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

Busy with projects but will be bringing new posts and info soon

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.










  • Don’t forget to blog the barrel choking 😉

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