Diana 27 velocity and tuning questions.

[Bayman]

Well...let's just see what the old guy can find in his musty folder of chrono work, lol.

Numbers below all from a Chrony Alpha, and are averages of 15-shot strings: pellet name and weight (grains); average velocity (FPS); extreme deviation (FPS); standard deviation (% of average velocity).

1. Prewar quarter-stock model 27, .177, made 09 26, interior condition unknown.*
RWS Hobby 6.9, 624, 11, 0.55
JSB Match Pistol 7.6, 589, 11, 0.61

2. RWS 27, .177, made 02 81. Never been opened, just basic maintenance.
1988
Eley Wasp 7.2, 677, 15, 0.54
RWS Hobby 7.0, 667, 34, 1.43
RWS Superpoint 8.0, 630, 34, 1.30
RWS Meisterkugeln 8.4, 618, 16, 0.81

1991
RWS Hobby 7.0, 676, 32, 1.01
Crosman Pointed 7.9, 619, 25, 1.20

1995
Ruko Match 7.5, 654, 13, 0.65

2007
JSB Express 7.9, 615, 16, 0.84

3. Winchester 427 no. 1, .22, made 02 73. Probably never opened up.
RWS Hobby 11.9, 521, 23, 1.12

4. Winchester 427 no. 2, .22, made 10 73. Very smooth tune from previous owner.
RWS Hobby 11.9, 499, 28, 1.73

Just an editorial note, an SD under 1% is springer match gun territory. The consistency that model 27's get says a lot about the quality of Diana's springs and seals in the old days.

* The power and consistency of this ancient rifle are amazing. The thing shoots so smoothly, I would have guessed the power was in the 400's...!

Thank you Mike!
That's all great useful information. I was surprised at the power and consistency of this gun on my initial test. After 2 shots to check for function I chronographed the next 10 and I believe the ES was like 8. Not bad for an old dieseling gun with a leather seal. It's really a nice little gun. Well other than it cocks like a marble grinder and the cocking arm skips over every coil on closing. I think that's because of the bent steel spring guide. I'm gonna have to come up with a fix for that by figuring out a spring that's the right rate and length while leaving enough room for a new guide that will work with the trigger and still clear the cocking arm. Fun

Also I bookmarked that fantastic thread where you go over the triggers so thoroughly. I will refer to it when I get to that point. Today I'm going to sort through my spring options and order the seal.Thanks for all your help. MUCH APPRECIATED
Have a great day
Ron

[mpbby]

I would talk to the owner about keeping the same spring; good FPS and old times quality.

[Bayman]

I would talk to the owner about keeping the same spring; good FPS and old times quality.

Thanks, I have and it's an option. I'd prefer to refresh the spring with one with zero shot count and would allow room for a better guide design. If not possible I'll work with the factory spring and make the best of it. Both the owner and I'm open to hearing about plausible solutions. I will send back a quiet and smooth gun regardless of the necessary path to it.
Thanks for your input.

[mpbby]

Just to let you know, I had a very bad experience with a Titan spring for my Diana 350.  Although I bought the suggested model for the 350, it simply didn't fit.  With the OEM spring sleeve, impossible.  Even without the sleeve, a VERY bad scratch all way long when cocking. Btw, the FPS was about the same as the OEM springs. Useless.

[Bayman]

Just to let you know, I had a very bad experience with a Titan spring for my Diana 350.  Although I bought the suggested model for the 350, it simply didn't fit.  With the OEM spring sleeve, impossible.  Even without the sleeve, a VERY bad scratch all way long when cocking. Btw, the FPS was about the same as the OEM springs. Useless.

Thank you Marcus, well noted. AoA substituted a titan spring for my Hw30 and it wasn't even close to right. I'm not sure who was at fault there.

On this gun I decided to use a cut to length Vortek spring that's similar in size to the original. I'm gonna have a custom fitted steel guide and a delrin top hat made for it.
Using the factory spring wasn't an option after I seen the pitting and longitudinal wearing on it. I only noticed it today after the wash tank.
Also note the bent OE rolled steel spring guide. I believe that's what was causing all the problems.

[Toxylon]

British airgunners who have tons of experience with their native Titan springs tell that the only thing consistent with the Titan spring measurements is the length. Their fit in particular airgun models is to be considered as mere suggestions. Some springs are too large in OD to fit inside the piston of a gun that it was sold for. Often times a Titan spring works well in a gun that was NOT mentioned in the product info.

That being said, Titan springs shoot hard and are extremely long-lived. By the time a Titan-springed gun starts to show fatigue, you most likely have replaced the OEM or Vortek spring a half-dozen times or more. That's huge in my book, as it's not only the spring cost and the assembly time, but the break-in of a new spring that adds up.

ETA: the fact that the Titan shot about the same as an OEM spring in a 350 Mag is just what is to be expected. The Titan was never sold as a power-booster, and Diana OEM springs shoot hard, anyway. They just don't last near as long.

[Bayman]

British airgunners who have tons of experience with their native Titan springs tell that the only thing consistent with the Titan spring measurements is the length. Their fit in particular airgun models is to be considered as mere suggestions. Some springs are too large in OD to fit inside the piston of a gun that it was sold for. Often times a Titan spring works well in a gun that was NOT mentioned in the product info.

That being said, Titan springs shoot hard and are extremely long-lived. By the time a Titan-springed gun starts to show fatigue, you most likely have replaced the OEM or Vortek spring a half-dozen times or more. That's huge in my book, as it's not only the spring cost and the assembly time, but the break-in of a new spring that adds up.

ETA: the fact that the Titan shot about the same as an OEM spring in a 350 Mag is just what is to be expected. The Titan was never sold as a power-booster, and Diana OEM springs shoot hard, anyway. They just don't last near as long.

Thank you Duke. That's good useful information. It's a shame that the Titan spring sizing is off, because it makes it cost prohibitive for guy like me to try them.

[Bayman]

Hi Ron. I know these guys usually are good for vintage airguns:   https://www.gunspares.co.uk/products/24376/27/  . Maybe also check with Baker Airguns or Precision Pellets?

Good luck in your search!

Also, if ever you had the opportunity/possibility, would you be kind enough to measure the piston stroke on that gun? I have an old chinese break barrel that I think is a clone of the D27, would like to get as much specs as I can for comparison. TIA.

Btw, which trigger does it have?

I measured the stroke its just under 71mm with a synthetic replacement seal. 71 is an odd number I imagine it might be an even 70mm with the original leather seal..

I'm not sure of the trigger designation but it's a three ball design with a metal blade and two adjuster screws. I cleaned, polished and lubed the contact points. Flipped the wear plate and adjusted it. It's a two stage trigger that's heavier, with more second stage travel than my Rekords but it's quite smooth and predictable. It's actually a nice trigger, IMO.

When all is said and done, I think it's a cool little gun.

[jccams]

Do you have it back up and running Ron? 

[Bayman]

Do you have it back up and running Ron?

Yep and running great. I'm shipping it out to the owner tomorrow.

[happymecanic]

Also, if ever you had the opportunity/possibility, would you be kind enough to measure the piston stroke on that gun? I have an old chinese break barrel that I think is a clone of the D27, would like to get as much specs as I can for comparison. TIA.

I measured the stroke its just under 71mm with a synthetic replacement seal. 71 is an odd number I imagine it might be an even 70mm with the original leather seal..

Ron thanks so much! I also installed a synthetic seal in my rifle and I get the same exact stroke measurement. I guess I can now say I have a vintage China-made clone of a Diana 27 lol!

Hope your customer will enjoy this fine piece of an airgun!

Cheers, Francois

[Bayman]

Also, if ever you had the opportunity/possibility, would you be kind enough to measure the piston stroke on that gun? I have an old chinese break barrel that I think is a clone of the D27, would like to get as much specs as I can for comparison. TIA.

I measured the stroke its just under 71mm with a synthetic replacement seal. 71 is an odd number I imagine it might be an even 70mm with the original leather seal..

Ron thanks so much! I also installed a synthetic seal in my rifle and I get the same exact stroke measurement. I guess I can now say I have a vintage China-made clone of a Diana 27 lol!

Hope your customer will enjoy this fine piece of an airgun!

Cheers, Francois

Cheers buddy. I'm glad to be of help.
Be well
Ron

[Bridger3]

Big shout out to Ron for getting my Diana 27 back to me functioning better than when it left the factory. Shot cycle is a thump instead of the twangy self it was. He smoothed the trigger to a light and crisp release. Absolutely great guy to do business with and I really liked how he kept me informed during the rebuild. Thank you Ron!!

[lizzie]

I currently have a Diana27....BEAUTIFUL gun, and great shooter!

[Bayman]

I currently have a Diana27....BEAUTIFUL gun, and great shooter!

Hey Lizzie! How are you? Long time no hear
Text me if you prefer.

Be well ttys
Ron

[lizzie]

Hi Ron! I will text--- sorry it's been so long, I have just been busy with work, because since the pandemic started, staffing has become almost impossible to cover, and I have more work than I want. Haha...

Now that you are delving into Dianas, I have a model 45 that needs a tune, whenever you have the time. Let me know!