Tuning Titan spring/Diana 460 experiment - predictions wanted

Long post, so to jump right to the "Big Question", just skip to the end...

The backstory...

I have a refurb Diana 460 that was definitely NOT refurbed. After a friend dug chunks and sheets of flattened pellets out of the workings it was shooting pretty well with what I think was an OEM spring (spring dimensions below). It made 20/21 fpe in .22 but the spring had lost its straightness and would drag quite a bit during the cocking stroke, so I went in search of a replacement.

I bought an ARH "full power" spring that was overlong and produced only 16fpe. The ARH spring is as straight as an arrow and cocks cleanly, but clearly it is too much spring for a 460 at 11.75 inches (new). FYI, the ARH was .1265" (.002 smaller) wire, with nearly the same ID & OD. But only 30 coils (ARH) vs 32 and nearly 1 inch longer (10.9 long refurb spring).
Rather than clip a coil or two, I decided to preserve that spring as-is and try another spring, now that I had measurements. After all, life is an adventure!
So I rolled the dice with a pair of Titans - a #1 and a #8. They just came in today and I took some measurements, to see what I had actually received, 'cause I've heard some stories.... 😁
The #1 that I feared would be a little short at a reported 30 coils/280mm actually measures 286mm (30 coils) and may be a good length without any spacing.

The only catch is - its 30 coils for the Titan #1 vs 32 for the "refurb" spring. I don't know what performance characteristics those 2 fewer coils represent, though I'm guessing it should be "springier" yet a little less powerful. Could result in a softer cocking but still 20fpe rifle. At least, that's what I'm hoping.


The #8 is 34 coils and 11.75 long, and would only be good for a 460 if shortened I think, so it will be put aside for another rifle.

BTW, the ends of both Titans aren't ground anything like square, so I'm going to have to do that. They're pretty lousy in my opinion, for whatever that's worth.


The Big Question:
How will my rifle most likely respond to the switch? That's what I'm asking for predictions on.
It will probably take a little while for me to get the new spring switched in, so you all have a little time to mull it over if you like.


The numbers:

"Refurb" spring:
32 coils, Wire Dia. 126/.1265 coil gap approx .215 (calculated)
ID .566x.570
OD .823/.829
OAL 10.9" (used)


Titan #1
30 coils, wire Dia .1275/.1280, coil gap .243
ID .570/.573.
OD .834 / .840
OAL 11.25" (new)

FYI, its worth mentioning that the piston and transfer port seals were replaced and the rear of the piston was buttoned earlier. That's how the rifle was set up when it was producing 20-21 fpe after it was made right by my friend. The rifle has probably only seen 50 or 60 shots after that happened.
 
Hold over, you may well be right. I made up some shims this week, each around .150 thick, that match the spring's diameters in case I feel that a little preload would be beneficial.
I'd prefer to go without them though. Even if they are new and shiny... 😁
I will be interested in your results. Would also be interested in test results from the other spring at 34 coils if it would fit in there.
 
The Titan #8 is awfully close in size to the ARH spring. It should fit, but would likely be just as oversprung if not more. I think that both could be excellent springs for the 460 if they lost a coil or two.

Here are the numbers for each:

ARH Full Power spring for D460:
11.75" long 30 coils Wire dia .1285"
OD .815 ID .556 to .560

Titan #8
OAL 11 3/4 34 coils Wire Dia. .128"
OD .812 ID .543 to .548

The Titan has nearly 1/2" less room before it becomes coil bound, so that is certainly a potential issue.
Also, Hector mentioned somewhere that Diana guides are typically right around .543, which matches up nicely with the #8.
 
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It made 20/21 fpe in .22 but the spring had lost its straightness and would drag quite a bit during the cocking stroke, so I went in search of a replacement.

I bought an ARH "full power" spring that was overlong and produced only 16fpe. The ARH spring is as straight as an arrow and cocks cleanly, but clearly it is too much spring for a 460 at 11.75 inches (new). FYI, the ARH was .1265" (.002 smaller) wire, with nearly the same ID & OD. But only 30 coils (ARH) vs 32 and nearly 1 inch longer (10.9 long refurb spring).
I don't understand. If the gun only made 16 fpe with the ARH spring, how is it "too much spring"?
 
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It has a little thicker wire, but more coils and is quite a bit longer and that made for a lot of preload. I believe this is a good example of an over sprung rifle.
I'm not sure that I truly understand it myself, but my limited experience with springs in general has me thinking that the spring can't extend far enough for that rifle/compression chamber stroke to get the full benefit of the spring's extension action.
I imagine that both too little preload and too much preload are both detrimental to power output.

Please do NOT take my musings as any kind of fact.
When it comes to springs, I'm still learning which questions to ask. I don't have the answers.

I will probably leave my 460 cocked for an hour or two before I pull the spring, to see if that has an effect.
 
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OK - I averaged the following after maybe 50 pellets immediately after the change to the ARH spring then about 9 months of non use:

Spring "unset" - shots taken at 2:45pm (14.0 Mkgln)
1. 740.4
2. 731.8
3. 715.6. Felt loose/discarded
4. 734.8
5. 727.6
6. 727.8
AVG = 732.48 fps (16.67 fpe)

It seems like that first shot was a little optimistic, but still fairly consistent.

I left the rifle cocked (unloaded) and I'll take 5 or 10 more shots at 8pm tonight, to see what affect the 5 hours has on it.

I'm having fun with this little experiment.
FYI - yes, I understand that what I'm doing isn't really a true set (full compression over a snug mandrel).
 
Most of the JM stuff runs alot of preload. Overall length doesn't matter as long as the spring has adequate preload and doesn't coil bind. As long as the outside diameter of the JM spring is close with more coils and heavier wire it should be stouter. Why it would lose 4 fpe confuses me if there's been no other changes. Sure you can overspring a gun and actually lose some power, but that's a lot of lost power. Is the spring tight on a guide?
 
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Here's what I can say: ID's of those two springs were pretty close, but neither was a tight fit on the guide. And the power dropped instantly when we swapped springs. And we did not move the piston. Between that and the consistent velocities it produces, I am confident we didn't damage the piston seal.

I'll be more careful about taking notes when the ARH spring gets swapped out in favor of the Titan.
 
OK, the little side experiment turned out as expected - lost a little velocity after leaving it.cocked for 4 hours. The new numbers:

1. 710.6
2. 694.8
3. 710.6 again
4. 711.2
5. 711.3
6. 702.7

15.66 fpe

Used 14.0 Meisterkugeln for both tests above. Difference = 1 fpe

Also tried:
Norma 17.6 Domed

1. 591.9
2. 592.3
3. 572.4 (felt looser than the others)
4. 589.7
5. 577.1

13.6 fpe


Excite Hammer Dome Much better fit!

1. 690.3
2. 681.5
3. 680.5
4. 681.6
5. 681.6 again
6. 678.9
7. 670.7 pellet prob a little extra snug
8. 687.9
9. 674.8
10 678.2

15 fpe

Weighed 5 Hammer's: 14.64, 14.68, 14.68, 14.67, 14.63 grains


AA 15.9 domed
664 and 665 for 2 shots
 
It has a material selection.
I had about 10 free minutes at work today so I punched in the numbers for all 4 springs, and made a word document with the results.
Didn't read it yet, and forgot to print it too.
I'll get it tomorrow when I pick up my springs. I dressed the ends (they were far from square) and forgot those on my desk too when I ran out the door. Doh!
 
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OK, finally got a chance to post these pics for anyone who's curious....
I'd like to double check the coil count etc. on the OEM spring just to be sure of them, but I don't remember where I stashed it. It should be correct though. I can double check the ARH when it comes out of the 460. The Titan numbers are on the money.

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