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

[shorty]

I too agree that this topic is about the SSG.

Maybe a new post needs to be started on using the SSG or short stiff spring for efficiency. Apparently most or all of you only experienced <1.5 efficiency and with that being said, new ways of tuning are about to come from it.

Even theories of lift and dwell at lower pressures may change for super high efficiencies that none of us have experienced.

I am still trying to bounce my head around how Lloyds efficiency calculator says that a 100psi drop from 2000psi or 3000psi or 1000psi has the same volume of air used. the only thing that changes is the pressure.

[rsterne]

Lloyd is 100% correct.... The amount of air used (molecules, or volume at NTP) is the volume of the reservoir times the change in pressure....  What you may be having trouble with, is that if you compress a given amount of air to 3000 psi, it takes up only half the space it would at 1500 psi.... so the energy it took you to compress that air is contained in half the volume at the higher pressure.... It follows, therefore, that 1 cc of air at 3000 psi has twice the energy of 1 cc of air at 1500 psi.... However, it has the same amount of energy as 2 cc of air at 1500 psi.... If you expand that 1 cc of air at 3000 psi.... or the 2 cc of air at 1500 psi.... back to 1 atmosphere.... both will occupy the same volume (207 cc).... and both will release the same amount of energy.... In both cases, you would get a 100 psi drop in pressure if you released the air from a 30 cc reservoir....  (29 cc / 30 cc) x 3000 = 2900 psi.... (28 cc / 30 cc) x 1500 = 1400 psi.... (100 psi / 14.5) = 6.9 bar x 30cc = 207 cc....

Actually, once you go above about 3500 psi, and certainly by the time you get to 4500 psi, there is LESS air in that 100 psi change of pressure, due to the Van Der Waals correction, as air no longer acts like an ideal gas as predicted by Boyle's Law.... Conversely, higher pressure air can accelerate a pellet more efficiently, which is why PCPs operating at higher pressure tend to be more efficient.... But again, back to SSGs....

Bob

[shorty]

Yes I do believe lloyds calculator (and yours) is correct. Just hard to wrap the head around it. That's why I mentioned maybe a new post instead of here.

I am not sure the attachment is going to work. Winrar expired on the dumb PC

[wasatch]

Well did another SSG devise today on the TM-1000 FT gun.  This one done having end of stop rod travel down into hammer body when cocked ( removing the kinetic striker & spring using its bore ), floating washer to be the stop shelf, spring support while other end of rod into a fixed base at tension adjuster cap.
NOTHING comes out the rear upon cocking with gun looking and acting 100% stock.   And yes, it works 

That makes all the personal PCP rifles able to be SSG converted done.  Dang what a great devise !!

This sounds really sweet! I think I understand your SSG configuration in the TM1000: does the tension cap adjust preload with the rod adjusting extended length?  What caliber? Is your setup otherwise stock or do you have other springs and different weight hammer?

How much did your shot count or efficiency improve?

I have a 20fpe .177 TM1000 19" barrel with the stock dual hammer springs, stock hammer, inertia weight, etc., reg set at 120bar.  If I were to try your config what spring should I use?  Thanks!

[OZ Harry]

For Bob and any who may have found an interest in my Excalibre hammer mods from 10 years ago; viz in particular the experiments with free travel hammer and short strong home made springs.

This morning I got the old rifle out and stripped it down. It has mostly been used for rabbit extermination these last years as it is my only repeater.

I installed one of the old hammer units ( see the pics Bob posted for me back on page 23 ) which has a very short spring, so there is a lot of ballistic hammer free travel, and just one buffer "O" ring.

Without any other adjustments I shot a short string of 11 shots with JSB 15.9 gr pellets;   then a long string of 49 shots, one plus 6 magazines, with Barracuda 21 gr pellets.

The start pressure in the 203 cc reservoir was 170 bar.
The short string to check things were functioning properly:
15.9 gr JSB Exacts.
11 shots from 790 to 820 fps. 15.9 gr JSB .22s.
2465 to 2305 psi / 170 to 159 bar.
806.27 av fps
22.9 av fpe
1.84 fpe/cuin
8.9 bar-cc/fpe.
15 psi/shot.
Obviously biased by being a short string  in the near side of the climb to velocity plateau.

-------------------------------------
The long string:
21 gr H&N Baracudas,
49 shots from 705.2  to 734.2 to 709.9 fps . That fastest shot was 5.4 fps faster than the next highest.
2465 to 1595 psi / 170 to 110 bar.
719.8 fps av.
24.2 fpe av.
1.60 fpe/cui.
10.3 bar-cc/fpe
18 psi/shot.

The last loctited transfer-port  adjustment I recall as being out 4 turns on the interference screw. I know that that needs to be optimized for best results with this hammer unit so may go back to playing with it again.

Hope some find this of some interest.
Best regards, Harry.
 
 

[rsterne]

Very nice string, Harry, and excellent efficiency.... the first part shows how the HP end of the string is much more efficient, too....

Bob

[Motorhead]

Well did another SSG devise today on the TM-1000 FT gun.  This one done having end of stop rod travel down into hammer body when cocked ( removing the kinetic striker & spring using its bore ), floating washer to be the stop shelf, spring support while other end of rod into a fixed base at tension adjuster cap.
NOTHING comes out the rear upon cocking with gun looking and acting 100% stock.   And yes, it works 

That makes all the personal PCP rifles able to be SSG converted done.  Dang what a great devise !!

This sounds really sweet! I think I understand your SSG configuration in the TM1000: does the tension cap adjust preload with the rod adjusting extended length?  What caliber? Is your setup otherwise stock or do you have other springs and different weight hammer?

How much did your shot count or efficiency improve?

I have a 20fpe .177 TM1000 19" barrel with the stock dual hammer springs, stock hammer, inertia weight, etc., reg set at 120bar.  If I were to try your config what spring should I use?  Thanks!

No picture .... so use your imagination 
But VERY similar to this drawing with proportions quite different in regards to spring/rod & spring depth within hammer. 

* Tho Do Not Agree on No energy being transmitted to hammer & will elaborate that below.

8-32 cap screw with head lathe turned to have clearance within the hammers 8mm kinetic striker bore.
Then made a Peek washer @ .100" thick with clearance hole in middle for the screw above, having an O.D. to be slightly loose within hammer spring bore. ( It rests on the shelf bottom of spring bore with the deep striker bore beneath it )
At the spring tension cap another peek part being a threaded Hat that screw anchors onto, has 2 shoulders to hold primary spring and secondary spring similar to OEM.  The O.D. is that of end cap counter bore.
* Screw is assembled threw washer, then both springs screwed into end hat.  Spring tension gets adjusted initially by varying spring rate of primary spring and length of inner spring to fine tune the tension within @ known OAL specs of the assembled cartridge.
So what you have is a floating spring cartridge affair that drops into the OEM hammer and gets covered by the tension cap that IS NOW USED to set the gap.  Tension is slightly changing OAL of spring cartridge/ changing spring rate & length. Then end cap again sets the gap.

Now as action is cocked the head of screw is allowed to move down the removed striker bore and washer setting on the shoulder of spring bore is now compressed against the spring stack.  Rod is attached to end hat so the assembly stays stationary as hammer is cocked.

Upon firing the hammer is driven forward in typical manor until head of screw contacts washer and the OAL of the SSG spring cartridge is stopped dead !
Hammer is now free floating just before it contact valve poppet in typical SSG fashion 

Reason for using a Peek Washer and Hat was too minimize weight of the spring cartridge, because in this configuration as the head of stop rod impacts the washer stopping spring expansion it sends the spring cartridge assembly forward from the strike  Kinetics 101 ... Lol
Being rear hat is also floating against the rear cap the entire spring cartridge is allowed to move forward or back.
Because we are creating potential for secondary impact or vibration choose to keep the mass and weight of SSG devise at absolute minimums 


Have done this now TWICE, first being with the OEM hammer where it worked but experience told me Dwell was still to much from excess hammer weight just not required.

So ... made a second hammer from Aluminum having a thin anti-wear nylon sleeve on the O.D. and a steel strike pip out front.
Also made it to have @ .300" greater stroke.  Adjusted bores within so SSG would fit without a rod or spring change from OEM hammer.
Weight @ 1/3 that of OEM hammer.   Needed a tad more spring energy but not really that much to get power back.
End result became Very Very similar to my LW hammer marauder tunes with the SSG devises ..... Muzzle report a SHARP SNAP !!
Not had time to run a string ... but so far air use is appearing to be SUBSTANTIALLY less now.  ES #'s are staying +/- 3 fps as well.


** This done on a .177 cal 19 ft lb action w/21" barrel


Regards,
Scott

[aceflier]

So this replaces the hammer spring I take it? Is it still possible to get 60-70FPE out of a .25 Mrod with this? And if so can someone put up some strings doing so? I need to know before I order one from Travis.

Thanks for the help.

[int3man]

So this replaces the hammer spring I take it? Is it still possible to get 60-70FPE out of a .25 Mrod with this? And if so can someone put up some strings doing so? I need to know before I order one from Travis.

Thanks for the help.

Hi just a note.  This increases your shot count / efficiency of the rifle.  If your rifle can't get there now it probably will not after this modification.  To increase FPE you need energy.  This is an air conservation arrangement.  Same FPE with less air.  That said his Spring in this modification, may produce Higher energy than what you currently have, but that is unknown.  Where are you starting?

Drop Travis a line he is good at returning e-mails.  Have any information on your current tune at the ready.

[aceflier]

The rifle is on the way. I'm planning a WAR valve with the 17 lb spring so it should be able to hit that power. But, if this replaces the 17lb spring no point in ordering it and the SSG. I'm looking to maybe get 12 shots at 60fpe vs 8 if the SSG will do it.

[rsterne]

The guy to ask is Travis, since it's his valve and his SSG.... I'm betting he has already tried it.... 8 shots at 60 FPE sounds pretty dismal, I can get that with a modded Disco.... You must be way up on the plateau, trying to wring every last fps out of it....

Bob

[aceflier]

Sorry Bob I should have clarified. I do not have the rifle yet. I Would be happy with 8-10 shots at 60-70fpe. That's why I'm contemplating the SSG. Any more is a bonus. It's going to be used for smaller hogs on my Texas trip as well as fox and coyote around home.

[Blue]

Maybe we could start a few independant threads dedicated to the different "flavors" of the SSG's people are currently building.

This is a great thread and I want to give it a try but I'm not great at getting my brain to translate some of the technical drawings and this thread is a monster to sort back and forth through.

Maybe if we can get a more thorough walk through of steps needed to make them with more pictures or videos it would help me (and others) be able to stop watching on the sidelines and start joining the fun.

I know that the only thing holding me back is not being able to visualize exactly how things look, are made, and work together with more details and step by step instructions for making them at home.

Just a thought, thanks
Blue

[sawtoothscream]

Maybe we could start a few independant threads dedicated to the different "flavors" of the SSG's people are currently building.

This is a great thread and I want to give it a try but I'm not great at getting my brain to translate some of the technical drawings and this thread is a monster to sort back and forth through.

Maybe if we can get a more thorough walk through of steps needed to make them with more pictures or videos it would help me (and others) be able to stop watching on the sidelines and start joining the fun.

I know that the only thing holding me back is not being able to visualize exactly how things look, are made, and work together with more details and step by step instructions for making them at home.

Just a thought, thanks
Blue

I Just want a parts list for a m rod.

[Bullfrog]

The rifle is on the way. I'm planning a WAR valve with the 17 lb spring so it should be able to hit that power. But, if this replaces the 17lb spring no point in ordering it and the SSG. I'm looking to maybe get 12 shots at 60fpe vs 8 if the SSG will do it.

On my .25 Mrod that could do 80fpe easy I couldn't break past 55fpe with the SSG. This is using a 14# spring. The SSG definately benefits from a strong spring. However it doesn't matter to me anymore. On a mostly stock .25 Mrod I got 32 shots at 40 fpe with a tight spread. I wouldn' trade the SSG for more power. The SSG corrects the Mrod's biggest flaw, inefficient air usage. I'd do a WAR valve and an SSG, accept whatever FPE your gun comes out with that gives you a good shot count, and never look back.

[rsterne]

There isn't a lot of room inside a stock MRod, so I can understand why you could find a limit to the FPE you can hit with an SSG without making the gun too hard to cock.... In order to gain all the advantages of eliminating hammer bounce and reducing cocking effort, without power loss, you will need a longer, softer spring, and the SSG will stick out the back of the gun.... That is not to say you have to use an SSG that will pinch your thumb, you may be able to contain it, but you will need a longer end cap to allow for the longer spring.... My Grizzly, which is the first gun I tried with an SSG, is a .30 cal gun and over 100 FPE, for example....

Bob

[Matt15]

Bob,

How does a longer softer spring help gain power compared to a short stiff one?

[Motorhead]

Bob,

How does a longer softer spring help gain power compared to a short stiff one?

A lot of that has to do with getting sufficient pre-load set so bounce can't happen, then have sufficient stroke without incurring coil bind from the heavier wire gauge spring.
Short stiff springs sadly tend to have the lowest stroke potential.

JMO on said Q 

[rsterne]

It doesn't, it allows you to get the same power with a lower maximum cocking force by using more preload.... Three examples using 1" hammer travel.... same average force (10 lbs.).... giving same hammer energy....

No preload, 20 lb/in. spring.... maximum 20 lbs.
5 lbs. preload, 10 lb/in. spring.... maximum 15 lbs.
8 lbs preload, 4 lb/in. spring.... maximum 12 lbs.

If you used the exact same wire size and coil spacing, the 10 lb/in. spring would, however, be twice as long to start with as the 20 lb/in. spring.... You would start with it compressed 1/2", and it would be compressed 1.5" when cocked.... Then it would have to have enough room for all the coils (twice as many) on top of that.... so it needs more space behind the hammer....

Bob

[Bullfrog]

There isn't a lot of room inside a stock MRod, so I can understand why you could find a limit to the FPE you can hit with an SSG without making the gun too hard to cock.... In order to gain all the advantages of eliminating hammer bounce and reducing cocking effort, without power loss, you will need a longer, softer spring, and the SSG will stick out the back of the gun.... That is not to say you have to use an SSG that will pinch your thumb, you may be able to contain it, but you will need a longer end cap to allow for the longer spring.... My Grizzly, which is the first gun I tried with an SSG, is a .30 cal gun and over 100 FPE, for example....

Bob

I may also be using too heavy of a bolt or have too much drag in the SSG's guide. As it stands I can't get enough "umph" to the valve stem without closing the gap too much. When the gap is optimal, I hit a FPE wall that I can only raise by going to a heavier spring. It doesn't bother me though. I'm satisfied with the SSG as it is.

Now on the .177 its a totally different ball game. I can run the gun as powerful as otherwise possible with the factory spring on the SSG. It takes very little power from the hammer to open the valve up to the desired power.