RWS Diana 52 - tuning update...

[Hellequin]

A bit of an update on my tinkering with the 52 'Ultra Carbine'...

A few weeks back I posted this thread: http://www.airgunbbs.com/showthread....tuning-options asking for advice regarding 'fettling' my 52K.

When I got the rifle it was standard and, as far as I'm aware, had never been apart. It was in great condition but when I chrono tested it I was surprised & a bit disappointed to find it was only doing a shade over 9ft.lb power wise with Superdome pellets. It was also a bit twangy, hence my original post on the linked thread.

As already discussed on the original thread, there are quite a few options for this rifle with varying costs & levels of work/expertise required. I decided to go for a 'home tune' option and bought a Tinbum kit and some new seals. In the kit is a tophat, spring guide, washers, lube & a 'Diana Export' spring. I also got from Nick one of his prototype short stroke extensions for the 52, but more of that later...

Whilst the rifle was apart I discovered that the breech seal was damaged so I removed it to fit a new one. I also removed the 2mm transfer port restrictor. This allows the rifle to breathe through the original size 4mm TP.

Unfortunately, once the Tinbum kit was fitted (without the short stroke extension) the resulting chrono test was a bit scary, as the ft.lb number started with a '2'... Given I no longer hold a FAC, it came back apart there and then.

I decided to rebuild using the short stroke extension, which is about 20mm and to take two coils off the spring which came with the Tinbum kit to see how I went on. Bear in mind that the spring in the kit was about 30mm LONGER than the spring which had come out of my rifle and had 33 coils total...

It was still way too hot, although it had reduced power by 3ft.lb. It came apart again and another 3 coils removed. Rebuild, test and.... still hot! I was getting somewhere though as it was down another 4ft.lb. The rifle was stripped again and another two coils came off, by which time I was getting worried that the spring was going to be too short. I was also getting fed up of re-finishing & polishing the end!

I put the rifle back together with the spring now measuring about 235mm and down to 26 coils. Very little preload compared to the original as you can imagine, so it was much easier to assemble. The chrono test at last put a smile on my face; an average over 10 shots of 590fps with 14.5gr Superdomes meant 11.2-11.3 ft.lb!

A lot of work but worth it to keep the rifle 'legal'. I'm now going to put another couple of hundred shots through it and then test again. If the power rises slightly there's room to leave it alone and if it drops I can add a preload washer or two. Firing cycle isn't bad (I'm sure it'd be better with a 22mm conversion, but that's over £200's worth of work) and certainly miles better than the twangy thing it was when I bought it. The rifle is in good nick cosmetically and accurate, so it deserves a bit of effort, I reckon.

A few points to bear in mind:

1. These rifles are BEASTS. If you're going to tinker, it goes without saying to make sure you use a chrono and if you remove the TP restrictor you WILL need to make other adjustments, either a different spring, short stroke or both. BE CAREFUL & stay legal.
2. I got some good info from a blog by Tony Leach (Airguntech) detailing his work short stroking a 52. He's done much more since then with 25 & 22mm conversions but his short stroke info was what I was interested in. Bear in mind though that my 'prototype' SS extension from Tinbum was only 20mm whereas Tony used a 38mm extension along with a standard Diana 280 spring which he still shortened by 2 full coils.
3. Firing cycle. It's still not as 'smooth' as I'd like (but it is much better) so I'll see how it beds in. It may be that the spring is now too short and it might be better with a short stroke of 38mm and one of those shortened Diana 280 springs which Tony used, although to be honest if I had more work done to it now it'd be the full 22mm conversion.

Anyway that's it done for now and I can at least enjoy shooting it, until some other toy catches my eye...