Diana 56TH .177 - AGT 22mm Skirtless Conversion

[Buldawg76]

Richard
I may be wrong but I believe that the 22mm kit would indeed lesson the cocking effort of your 54 a considerable bit. The 48.52.54.56 platform guns are generally considered magnum level guns so hence the heavy cocking effort associated with them. I do know when I detuned my /177 D48 from shooting close to 900fps with 8.44 pellets down to just under 12fpe/790fps it made a huge difference in the cocking effort required. The fact that the 22mm kit makes more pressure with the reduced swept volume it does not require as much spring energy to perform the same task which means less cocking effort for the same power.

Mike

[Yogi]

Seems some folks need a few more in depth answers, so i will tell you a a story.

Around 6 years ago, maybe 7 i converted a HW77k from 26mm to 23mm, this was the first gun i reduced the piston size on, why 23? well i could easy buy at that time 26mm OD and 23mmID tube, so 23mm was easy, plus i wanted to keep the 9 25mm comp tubes i had all 25mm at that time . So I experimented a while, playing with piston weights, inertia weights, seals, etc but never stroke, at that time the pistons weighed around 175g and ran stock HW77 stroke. I also at that time started working out the efficiency of the power plants, how much energy in was converted into energy at the muzzle, this was a big eye opener. Now some of you have seen i was featured in a magazine, i actually dont like that article, its not what i was expecting to come out, falls way short of explaining why smaller is better and basically just says its all my opinion and i think it works...but at least it got peoples juices flowing about smaller might be better. Around this time i was approached to build a 23mm TX, now i had sold mk3 HC a few years earlier so i explained i did not have one to experiment on so would not like to mess the a customers gun if it did not work, i was offered a TX 177 rifle at trade price right there and told dont worry, if it does not work we can always buy the spares and put it back to stock

So TX rifle, no decent small seals on the market, only real option was O rings, i set too, soon realized i needed to run near full mk3 stroke to make the efficiency high etc, which had me puzzled as the 77k always ran much shorter stroke. So i started building the bronze nose O ring 22mm conversions and a few folks jumped on the train wanting one also, i actually made around 35 of these. Around this time i decided to revisit piston seals, approached 5 seal manufacturers who basically knocked me back, refused to work with me as they work with competitors already, but then 1 called me back..and agreed as it would be a challenge to have a go with me and the seal journey started. Within a few weeks i had prototype 22mm seals and again my eyes were ripped wide open, the power plants converted from O rings to seals were making in some cases 80fps more velocity, this is where the stroke changes started. I basically reworked a TX so i had a rod i could adjust the stroke with very easy and lock it, i tested from 98mm down to 80mm in 1mm steps, keeping preload the same so the same input energy, then i tested different springs (wire thickness so higher rate), different spring lengths...you name it i did it, 3 months solid testing. Out of this came a formula, i found i can apply this formula to any under lever or side lever rifle regardless of whether its a mk1 2 or 3, Diana, AA, HW, Umarex, they are all just a chassis that needs a specific power plant to work well and pretty much the same formula works for all. There are some exceptions, the LGU does not make power easy in 22mm form, its like the LGU was designed to not perform well, my LGU is long stroked to 92mm, it is 22mm, and it does perform, but its hard to get every 177 LGU to do as well, .22 is not an issue however, 22mm LGU in .22 is easy and a beautiful thing to shoot.
So, Steve has already explained if you have a Mk2 TX i change the rod to a mk3, the gun is long stroked and converted to 22mm, the same stroke is run on a mk3 or a mk1, the chassis is just converted to my spec for stroke, they all come out the same.

So Diana's i have converted to 22mm or 20mm (yes i run 20mm pistons also)

2x440TH, (430) long stroked, need a fulcrum change to sort the cocking effort which I will do and offer.
2x 470TH   Shorter stroke, cocks like a 77k, beautiful gun but heavy, the 430 with fulcrum change will be as good.
4x 52's in .22 and 177, 3 in 22mm one 177 in 20mm, this runs full 105mm stroke presently on an o ring soon to be seal tested.
1x34 24mm conversion, glued in sleeve, LGU piston with revised seal and bearings (my own seal machined down to 24mm)
Working on a Diana 75 conversion, too what? I have no clue yet ;-)

So out of this you should have guessed i apply a forumla to all guns, whether Diana, AirArms, HW, Umarex, mk1 2 or 3, does not matter, its just a chassis and i build in what I know works

TonyL-

Why does this formula only work on side and under levers? 
As you can tell from my gun list. I am a big fan of the HW 50 or 99 in the UK.  It has always puzzled me why people talk about the old HW 50, which had a 25mm comp. tube, in such glowing terms.  Seems to be even smoother than the pretty smooth newer HW 50's with a 26mm comp tube. 
Who knew a "silly little mm" made such a difference?

-Y

[Yogi]

I do really appreciate the sharing of knowledge from all fellow GTA members since for me its the one thing in life that no one can ever take away from you .

Mike

Agreed, but my mother often said, "i'll remember this the rest of my life".  Towards the end, this was no longer true!

-Y

[Artie]

Yogi, take another look at the bottom of TL's response you quoted. A D34 is on the list.

[Yogi]

Yogi, take another look at the bottom of TL's response you quoted. A D34 is on the list.

Richard,

My comment was aimed at this statement:
" Out of this came a formula, i found i can apply this formula to any under lever or side lever rifle regardless of whether its a mk1 2 or 3, Diana, AA, HW, Umarex, they are all just a chassis that needs a specific power plant to work well and pretty much the same formula works for all."

Good catch that he has "done" a break barrel.    I am assuming that this is what caused the comment that the formula only works on on side and under wankers.

-Y

[Buldawg76]

I do really appreciate the sharing of knowledge from all fellow GTA members since for me its the one thing in life that no one can ever take away from you .

Mike

Agreed, but my mother often said, "i'll remember this the rest of my life".  Towards the end, this was no longer true!

-Y

Yogi

The key here is that no ONE ( person ) took that away, God was who took that away only he did not actually take it away rather just made it harder to remember or find in her mind

Mike

[Yogi]

I do really appreciate the sharing of knowledge from all fellow GTA members since for me its the one thing in life that no one can ever take away from you .

Mike

Agreed, but my mother often said, "i'll remember this the rest of my life".  Towards the end, this was no longer true!

-Y

Yogi

The key here is that no ONE ( person ) took that away, God was who took that away only he did not actually take it away rather just made it harder to remember or find in her mind

Mike

Mike,

Is that kind of like you can't unsee something!

I certainly agree that GTA is a wonderful source of information with a bunch of people who really try to help.

-Y

[Buldawg76]

I do really appreciate the sharing of knowledge from all fellow GTA members since for me its the one thing in life that no one can ever take away from you .

Mike

Agreed, but my mother often said, "i'll remember this the rest of my life".  Towards the end, this was no longer true!

-Y

Yogi

The key here is that no ONE ( person ) took that away, God was who took that away only he did not actually take it away rather just made it harder to remember or find in her mind

Mike

Mike,

Is that kind of like you can't unsee something!

I certainly agree that GTA is a wonderful source of information with a bunch of people who really try to help.

-Y

Yep Yogi

I would agree that is a Sooo very accurate statement.

Mike

[triggerfest]

A piece of art again Steve ! I bet you will enjoy the T06 trigger over time.

Regarding your pellet choice, typically Diana's are doing great with RWS pellets. Especially the RWS Superdomes are superb, you might want to give those a try as well.

[TonyL]

Thanks for pinpointing that  aspect of the discussion to me Mike, I completely missed it.
I am now cautiously building hope for my .22 D54. The only reason I don't shoot it more often is it is becoming increasingly more difficult to target shoot  for more than 20-30 shots due to the cocking effort. Am I correct to believe the 22mm conversion would lessen cocking effort or is my assumption misguided?

yep would be a lot easier to cock

[TonyL]

A while back i took a liking to Diana 280's, i have now moved to the 34, running 24mm conversion and 90mm stroke its utterly stunning at a little over 11fpe in 177, almost as good as one of my 22mm TX's

[Mossonarock]

Steve,

I'm wondering how you polished the insides of the slide blocks.
I took a close look at mine and I'm a bit surprised at how rough some of the metal is.
I can see why polishing it all up would smooth out the sliding mechanism.
I just hope that polishing it up doesn't introduce excessive play.

[Nitrocrushr]

Steve,

I'm wondering how you polished the insides of the slide blocks.
I took a close look at mine and I'm a bit surprised at how rough some of the metal is.
I can see why polishing it all up would smooth out the sliding mechanism.
I just hope that polishing it up doesn't introduce excessive play.

I simply used a bore mop, .22 caliber I think

https://shop.brownells.com/gun-cleaning/patches-mops/bore-mops/wool-bore-mops-prod25917.aspx

I chucked in my cordless drill, smothered in Mothers aluminum polish and gently spun it up while working in and out.  Then a clean mop spun up to finish it off.  In no way was it aggressive and smoothed it up nicely without creating any loose fit.

[blackdiesel]

You guys are making it hard for me to enjoy my "straight from the factory" D56s 

[Nitrocrushr]

You guys are making it hard for me to enjoy my "straight from the factory" D56s 

I picked up a brand new D56 this week.  I took it straight from the box and put about 75 shots through it.  I then picked up my D56 22mm, what a difference The smoothness of the cocking action and softness of shot is amazing😎 After shooting the 22mm for awhile I forgot how much of a difference there was til I shot this new one.

[blackdiesel]

You guys are making it hard for me to enjoy my "straight from the factory" D56s 

I picked up a brand new D56 this week.  I took it straight from the box and put about 75 shots through it.  I then picked up my D56 22mm, what a difference The smoothness of the cocking action and softness of shot is amazing😎 After shooting the 22mm for awhile I forgot how much of a difference there was til I shot this new one.

I'm mostly a PCP guy, but I like Dianas.  I have no skills in working on or modifying springers so I will just have to be happy with my stock springers.

[WHITEFANG]

Got to say this topic was some fine reading.
Plus some super mods. Very impressive work and results.
Super Sweettttt gun💀

[subscriber]

And, since F=m*a, and W=E=F*d, there are a MULTITUDE of binomials (spring rate*stroke & mass; which by the way are themselves products of several factors) that will achieve the same acceleration and will generate the same Work/Energy, so just changing ONE variable is not enough to convince me.

I realize that I am late to this party, but allow me to share my insight:

I agree that the potential and kinetic energy in the spring and piston are finite quantities, and the rule of not getting something for nothing stands.  My understanding is that what the skirtless piston concept looses in the spring's input energy is made up for by its vastly improved efficiency, when transferring that energy to the pellet.

This efficiency improvement stems from the very fast piston motion: The light piston enables very rapid acceleration at lower spring force.  Its smaller piston area enable it to generate not only very high pressure, but more importantly, very high temperature.  The higher temperature air has a larger effective volume (as does hot propellant gas in a firearm barrel), for just long enough to accelerate the pellet to useful velocities early in its travel, before the air has time to cool significantly.

Piston bounce is a function of piston mass to area ratio.  Reducing the piston mass will not increase bounce, if the piston area is reduced by the same or greater proportion.  A 20 mm diameter skirtless piston may bounce less than a regular 26 mm version, driven by the same spring.


Simple illustration of time dependent air compression energy transfer:




I am waiting for some luer fittings to arrive, so I can join two identical 10 ml syringes neck to neck (mocked up in attached image).  I want to use these "cylinders" to demonstrate the time dependency of energy transfer efficiency in air compression, as it relates to compression rates and the resultant temperature rise rates. 

Principle:
When the fully extended plunger "A" is moved slowly to position "C", plunger "B" will at most assume position "D" (less because of friction at the seal).  This is because the pressure increase, before the receiving piston starts moving is low, and because the very modest heat generated by that compression, has time to escape. 

However, if plunger "A" is compressed vigorously, like slapping a "fire piston" to position "C", the pressure increases rapidly to a more significant level.  That rapid pressure rise in the driving cylinder will result in a significant increase in the air's temperature.  This raises the air's effective volume beyond that of the matching cylinder, receiving the heated air.  Thus,  plunger "B" will fly out of the receiving cylinder well beyond position "D".

The faster such compression is achieved, the more thermal energy would be transferred to the receiving plunger; or in the case of the skirtless piston air rifle; the pellet.  This is my understanding of what makes the smaller diameter, lighter piston work, despite its reduced swept volume and modest spring energy.

Until I can confirm the above syringe plunger projection principle (sure I have done this in my inkjet printer engineering days), this video is a convincing demonstration of heat of rapid air compression.  Just imagine that scaled up and driven faster by means of a spring:

[Buldawg76]

Yep the difference is approx. 1200 psi for a conventional piston diameter versus 1800 psi for a 22mm piston.

BD

[Nitrocrushr]

And, since F=m*a, and W=E=F*d, there are a MULTITUDE of binomials (spring rate*stroke & mass; which by the way are themselves products of several factors) that will achieve the same acceleration and will generate the same Work/Energy, so just changing ONE variable is not enough to convince me.

I realize that I am late to this party, but allow me to share my insight:

I agree that the potential and kinetic energy in the spring and piston are finite quantities, and the rule of not getting something for nothing stands.  My understanding is that what the skirtless piston concept looses in the spring's input energy is made up for by its vastly improved efficiency, when transferring that energy to the pellet.

This efficiency improvement stems from the very fast piston motion: The light piston enables very rapid acceleration at lower spring force.  Its smaller piston area enable it to generate not only very high pressure, but more importantly, very high temperature.  The higher temperature air has a larger effective volume (as does hot propellant gas in a firearm barrel), for just long enough to accelerate the pellet to useful velocities early in its travel, before the air has time to cool significantly.

Piston bounce is a function of piston mass to area ratio.  Reducing the piston mass will not increase bounce, if the piston area is reduced by the same or greater proportion.  A 20 mm diameter skirtless piston may bounce less than a regular 26 mm version, driven by the same spring.


Simple illustration of time dependent air compression energy transfer:




I am waiting for some luer fittings to arrive, so I can join two identical 10 ml syringes neck to neck (mocked up in attached image).  I want to use these "cylinders" to demonstrate the time dependency of energy transfer efficiency in air compression, as it relates to compression rates and the resultant temperature rise rates. 

Principle:
When the fully extended plunger "A" is moved slowly to position "C", plunger "B" will at most assume position "D" (less because of friction at the seal).  This is because the pressure increase, before the receiving piston starts moving is low, and because the very modest heat generated by that compression, has time to escape. 

However, if plunger "A" is compressed vigorously, like slapping a "fire piston" to position "C", the pressure increases rapidly to a more significant level.  That rapid pressure rise in the driving cylinder will result in a significant increase in the air's temperature.  This raises the air's effective volume beyond that of the matching cylinder, receiving the heated air.  Thus,  plunger "B" will fly out of the receiving cylinder well beyond position "D".

The faster such compression is achieved, the more thermal energy would be transferred to the receiving plunger; or in the case of the skirtless piston air rifle; the pellet.  This is my understanding of what makes the smaller diameter, lighter piston work, despite its reduced swept volume and modest spring energy.

Until I can confirm the above syringe plunger projection principle (sure I have done this in my inkjet printer engineering days), this video is a convincing demonstration of heat of rapid air compression.  Just imagine that scaled up and driven faster by means of a spring:

Very interesting!!!! Thanks for posting and I look forward to hearing more as you begin your experiments with the syringes.  It would be interesting to see both small diameter and slightly larger diameter syringes being compressed into a common sized syringe with a quick motion compression as in your video link.

Steve