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

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

  • Hi absolutely brilliant article, have already started machining this mod up, have a 48\52 and totally agree at sub 12 fpe it still kicks worse than a centre fire.Cheated a little, use the old T01 piston front as I have recently fitted a T06 trigger.Just need to machine up a delrin rear guid and plug to attached the piston heade extension. Will let you know how it pans out.

  • The piston with the extension does work OK but the piston weight is a little high, its actually worth considering machining the piston to have a new rod that’s longer and machining the rear flair off the piston more so that you remove more weight, of course you add the sleeve with a rear bearing in acetal anyway.

    I found the piston weight to be key with a short stroke, around 260 to 265g is where you want to land with a top hat installed.

  • Hi there! I really hope you see this and reply. A dealer here has stock of a .177 48 in 16J/12 fpe format. This is the latest T06 Trigger version.

    Do you know if DIana uses only the restrictor to limit power? Or have they started modifying the internals as well.

    I have a full power .22 Diana 52 and love the way it shoots. Wanted to buy a .177 but I’m worried if it will be as smooth as it ought to be.

    Looking forward to your reply.

    Mo (mohamed.tassem@gmail.com)

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