x 440TH”s which have been tuned in different ways, one has been sleeved to 25mm and fitted with a modified Walther LGV piston with 80mm stroke, the other has a Diana 52 piston (which shortens the stroke to 78mm) which is lightened with bearings added to 250g…and I have to say right now the 28mm D52 piston gun is the sweeter. I did try 68mm stroke on a 28mm bore but the cocking effort was was to high with the preload needed on the spring..the shot cycle however at 11.3fpe was stunning…nothing i have tuned here came close.

So, I compromised at 78mm stroke and it is still an exceptional rifle to shoot, extremely accurate. However I have lengthened the under lever by 75mm or so and reworked the barrel catch/muzzle break to give me a little more mechanical effort when cocking the rifle. I have decided to do the second 440 the same way to will detail the build here in case any of you guys wish to copy what I have done. Its a radical alteration to the 440 but is in my opinion needed as the cocking effort even on sub12fpe rifles in .177 is substantial….tennis elbow anyone?!!!

The other main Diana I have worked on is the M52 and the M54 Airking, I will detail the Airking tune after the 52 tune as they are very very similar (essentially the same gun). I managed to pick up a second M52 Ultra K with the intention of tuning it, selling it and using that cash to pick up an .177 M48 pro Blackline from Germany, this  as far as I am aware looks like it may have the ultra k 300mm barrel and is the same basic chassis as the 52 so i would just swap the stock for a custom one…however a mate gave me a .177 52 firebird as a “thank you” so I have reworked this instead. I will detail the build spec although I will be altering the gun inline with my testing, right now the gun has a 270g LGV piston with 69mm stroke, it makes power supremely easily BUT I have made the decision to push the stroke to 75mm, this will allow me to ease back on the preload a little on the spring…right now it just feels a little too fast. Also the old Firebird stock…I just can not get along with it, its too sporter for me so im looking to have a go at carving something similar to the M54 laminate stock with some alterations to make it suit me better.

One interesting thing I have found tuning Diana rifles for UK sub12 spec is the pistons I use, it does not seem to matter whether i stay 28mm bore or sleeve down to 25mm bore, the stroke looks to be the same with both (or close) as does optimal piston weight. With the 440TH under lever rifle the 28mm 52 piston gun is actually sweeter to shoot than the 25mm piston gun even though its power output is marginally higher. I did find the Diana OEM piston seal to be very good, however  its not as consistent as the Vortek red Diana seal which i found to be as consistent as an O ring…really quite stunning, being a large seal it gives the soft cushion however which many like. I may in the future explore a home brew 28mm piston for the bigger side lever 52, however right now its so efficient at making power the easy route is to renew the rod on the LGV piston and sleeve down to 25mm.

When I finish the second 440TH a decision will be made which I prefer and the other will be sold, it only makes sense to keep both while I experiment. Out the 2 52Ultra K .22′s I have again one will be sold once I finish fine tuning them…If Diana do produce a 52 Ultra k in .177 i may jump on one, the Firebird while nice has had a hard life and will never look like new.

So stay tuned, I think I will start with the Diana 52 revisit with .177 update over the next week or so.

Its been a while…remember this post?

http://www.airguntech.com/?p=465

Well Its been on the back burner for a while and I decided I have had the rifle long enough here and should be getting it finished. Specs for the build were exactly as I outlined in the post above except for the transfer port, this was opened to 3.6mm over 3.3mm.

Spring was to spec above, I had to make a fresh guide and tophat for it as its smaller ID than the OEM spring…the result with approx 50mm of preload is 11fpe..so bang on the money. Tested pellets werte Daystate Li’s (Crosman Premiers), Superdomes, Geco and Hobby and RWS Superfield. 10 pellets of each weas pushed thru the gun and then 10 shots over the chrono…10.8 to 11.1 with all of them, highest seen velcity was 11.3fpe and this dropped once the rifle settled with the pellet under test. Recoil is light, very little surge…its actually quite nice to shoot and I will range test it to see how it settles…right now im quite pleased how it came out and for me a blueprint tune is now set.

Colin has a new number, please contact him only on this new number for now.

07565582549

He is still bluing but as far as I know is not rebuilding the rifles, so you send him a kit of parts and he blues those parts for you.

Been looking for an alternative seal now for a while, something off the shelf, easy to find and that works as well as an O ring if possible with minimal lost volume. Scouring the Hydraulic seal suppliers I came across Kastas.

Click the pic for a link to the site, I highlighted the seal I will be testing next on 25mm pistons.

The reason for this seal was its size, it is around the same size as an O ring but is made of polyurethane, the pressure groove is tiny so the lost volume should be minimal and the seal sits in an easy to machine flat bottomed groove. My plan is to test the seal with flat fronted pistons (bronze piston nose) running tight tolerances to minimise the lost volume even further.

Some addition pics of the seal.

Will update with some results and installation pics as the seal, as you can see its pretty small.

Back in July2012 I had the idea of building a Weihrauch HW35 fitted with a Walther LGV rotary piston and that’s just how it stayed until Christmas — just an idea.

Then in December I was fed up one Sunday  and decided to de-braze a HW35 cylinder from its breech block in order to show how the cylinder was made and to highlight the grooves round the breech block which give rise to the porous cylinder problem on the 35.

As can be seen the original Weihrauch breech  it pretty long with 20mm of the breech brazed inside the cylinder with a total transfer port length of 26mm. With the cylinder de-brazed and armed with a few LGV piston measurements from Tony I was able to work out if the conversion of the HW35 to rotary LGV piston was possible. Everything looked good to go so I ordered a 16joule Walther piston kit from Germany (via Tony) and a short length of 30mm OD X 25mm ID Hydraulic tube. Prior to machining the breech block plug down I was already aware that I was going to break through into the breech latch slot and the breech stop hole — I was quite happy that these problems could be overcome by welding.

So I machined the breech block down by about 20mm:-

As can be seen I took the precaution of bolting a spacer in between the breech jaws to stop them distorting when machining or welding.

Once the holes in the rear of the block had been welded shut I machined the breech down to leave a 0.5mm ridge on which to locate the 25mm ID tube.

I could then clamp the 25mm tube onto the breech block and weld it on and then machine down to end up with a breech block with a 6mm long transfer port attached to a 25mm ID X 30mm ID cylinder.

Now before welding this back into the original HW35 cylinder I decided to machine the piston to suite its new home.

With the original LGV piston seal the piston was too long and would cause a large gap between the cocking lever end and the rim on the rear of the LGV piston. So I decided the simplest option was to machine the seal retaining hub off the front of the piston and machine up a new bronze O ring piston head.

With the piston sorted I was then able to weld the new breech arrangement into the original HW35 cylinder.

I then machined the weld down and linished the joint.

So I ended up with a HW35 cylinder with a 25mm bore which opened out to 30mm at the cocking lever slot enabling an altered Walther LGV piston to be used

Machining the front of the breech block not only enabled the Walther piston to be used but it reduced the gun’s transfer port down to the length of a HW77 transfer port at 6mm.

Event though I had the D52 shooting quite nice, i knew it could be better…with the Walther LGV piston being such a universal base for conversions I decided to see if it could get it to fit in the D52 and by making up a new longer piston rod reduce the stroke…and of course sleeve the compression tube down to 25mm

First job was the sleeve the compression tube, did not get any pics of this as we all know what  a piece of steel tube looks like machined square on both ends and cleaned/polish. The tube used is 28mm OD 1.5mm wall high precision hydraulic steel tube, machined square and true both ends, the comp tube open end is relieved a little so the piston is easy to insert, the end that sits on the breech is as flat and true as I could get it…the tube is pressed home and secured with loctite thread lock. Cut this sleeve +2mm length, measure the internal length of the compression tube and just add 2mm, it will clear the skirt on the piston by around 4mm

Now..the D52 has a central transfer port, this means the Walther Piston seal can NOT be used for this conversion, I opted for the Vortek Vac25 seal (although a second hand one showing some signs of wear..will get changed when the next order comes in). If you are considering this conversion then you really do need to consider the added cost of a replacement seal as well as buying the LGV piston.

Next job is removing the rear bearing on the piston and machining a new one. The ID is the diameter of the groove cut into the piston, for me this was 27.20mm, the OD is 31mm, the width is around 4mm but measure the groove as you machine a new bearing to suit. So you are replacing a 30mm OD bearing with a 31mm OD bearing

Once done you have to remove the OEM rod from the piston, I held the rod in the lathe and heated the nose of the piston till it started smoking then using some grips wind the piston off the rod..they are loctited on. The thread is M8x1mm so if you want to clean out the threads in the piston nose you are going to need an M8x1mm tap. Next reproduce what is on the end of the OEM piston rod onto a nice fresh piece of 10mm OD silver steel bar that is precut to 210mm long for .22  (205mm for .177)

The rods total length is 210mm, the sear engagement point lands at 207mm for .22 and will be at 202mm for .177.

This is the piston nose end, top OEM bottom the one I machined..it was identical but i had to lengthen stroke by 3mm hence the thread on the bottom self machined piece is shorter.

As you see what you end up with is quite a bit longer, remember this rod here is for a 70mm stroke for a .22 D52 to UK spec.

Here is the trigger sear end, copy exactly what is on the Diana piston remember…NOT the walther piston .

Remember you have to harden this after polishing.

All built up with fresh loctite on the threads you should end up with something like this.

Now, the spring to use is the full length spring you get with the D52 Ultra K here in the UK which pretty much is the full FAC spring, I used the OEM rear guide but shortened it by 10mm (off its nose) so I could install a top hat. This top hat has 3mm step on the end and I added an additional 3mm of preload, total preload on the spring is approx 45mm. Diana deliver the guns dry internally, make sure to grease the spring up and the guides, the piston seal just needs a tiny smear of moly lube or SM50 with the same on the front nose bearing on the piston..on the rear bearing i used high moly content grease.

So thats about it, rebuilt the rifle and just started tests, its touching 11fpe with 14.5gr RWS Superdomes. I expect it will gain 0.1 to 0.3fpe as it shoots in. The shot cycle is nothing short of amazing, 70mm stroke on this 258gramm piston in such a large gun means it bearly recoils…silky smooth to shoot.

I will update once I shoot the rifle at the local club over the coming week. I have to say it feels NOTHING like a stock Diana 52 to shoot, it feels much like a heavily tune HW77 mk1, for me for UK use this has to be the ultimate tune for the D52.

Finally settled the .22 down, here is how the rifle ended up.

Refitted 16inch HW90 barrel (same as 16inch HW80 barrel although the bare 90 barrel is slightly lighter weight)

Added 280Gram barrel shroud (finishes flush with the end of the barrel) its just to add weight

Originally the short stroke using the LGV piston seal was 11mm, I have now swapped the LGV seal out for a 25mm Vortek seal which added just over 2mm stroke..so rounding down I have increased stroke by 2mm  so now only -9mm overall.

Changed the spring for new unit with 3.25mm wire, 20.5mm OD, approx 240mm free length (I will count coils and update) This spring has fewer coils per inch so is stiffer, its also slightly longer than the spring I was using originally and needed no extra preload. Power remained the same with RWS Superdomes however power increased with AA fields by 0.2fpe.

End result is a slightly faster firing cycle, hold sensitivity has massively reduced although the .177 is almost not hold sensitive at all…the .22 is now MUCH easier to shoot. I will swap the straight setback trigger bade for an extra set back unit from Rowan Engineering which I feel will help a great deal also.

For now its sat back in an OEM stock, I find it easier to shoot in this stock over the CS800 it usually sits in, if this proves still the same the CS800 will be up for sale. If the rifle does stay in an OEM beech stock I will modify it somewhat like I have with the 0.177 in the mk1 stock…or i will look our for a mk1 HW80 stock and modify this.

Final thoughts on tuning the HW80, the 305mm Carbine barrel thats popular now is to short, I tried 2 on this .22 with one being fully shrouded, while good barrels they just did not help balance the rifle well and are not as efficient as a 16inch barrel. I could tell right away with the 16inch barrel reinstalled the gun had settled down considerably.

The .22 HW80 LGV piston conversion needs more work that the .177 for UK sub 12fpe use, for my USA readers or those with FAC you could leave the stroke at 79mm for the .22 but run the rifle up around 16 to 18FPE (It will do this power ) I would imagine the rifle would not feel any different to the firing cycle i have with the .177…seriously smooth to shoot. For UK use the .22 looks to need 70 to 71mm stroke (approx 34.5CC of air)

The single thing I may try is converting the piston to an O ring seal, this will quicken the shot cycle even more and may dial out what hold sensitivity there still is…its slight though so may not be worth the effort….its under debate

When I converted the .177 80 to LGV piston I also completed a .22 conversion at the same time, till now its been somewhat hold sensitive, to the point I thought the barrel was faulty…tried 3 barrels and all had the same issue…so looked deeper.

The .177 conversion is much quicker than the .22, if you keep the 79mm stoke the conversion gives with the .22 conversion you may have to lose 2 full coils off the LGV spring, its nice to shoot but you may find like I did the hold you are used to is just not good for accuracy. A little frustrated by the gun I decided to shorten the stroke in the hope that less air more spring would get the gun to behave a little better…so I decided to just jump right in and go down 10mm stroke, which is a lot!

I in fact went down 11mm to 68mm stroke, in the thinking I could shorten the rod 1mm at a time if more stroke was needed…as it stands there is no need, the AGT80 conversion is so efficient it will make 11.5FPE in .22 from 33CC…I kid you not Best pellets for power look to be 14.5gr Superdomes, Hobby lands at 11 to 11.2, AA fields 10.8, 19.2gr Baracuda Hunter Extremes give 11.3 , I will be trying more pellets over the week. Not shot Superdomes from this barrel before so praying they are accurate.

With this 11mm drop in stroke you still need to lose 1 full coil off the LGV spring. I went 2 full coils and added 8mm of preload so going 1 full coil off should be just about right. You could always go 1 coil off and 1 crushed coil and tune up with preload washers, however remember the piston is already heavy, use synthetic washers to pack up preload and consider adding them on to the rear guide not in the piston BUT remember they have to have an OD that will fit into the piston

The drop in stroke is not needed for the .177 conversion, although those wanting to quicken up the conversion even more way consider losing 3mm to 5mm off the stroke on the .177 conversion.

Will update once the gun has settled down.

Just 2 quick pics to show how she looks now, bluing by Collin Malloy RFD here in the UK and because I like the Mk1 80 stocks I decided to just rework the woodwork she was in and have something a little different.

The dark wood I inlet into the stock is India Rosewood, I had it to hand and thought the contrast would be nice..its different although I know some will not like it.

So, final specs for the gun.

1980 HW80, started life as a .22, action was painted, stock was dinged and scratched, cost me £120

New 410mm Long .177 barrel, dovetails filed off

Self made shroud, not showing the internals although they are not special, extends the barrel 50mm…very quiet

Rowan Engineering fully setback trigger blade.

Walther LGV (the new one) piston, reworked main sear on trigger, 25mm sleeve, 3.6mm transfer port, reworked LGV mainspring, power set to 11.2fpe for UK use.

Just put her back together after getting her back from Collin, have to say I really like this one.

Total outlay for the project.

Gun 120

Barrel 90

Trigger 36

Bluing 60 (no barrel was blued hence cheaper)

Rosewood 10

Oil 50p

Steel for shroud 4

cocking shoe 8

Piston  and spring 45

Guides material 4

total £369.50

Normally i would not have to buy a barrel so normally this type of project would have cost £250 to £280 all in to better than new condition.

Obviously my time machining was free