A New Method for Increasing the Efficiency of a PCP - the SSG

[SpiralGroove]

Hey guys,
I don't want to sound like a skeptic, because frankly, I don't know . 
But my gut just can't buy an efficiency of 1.94 FPE/CI without the SSG/gun being fined tuned .

That said, I will likely be adding this mod to most of my PCP's .

[oldpro]

Built the first SSG and have it in my personal gun then built the second with specs from first and dropped it in new gun off the shelf. Never touched a thing BUT in my gun it was shooting in the mid 850s so It does need to be tuned to get the power to a more usable speed. The point is that it can be replicated easily and very little tuning needed to get it where it needs to be. Its good to be skeptical I am the biggest skeptic of all believe me.

[rsterne]

I had a good look at the Hatsan.... First of all, there is a 5.5mm hole straight through the middle of the plastic rear plug.... A 7/32" guide rod is a perfect sliding fit, and fits inside the hammer spring as well.... so that could work as a guide.... The trigger assembly JUST clears the hole, so you cannot enlarge the hole to take the spring out the back through the plug.... the trigger is unfortunately in the way.... Any changes to the SSG will require pulling the gun apart and pulling the hammer out the front, OR pushing the trigger pins out, and if you have ever had a Hatsan trigger off, I doubt you want to do that 20 times, you need a special pin to hold the sear in place that you push out when installing the front locating pin.... While I had it all apart, I shortened the top of the safety lever to eliminate the auto safety, which I hated.... I pulled out the hammer preload adjusting screw, and it is 8mm x 1.25 mm pitch, so each turn adjusts the preload 0.0493", call it 50 thou.... The minimum preload is about 1/4", and my 9 turns added 0.45", for the total of 0.70" I measured before.... The small spring spacer with the hole in it is about 0.150" thick (part of that 1/4" of preload), and it, or the spring, won't fit into the threaded portion in the front of the hammer.... There is enough room under where the safety sits to cut away some material from the top of the plastic plug (the part that sticks out above the stock) to allow for the stop nut on the guide, and you could cut a larger slot in the top of the stock (where the slot was needed to miss the hammer adjusting allen key) also.... Therefore, I think the external part of the guide and stop nut, that slides back and forth during cocking, can have a place to live.... under the safety....

My thoughts at the moment are to use a spring guide with the typical peened and shaped nut at the front of spring OD, and threaded at the back for 10-32 nuts, and create the necessary clearance in the back of the plug and stock for them to move during cocking.... The stop nuts will hit the back of the plastic block (with an O-ring cushion), but there will NOT be any adjustment for the gap at the back.... I will try and guess/calculate some combination of spring length and preload that might work, with the original hammer preload adjusting screw all the way forward in the hammer.... I will aim for a bit less preload than I will probably need.... Assuming it turns out that the idea works, but the velocity is low,  I will pull it apart, increase the preload by 0.10", and screw the old hammer screw out 2 turns to compensate, using it as a gap adjuster.... Hopefully I will find a setting that works, if not I will try a stiffer spring and repeat the procedure.... I hope I can get the SSG to work before the gun gets impossible to cock.... I guess we'll see....

Bob

[oldpro]

I was looking at my AT44 to Bob and it looked like a lot of work to be sure but then my squirrel got on the wheel and started running and I think We could build a plug in the back to make a really long rod that went past all the stuff inside and had the SSG bolted to the outside.

[rsterne]

I had the same reaction, first glance I thought no-go.... but now I may have a solution with little work.... The problem is the lack of exterior adjustability, which may require something like you are suggesting.... I know what I want for a tune, and I don't mind taking the gun apart numerous times to get it, but it would not be for everyone....

Bob

[rsterne]

I double checked my measurements, chucked the rear block in the lathe, and using 5/16", 3/8" and 7/16" end mills gradually opened up the recess in the bottom of the overhang of the rear block to miss the 10-32 stop nut.... Here is a photo of it....



You can see that the nut will just clear, and it has about 5/8" or movement available before it will hit he safety button, so it won't interfere, there is even enough room for an O-ring, and in fact you won't even see it.... I haven't carved out the stock yet, but a Dremel will look after that....

Bob

[Rallyshark]

I had a good look at the Hatsan.... First of all, there is a 5.5mm hole straight through the middle of the plastic rear plug.... A 7/32" guide rod is a perfect sliding fit, and fits inside the hammer spring as well.... so that could work as a guide.... The trigger assembly JUST clears the hole, so you cannot enlarge the hole to take the spring out the back through the plug.... the trigger is unfortunately in the way.... Any changes to the SSG will require pulling the gun apart and pulling the hammer out the front, OR pushing the trigger pins out, and if you have ever had a Hatsan trigger off, I doubt you want to do that 20 times, you need a special pin to hold the sear in place that you push out when installing the front locating pin.... While I had it all apart, I shortened the top of the safety lever to eliminate the auto safety, which I hated.... I pulled out the hammer preload adjusting screw, and it is 8mm x 1.25 mm pitch, so each turn adjusts the preload 0.0493", call it 50 thou.... The minimum preload is about 1/4", and my 9 turns added 0.45", for the total of 0.70" I measured before.... The small spring spacer with the hole in it is about 0.150" thick (part of that 1/4" of preload), and it, or the spring, won't fit into the threaded portion in the front of the hammer.... There is enough room under where the safety sits to cut away some material from the top of the plastic plug (the part that sticks out above the stock) to allow for the stop nut on the guide, and you could cut a larger slot in the top of the stock (where the slot was needed to miss the hammer adjusting allen key) also.... Therefore, I think the external part of the guide and stop nut, that slides back and forth during cocking, can have a place to live.... under the safety....

My thoughts at the moment are to use a spring guide with the typical peened and shaped nut at the front of spring OD, and threaded at the back for 10-32 nuts, and create the necessary clearance in the back of the plug and stock for them to move during cocking.... The stop nuts will hit the back of the plastic block (with an O-ring cushion), but there will NOT be any adjustment for the gap at the back.... I will try and guess/calculate some combination of spring length and preload that might work, with the original hammer preload adjusting screw all the way forward in the hammer.... I will aim for a bit less preload than I will probably need.... Assuming it turns out that the idea works, but the velocity is low,  I will pull it apart, increase the preload by 0.10", and screw the old hammer screw out 2 turns to compensate, using it as a gap adjuster.... Hopefully I will find a setting that works, if not I will try a stiffer spring and repeat the procedure.... I hope I can get the SSG to work before the gun gets impossible to cock.... I guess we'll see....

Bob

Thank you guys for humoring me on the AT-44!  I had mind apart as I mentioned earlier.  Like you, I realized that thing uses a lot of pre-load.  My whole "hammer with suspension" idea could possibly work on a gun with a different layout, but it ain't gonna happen on this gun.  I just can't find the room without major modification. 

I did find a very simple solution for it if you're shooting with lower spring settings, like I do with my regulated cylinder though!  I'm not sure what the turns out from minimum it would be on a regular gun, because I added a "stopper" in front of the adjustment screw in the hammer so I wouldn't have to go so many turns in to figure out where I had my spring at.  With that in mind, I have MY adjustment at 1.5 turns out to shoot the JSB 18.1s at 915fps(I'm just guessing that would be 5-6 turns out if it weren't modified).  I looked while it was apart to see how close the hammer was getting to the brass fitting the valve assembly screws into.  The hammer is getting pretty close, it is hitting the stop screw.  In other words the large outer part of the hammer that rides in the trigger tube is getting about the diameter of the stop screw from the face of the brass fitting.  On a quick whim, I took a piece of silicon fuel tube from a nitro rc car and made a loop between the hammer and the brass fitting the air cylinder screws into.  It doesn't interfere with the part of the hammer that actually hits the valve pin.  It isn't a complete loop to allow for the stop screw.  This quietened the gun down, and I looks like it will get me a few more shots by looking at the gauge.  The guns was quieter, and the velocity was only down about 5-10fps, and it appeared that I only used about 30-35 bar on 20 shots.  Normally it would have been down 40-50 bar after 20 shots.  I could be imagining things too   That fuel tubing is about 5-6 mm in diameter and pretty stiff, and it ain't going anywhere, I checked to make sure. 

It made zero difference on the high spring settings with my unregulated "beast mode" cylinder(short), which I didn't really expect it to.  That is when the gun really suks down the air, and where I wanted to see if I could make the real improvements.  I have gotten it to shoot as high as 990fps with the JSB 25s, but that is ultimate air waste for 6-7 loud shots,lol!  I can get about 12-13 shots with a decent ES shooting in the 950fps range, or 15 shots in the 930fps range as it is.  It gets pretty loud when the pressure gets below 150 bar, so I know it is dumping a lot of air at that point.  I know you guys are thinking I need to stop trying to make my .22 a .25, but it is just an exercise in seeing what the gun is capable of   I know the gun is capable of 55+fpe , but it isn't feasible with that kind of air use.  Anything much over 50fpe is just loud and wasting air.  I'm watching your progress like a hawk

[rsterne]

So you are using a rubber buffer between hammer and valve, similar to a bstaley O-ring buffer....

Bob

[Rallyshark]

So you are using a rubber buffer between hammer and valve, similar to a bstaley O-ring buffer....

Bob

Yep, I guess you could say that.  I am not familiar with with the bstanley o-ring buffer?  Remember, I'm a newb I guess the biggest difference is that the fuel tubing is hollow, so it will give more than an o-ring probably.  Does my quick crappy diagram make sense?

[oldpro]

 I had a write up in the euro board on how to mod a AT44 for and adjustable oring buffer mod but not sure how to find it, It has pics and descriptions.

[Rocker1]

     This going to change tuning on airguns by leaps and bounds, will never be the same again imop. Just like Bob says WOW!!!   David

[Motorhead]

At some point in the R&D of the SSG this needs to happen ...

1) Do we need a heavy poppet spring any longer or will a light one allow faster valve opening ?
2) What changes will happen with Heavy to Light hammer weights ?
3) Given spring energy is sufficient to throw weight of hammer used, does a Highly pre-loaded soft spring really operate differently than a stiffer spring with less pre-load ?
4) Does application of a buffer between spring cavity and end of SSG further reduce vibration or bounce ?

This is very exciting but so far in testing appears to be placing PCP valve / hammer tuning of past on the pages of history for many AG designs that can incorporate the mechanics needed to use the SSG devise

[rsterne]

Yep, just like the bstaley mod, except he uses a stack of (usually 3) 70 Durometer (sometime 90D) O-rings.... Search "bstaley mod" and you will find lots of details on how it works and how to tune it.... To really take advantage of it, you need an adjustable length nose on the striker like the MRod or PRod....

Bob

[Gippeto]

You could be very right David...I admit to being more than a little intrigued by the idea.

Spent a little time flushing out my quick sketch...thinking to slab side the striker (two sides), the larger diameter portion of the guide rod and the follower (three sides) to allow air movement. Bushing at rear will adjust via pin spanner, guide rod via hex grub screw. Likely use 3/8-24 and 1/4-28 for threads, maybe inset some nylon beads in threads to provide adjustment stability.

Likely still some fine tuning, but should be close...



Another for the project list, thanks Bob.

Al

[rsterne]

Good questions, Scott, and more research will give more definitive results.... I can give my opinions, based on current data....

1. I would guess that a lighter valve (poppet) spring can be used, particularly in a regulated PCP.... There may still be a case for a heavier one in unregulated ones, because it evens out the total closing force over a wider pressure range.... and in theory can extend the shot string.... The bstaley mod, which effectively acts like a very stiff, progressive valve spring may or may not provide as much benefit, or could work even better, I have no idea.... There is also the possibility that the SSG may extend the shot string of an unregulated PCP over a wider range of pressures, or maybe not, too early to know....

2. My gut feel about hammer weights is that really light ones may not show as much benefit from the SSG, and in fact may not work as well because the guide becomes a larger percentage of the total weight accelerated by the valve.... On the other hand, once the hammer spring is no longer leaning on the hammer during the shot cycle, dwell should decease for a given lift (hammer energy), which is EXACTLY what happens when you use a lighter hammer with a conventional spring setup.... This should result in better efficiency, by using shorter sips of higher pressure (the pressure having less time to decay because of the shorter dwell).... This effect is added to the elimination of hammer bounce, which I think is the main benefit....

3. Good question, and since preload against the hammer DURING the shot cycle is no longer part of the equation, it should be that ONLY the hammer velocity at valve contact (and the hammer weight), and hence the hammer energy, make any difference to velocity and efficiency of the shot cycle itself.... What you do before flinging the hammer at the valve should NOT affect the results.... as there should be no difference in the hammer energy from a given hammer travel if you use a short, stiff spring or a long, weak one.... In theory, it should be the AVERAGE spring force (in lbs.), times the distance (in ft.) the guide moves during acceleration (as FPE = ft.lbs.) that determines the hammer energy.... Preload of zero and cocked force of 20 lbs.... preload of 5 lbs. and cocked force of 15 lbs.... and preload of 8 lbs. and cocked force of 12 lbs.... all have an average force of 10 lbs. and should produce the same hammer velocity, providing the travel distance from sear release to the guide stopping is the same.... Obviously, however, the one with the greater preload and lowest cocking force would be much nicer to cock.... and in the case of a short, stiff spring with zero preload, the SSG may not absorb all the valve closing energy given back to the hammer and you could still get hammer bounce.... Each gun will have a minimum preload requirement to eliminate hammer bounce.... Whether that minimum changes as the pressure drops (and which way) is still undetermined....

4. I haven't a clue if a buffer in the hammer cavity (or as was suggested a fluid camber) makes any difference to the final operation of the SSG.... either good or bad....

Bob

[rsterne]

Al, that looks great!.... Inner thread (on guide rod) sets the preload, and outer thread (on barrel) sets the gap, correct?.... What is the "thermometer shaped" area on the side of the guide?.... and BTW, why should you not get to benefit from yet another project to add to your list.... *LOL*....

I really like the concept that the guide is not moving, and hence not wasting spring energy.... The only wasted energy is on the small ring (follower), and that is tiny.... Do you think the design will require a fairly stiff spring to get enough hammer energy in that length?.... I assume that is a Disco/22XX you have drawn?....

Bob

[Tomg]

Just a small update as I wanted a little more room for a longer spring, so I made the rear cap a little longer.
I have yet to thread the cap so to adjust the preload on the spring. I did however make a flat acetal floating disc so I can use two springs and have them be squared up (I didnt have a long enough spring...)

[rsterne]

You can just butt the springs up against each other, providing the coils are closed up, they won't wind into each other.... no need for the disc (although it won't hurt)....

Bob

[Tomg]

I had to cut one of the springs a little shorter, so it wasn't closed up.....

[Gippeto]

Thanks Bob...all correct as to function.

Used an existing drawing (22xx) to get things to scale and save a little time...thermometer shape is the cutout for striker pin. Spring could be an issue...~5/8" room with striker butted up to tube plug...1.25" at rest but pre-loaded. Will have to see what I have when the time comes. 13/22xx sear spring comes to mind...

Should be able to get more room if needed by drilling the striker through and adding a striker plate to valve stem similar to the BT65. Everything is a trade off hmm?

Al