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Diana 56 T/H Questions

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cjtamu

Member
Jul 8, 2022
1,430
2,160
Bay City, Texas USA
Just came in today. Gun in good shape cosmetically. Philippine made Bushnell and some unlabeled adjustable droop mount. Chrono printout I got has it making just over 9 FPE with JSB Exact 10.34. Shot some H&N FTT through it. Trigger is excellent. Shot surprisingly well considering the reticle is canted 10 degrees left. No recoil but there’s a little buzz. Don’t know if it’s been tuned down or if there’s an issue. Will put on chrono tomorrow and see what I get with FTT and start there. I actually have a ZRT spring for this platform but I think that’s too much for .177. A few questions: 1) When I tilt the gun down the sled moves forward. After I fire, if I tilt the barrel up to cock, the cocking arm travels about 3/4 way. Have to stop then finish cocking to get it all the way. Doesn’t happen if gun is level or barrel down when cocking. Is this normal?; 2) The plastic shroud between compression chamber and barrel will move fore and aft slightly. See pic. Any way to fix that?; 3) Anyone know what the finish is on these guns? I’ve seen it called Parkerizing. But, I remember reading something Hector wrote about the CCA 54 .20 not being Parkerized but something else. Wondering if that’s just those guns or the 56TH finish also; 4) Where is the manufacture date on these guns? Don’t see it in the usual Diana spot unless it’s covered by the stock. Looking forward to tearing into it and seeing what it will do. Thanks.

Edit: Found the post from Hector RE: the finish. It’s apparently a semi-ceramic finish that’s harder than Parkerizing and is what he used on the CCA D54 .20 guns.

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Yeah it sounds like its a bit of a mess from a tuning stand point. I'm suprised AoA would let it leave the store like that especially at the price they had it listed for...

What sort of velocity are you getting with the the 8.44 or 8.64 pellets?

The breech seals can be a bit weak on those guns so I would take a peak at that using a flashlight with the gun semi cocked obviously being very careful. If you can get a small block of wood in there to keep it open it probably wouldn't be a bad idea. Also, I've had pellets get stuck between the compression tube and barrel area that keeps the gun from completely closing and sealing. Worth a check. Aside from that, it definitely sounds like some investigative teardown is in order. Its a pretty simple gun to work on which is good news.
 
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WOW. 9 FPE? WOW
maybe someone wanted to shoot 10M?

Definitely check the breech seal first. (as suggested above)
Might be a broken spring?
From the behavior of the action. Sounds like the ball bearing retention adjustment needs to be tweaked. Steve Herr just recently posted a nice write up on his 0.20 RWS 54 project and how to modify and adjust the action.

Steve Herr's full tune of a 0.20" cal DIANA 54

More than 1 year in the making. Hope you enjoy! https://www.ctcustomairguns.com/hectors-airgun-blog/the-020-cal-diana-54-project Keep well and shoot straight! HM
www.airgunnation.com www.airgunnation.com


keep us posted.
 
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Yep. Broken spring and breech seal were the first 2 things I thought of, especially with the weird cocking behavior. I’m not sure how the sled affects cocking so not sure if it being mis-adjusted could cause same. No idea on velocity with other pellets yet. All of my Diana .177 guns hate JSB pellets. So loose they’ll fall out when cocking. Spray them everywhere, and about 1 FPE less than comparable weight H&N. And the 10+ gr pellets run about 1 FPE than 8 grain. So, maybe I get 2 FPE back and it turns out this gun was tuned sub-12, but I wouldn’t bet the farm on it. Sqwirlfugger, no idea. You’d think when they got the 9 FPE they’d have at least tried some other pellets. They don’t take them apart, just test fire and chrono. The other “90%” gun I bought from them is back at their place being re-sealed because it got here empty and wouldn’t take air. To their credit, they issued RMA and are fixing. Would just be nice if I could pull these 90% guns out of the box and have them shoot properly LOL.
 
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I would find out whats wrong and give them a ring if there is something broken. Like you said, it may just be tuned sub 12 for Field Target. I'm sure they have warranty parts on the shelf for it if needed. I get that it was bought as a used gun and all but you bought it from a reputable source not Bubba from the classifieds. I'd expect it in at least full working order OOB (unless otherwise stated of course. I saw the listing but don't remember how it was worded)

As far as the sled is concerned, play with the tension some but don't worry about it seeming too loose. If it groups well, it groups well. The last match I shot at Hector was shooting his 54. Before every shot he would push the action forward manually so I assume as that power level, on the looser side may be best. I could be wrong though. I'm sure he has quite a few things done to that gun that are beyond my knowledge base.
 
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cjtamu said:
Spring and piston seal look good. Can’t say the same for the breech seal. Was getting 10 FPE with FTT and guessing this is why. Anyone have a favorite method for removing? I’ve seen machine screw and drill bit mentioned.

View attachment 343819
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I use a coarse thread wood screw. Thread it in til it grabs and yank it out. I also have a little steel plate with a hole drilled in it that I slip over the screw and use as a slap hammer to help tap the seal out if its too tight.
 
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cjtamu said:
1/4” drill bit got it extracted. Now I just need to know how deep to set the new breech seal because the old one kept sliding out backwards so I have no idea. Ready to reassemble after that.
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Tap it in until it bottoms out, then make sure you have the proper amount of pressure when you close the cocking handle.

Steve
 
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cjtamu said:
@Nitrocrushr do you have a write up somewhere on how to pre-tension the tube/barrel sleeve when using HPM? Hector thought you did but I can’t find it. He gave me the basics but if you have a write up I’ll gladly read it.
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I have done write-ups on setting up the Harmonic Tuner, but I don’t recall anything about adding pretension to the sleeve.

Steve
 
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Nitrocrushr said:
I have done write-ups on setting up the Harmonic Tuner, but I don’t recall anything about adding pretension to the sleeve.

Steve
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Think I misunderstood his email. Believe he was talking about how to add o-rings and test as discussed in your article. He told me when changing number of o-rings to be sure to install HPM then stand the gun on its muzzle to pre-tension the barrel before tightening grub screws. Easy enough. I also bought a CF sleeve to test.

@pogeybait does yours only have one rivet in the receiver? Both of Steve’s have 2, but mine has only one. Believe the ones with a single rivet are a little older.
 
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cjtamu said:
Think I misunderstood his email. Believe he was talking about how to add o-rings and test as discussed in your article. He told me when changing number of o-rings to be sure to install HPM then stand the gun on its muzzle to pre-tension the barrel before tightening grub screws. Easy enough. I also bought a CF sleeve to test.

@pogeybait does yours only have one rivet in the receiver? Both of Steve’s have 2, but mine has only one. Believe the ones with a single rivet are a little older.
Click to expand...
Not sure. Will have to check.
 
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