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

Diana 280k 0.177, Rough from new but tamed in an afternoon.

Picked up a new Diana 280k from the shooting show here in the UK in February, initial impressions were its a nice gun to look at but bordering on horrid to shoot; lets look at the gun before I explain what I found wrong.

Diana only list the 280 and 280 classic on their website,   http://www.diana-airguns.de/index.php?id=274&L=1&width=1920&height=1200    the 280k looks to have been a UK special order along with the 280 Professional which eventually made sale in other countries also. Basically the 280k is a shortened 280 with screw cut barrel and no open sights.

RUAG, the UK disty for Diana do actually show the 280K here

So what is there to look before we list the dislikes, well, it has the T06 trigger with metal trigger blade, this is a nice trigger although I have not as yet managed to dial out the lengthy first stage, second stage though is awesome, no creep and nice light let off, so overall if I do not manage to shorten the first stage im not going to be overly worried…I will just get used to it.

The stock is lovely, its plain Jane beech but the shape and how it handles are bordering on awesome, the balance is just infront of the trigger guard on the rifle I have here so a comfy shooting position is assured…but now the bad points.

 

1 it was severely boingy

2 it was really hard to cock…remember this is a sub12FPE rifle but it cocked like a 24FPE Theboen Eliminator…really quite hard on the arm.

3 returning the barrel to the locked position was really hard work. it felt like it was grinding its way back from around half way to just before it snapped in position.

4 Power was low, sub 10FPE over the skan chrono here with all pellets including SuperDomes which look to be its favourite food.

After pumping 200+ pellets thru it my arm felt like it was going to drop off, severe pain in the left elbow..this really was not a nice gun to shoot…so I stripped it.

here is the gun how I shot it the first day…muzzle brake is off my HW80, I added it to use as a cocking aid…it helped but no where near enough. Scope is the awesome Vortex 3-7×35…really nice glass and the ideal weight for this little carbine.

  As you can see, its a sleek sporter, nice laser cut skip chequering and a medium height cheekpiece, it suits low to medium mounted scopes well.

 

 

 

 

Lets have a look what’s on the inside.

 

 

 

 

Now, upon stripping the gun I noted that the spring was totally bone dry, no lube what so ever. The piston seal was massively over tight in the compression cylinder also…it would have taken thousands of pellets to bed the gun in. The rear spring guide is well made and I decided to reuse it although it would need altering to suite the new spring I planned on using. The last pic here shows the T06 trigger, it comes out VERY easy in 1 piece BUT you do need a spring compressor, I used my lathe for this using the tail stock to wind out the trigger block.

Next I started to look more in depth at the piston, as mentioned it has an oversized piston seal but I also noted it was out of round and galling on the compression cylinder. The following 2 pictures show this although the second pic shows it the clearest.

You should clearly see in the first pic there is a gap between the piston body and the rifle action BUT this vanished when the piston is in the compression area of the action.

 

 

 

 

 

I decided to remove just under 1mm from the piston body right behind the piston seal.

The piston was 27.81mm dia and out of round, after machining I had a round piston of 27mm dia, should be well enough to clear the compression tube.

 

 

 

 

 

Next was the piston skirt, a few thous has to come off this to allow for the rear bearing I am adding, the only issue is Diana have really hardened the piston skirt to the point its close on un machinable without annealing, I did not want to do this so I persevered using plenty of cutting fluid followed by a polish, I just gained the clearance needed and reduced the length of the piston by 3mm.

before

 

 

 

 

After

 

 

 

 

 

Next its time for the inner piston spring guide and rear bearing. The Diana OEM spring has an OD around 22mm, I decided to change to a Titan XS No7 spring with a 20.5mm OD and 3.2MM wire, this is quite a stiff spring and was chosen as the Diana does not have have a long stroke.

Same exact configuration I use on the HW springers, guide is machined from ACETAL tube and glued into place using industrial superglue with a plastic to metal primer.

 

 

 

 

 

Glued in ready for machining

 

 

 

 

 

Now machined to exactly suite the action

 

 

 

 

 

At this time I also machined a front spring tophat guide and slip/thrust bearing from Delrin

All that was left was to resize the piston seal for a nice slide/glide fit in the compression tube and to reshape the cocking arm end so that it stopped galling on the inner spring guide. I also polished the sides of the cocking slot in the action for good measure. Now, I mentioned the OEM spring was to long with the action massively over sprung, well the new spring ended up being a full 5 coils shorter than the OEM spring. Its still a little stiff to cock as it does have a short barrel (a 280k Professional muzzle brake is on order to help with this) but it is noticeably smoother than it ever was before.

The compression tube had Honda Moly assembly paste buffed into its surface, a smear was added to the side of the piston seal and a small amount to the rear bearing on the piston. The ends of the spring were lightly greased also but NO grease was added to the length of the spring…its not needed 😉

The end result is a lightening quick lock time, slight nudge of recoil and a butter smooth cocking and barrel latching cycle…totally different to how it was new, its like a totally different rifle. Power is a conservative 11.1FPE with RWS superdomes which look the most efficient lead pellet around 8.3gr.

 

Overall I am pretty pleased with the rifle now, so much so I fancy having a go at a .22 version but using a smaller spring and moving to an O ring piston seal, I feel I could keep the lock time ultra quick this way but have a much easier cocking cycle due to the more efficient .22 needing far less spring than the 0.177.

 

If you fancy a 280K, RUAG informed me they have instructed resellers to discount the 280k down to £235 GBP…many will probably sell a little cheaper also. Its a good gun, has an awesome trigger BUT be prepared for a little work to get it buttery smooth to shoot.

 

 

  • excellent article i love the diana,s but you have said what every hunter and home tuner has known for years no new gun from them or any other manafacturer is any where near the 12ftlb limit!iam buying a 280 carbine in .22 cal for my birthday it is being supplied with a parker hale alloy sound moderator for an extra £25 on top of the £260 price tag i cant wait!!!!

  • just an add on to my earlier response iam fitting a power lock mainspring to mine which i pre compress on a home made jig for 1 week to allow for spring reduction and less pre load i did this on my diana 34 carbine and it stayed on 11.9ftlb with superdomes(.22)the whole time i owned the gun 3+years and just 6fps variation i only shoot around farm buildings so the .22 is ideal

  • 11.9 is a little to close for comfort, it will fly well over 12 with light weight pellets. You would do better tuning for a nudge over 11FPE…it will dispatch airgun quarry just as good trust me 😉

  • have to agree with you it was too close to the limit but i sold it to a gunshop who chrono,d it with the superdomes when i part exed it going to go for 11ftlb on the 280k as iam sure when bedded in power will creep up a bit i just want it smooth,consistent and accurate,i dont think pigeons or rats notice the power so much as the accuracy!i dont have a lathe any tips on how to improve my air rifle will be much appreciated Tony

  • sorry to keep hassling you(iam on my day off)will i need a slave pin for re assembly when rear block goes back in same as the 34sm?the safety spring/bar needed to be down to put the pin back in

  • no…just use a spring compressor to push the block in and hold it solid while you tap the pin home.

    I have an update to make on the 280k tune, I have now adjusted the trigger to feel and break just like the rekord trigger (in HW’s) all you need is 2 new adjusting screws and some setup time.

    I will add this info soon so you can see what to do

  • many thanks Tony i have looked at the trigger mod il bet your gun shoots so smoothly just out of interest will the titan No:7 be ok in my 280k because its a .22?

  • If I do a .22 I was going to use the no5 or the smaller no11, the no5 would need shortening, the no11 maybe ok at the length it comes shipped at.

  • Remember i make an inner sleeve that controls the smaller diameter spring…also a new top hat and rear spring guide as well. Its a package that keeps the spring compressing linear with no cant or buckle at all…this is really important. I can take a spring out after thousands of shots and its as straight as the day I put it in the gun

  • Hi Tony thanks for the info iam not sure what to do as i dont have a lathe its either put a full v mach tuning kit in and polish the piston bearing areas and size the piston seal to the cylinder or buy a no 11 titan xs and pay someone to make proper acetal guides i want to use my rifle for rook shooting very shortly but it must be run in and zeroed how much would you charge me to do the work?Any help would be greatly appreciated thank you.Tony

  • Hi Tony i have just purchased a Hatsan Striker 1000 in .22 calibre nice gun cheap and cheerfull accurate though but the trigger and internals where a bit agricultural to say the least!do you know of any mods for this gun i have stripped and cleaned it and iam renewing the internal components piston seal breech seal and titan xs spring for the Hatsan any advice is always greatly appreciated i would say in passing the anti bear trap was a proper pig to dismantle.All the best tony ashton

  • never stripped one, to get it smooth you need to measure the compression chamber diameter, measure the piston stroke and work out the swept volume. For sub12 guns you need around 40CC,if the striker has more consider having the piston short stroked till it produces 40CC and start your tune from there.

  • many thanks Tony as this will be my vermin/farm rifle iam setting it to 11ftlb as it mostly used on feral pigeons and rats the swept volume is over 40cc so i have taken your advice i have had the barrel shortened to 12″and threaded 1/2″unf for a better selection of sound moderators when its up and running il let you know the power and try to send you some pics of that anti bear trap and the state of the internals but its a £130 gun so its to be expected it has made a good vermin rifle for not much money though thanks again.Tony Ashton

  • Hi Tony, it’s the pain in the arse tosspot here from the BBS, I think I may have managed to get a 280k .177 from one of the BBS members that has been SFS tuned, just got to get confirmation of sale from him, it will be interesting to see how different the internals will be like from your gun to Tony Walls tuning, I hope the sale goes through as I’m looking forward to trying a 280 out. ATB Pete

  • Well the lure of the 280 was too much so after selling my AA S200 combo I then had the money to persuade Tony to part with his 280k (yes the .177 one in this very thread), all I can say is it’s a beautiful rifle to shoot and makes a very nice change from any of the HW offerings, this will be my dedicated hunting rifle and although it’s not been used yet in anger due to bad weather and the such I will be practising in my home range with it as much as possible until I can get out and go hunting.

  • reference your comments on hard to cock my Diana 280K was harder to cock than any spring gun I have ever owned, it actually gave me a sore arm and I had to use two hands ( I am no weed and do a physical job). It was again bone dry with no lubrication , it bucked and twanged like mad. I have sent of to Sandwell field sports so be interesting to see how it shoots when it arrives back. Looking forward to getting it back , its a nice , well balanced gun but (like many other makes ) clearly needs a tune to get the best out of it

  • Tony

    A while back in London you gave me some advice on my 22 – 280. I got it working by cutting a Airsporter TS01 spring down. Couldn’t get a cut down tophat in there as it wouldn’t cock.
    However shooting in the snow wilds of Canada at -19C it does around 506 fps, one test went to 556 fps. Since I can’t do the inside piston guide what do you suggest I do spring wise to get a bit more power. Need it for ground hogs?

    Thanks for your help…………………………………………..

  • you should see more power with just an oem 280 16J spring, I would take a look at the breech seal and piston seal and make sure they are doing there job before trying to squeeze a stiffer spring in to get more power.

    Ultimately the 280 is a short stroke 34, it may be worth you making a further investment on a 34 also 😉

  • A 280 is never really going to make more than 16J Bill, maybe try a little more preload

You can follow any responses to this entry through the RSS 2.0 feed.

Assign a menu in the Left Menu options.
Assign a menu in the Right Menu options.