Diana 56TH .177 - AirGunTec 22mm Skirtless Conversion

Part 1



Well, after numerous TX200 and Pro-Sport projects, I have moved to something a little different. After seeing stellar results from another AirGunTec converted 56TH I knew it was a project I wanted to tackle. I happened to find a great deal on a brand new 56TH .177 ($550), so I quickly picked it up. A few days later my beautiful 56TH arrived. It is a brand new 2015 vintage rifle, RWS badged. Knowing that Diana had changed hands recently, I reached out to Hector Medina to verify some facts about this rifle. This appears to be what he called a "transitional rifle", made in the old Diana facility in Rastatt Germany, but with a new barrel from the Ense facility. A beautiful rifle...and heavy. The weight of this rifle with my scope and mounts is 13.25 pounds.



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I took some shots with the rifle so that I could have a comparison of the before and after the 22mm tune.



Observations;



The rifle had substantial spring twang

The T06 wasn't too bad out of the box, but did have a very long pull with a fair amount of creep

Cocking Effort was heavy

The rifle had some jump to it, although most was absorbed by the slide mechanism. But saying that it was "recoilless" would have been an inaccurate statement



As you will see later in this write-up, I ran some recoil sled testing so that I could document the total movement of both action (on the slides) and the stock.



The Diana rifling is quite different than the typical LW rifling I am used to in my Air Arms Springers. Here are a couple photos comparing the Diana rifling to the LW rifling in one of my TX200's;



TX200 Lother Walther Rifling



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Diana Rifling - Notice the much wider rifling lands and narrow grooves



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Not having experience with this rifle, I had to do some research before digging in. When I was comfortable enough with the task before me, I began the disassembly.



After careful disassembly, I packaged up my Compression tube, piston and spring guide and sent them off to Tony Leach at AirGunTech for his 22mm skirtless conversion



While waiting for the kit to be returned, I went to work on some other things (trigger, slide mechanisms, etc).



First up was the T06 Trigger



T06 disassembled



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While honing the trigger sears I noticed that the bottom sear had a rough indentation right on the surface where the stage 1 and 2 trigger screws sit. Not good if you want to dial in for a nice light, smooth pull. I removed the indentation and honed to a mirror finish.



Bottom sear - before



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Bottom Sear - After



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I ordered a spare bottom sear from TW Chambers, and it had the exact same indent, so apparently this was present on a number of bottom sears over a period of time.



At the recommendation of Tony Leach, I replaced the trigger cap screws with grub screws. I found that the screws from a factory TX200 trigger were a drop-in fit, polished ends and all



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I borrowed Hector Medina's idea and added a tiny grub screw to the trigger tab. This enabled me to have an adjustment for reducing the length of pull on the first stage



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All back together, and after some fine tuning I had a VERY crisp trigger with a much shorter first stage, absolutely no creep and a nice crisp break at only 8.2oz



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Here is a short video clip showing the trigger pull







https://www.youtube.com/watch?v=7mfO6WlcX3I







With the grub screw adjustment in the trigger tab, I was able to reduce the reach to the trigger by over 5mm



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I later borrowed Hector's idea of installing Star Lock Washers on the trigger pins to keep them from moving out of position and rubbing against the metal liner inside the stock. Mine did slide out of position and rubbed the metal. The installation of the Star Lock Washers solved the problem. The trigger pins are 2.5, 3 and 4mm.



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Next up - The slide mechanisms. One thing I noticed out of the box is that the slide mechanism was very firm, and rough. This required quite a bit of pressure to release



Upon inspection I noticed the machining marks that the ball bearings were sliding on - See the machining marks in pics below;



Rear Slide



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Front Slide



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I disassembled the slides, gently polishing up all surfaces including inside of the slide blocks. I also used wet/dry paper and polished the machining marks out of the slide bracket surface. They are now very smooth.



I lightened the spring tension substantially. Note: When doing this I had to modify the grub screw for the spring tension in the rear slide. If you back the slide spring tension off too much, your rear stock screw will bottom out on the set screw rather than compressing the rubber washer. I modified both the grub screw and the rear stock screw to enable me to run lower slide friction without having my rear stock screw bottom out when tightening.



I know there is some debate on this one, but I lightly lubed the sliding mechanisms with Weapon Shield. Extremely smooth sliding action now



In addition to this, I used the idea I saw in the link below and installed o-rings to reduce the rear slide lock-up depth. This allows the slide to lock lightly, rather than having the ball drop completely down into the detent. Much smoother release of slide and very well suited for bench shooting. Instead of adding a single o-ring to the front slide as shown in the link below, I added 2 o-rings to the rear slide.



http://www.eddiecolwell.tzo.com/RWS-54.htm





Here are the slides, polished and complete



Rear slide - After



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Front Slide - After



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After the slide work was complete, I felt some resistance towards the back of the slide travel. Upon closer inspection I noticed that the plastic trigger housing was rubbing within the groove in the stock. Some inletting on the leading edge of the groove in the stock remedied this problem. I also removed some material from the very bottom of the plastic trigger housing.





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In addition to this, the cocking handle was rubbing against the action reset arm that sits on the right hand side. This is detailed in the link I posted above. You can hear the metal sound when closing the cocking handle, and you can also hear it rubbing when sliding the action back and forth. This adds resistance to the slide motion. A small piece of rubber pressed into the inside of the cocking handle took care of the problem. The handle now rests quietly against the thin rubber insert, and no more rubbing.





Here is the metal arm that the handle was rubbing against



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Small piece of rubber about an inch long took care of the problem



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The small piece of rubber was wedged into the end of the cocking handle. The rubber stopper sits right against the metal pull rod that is connected to the Compression Tube



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