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

[oldpro]

 Ive been playing with bone stock guns but Im about to try it with the NBH then with the NBH and WAR valve. Results very soon. I predict it will flatten out the shot string and maybe add 1-2 more shots.

[Sfttailrdr46]

Ive been playing with bone stock guns but Im about to try it with the NBH then with the NBH and WAR valve. Results very soon. I predict it will flatten out the shot string and maybe add 1-2 more shots.

Will it work with your no bounce hammer?

[Matt15]

Ive been playing with bone stock guns but Im about to try it with the NBH then with the NBH and WAR valve. Results very soon. I predict it will flatten out the shot string and maybe add 1-2 more shots.

Will it work with your no bounce hammer?

NBH= No bounce hammer.  He is about to try it with the NBH. 

[Sfttailrdr46]

  OK, I'll take one of each. I had an unexpected bill today. My avatar needed emergency surgery to remove a bunch of bladder stones so no Flex .30 for a few months. Cosmo just cost me $2,000.00 but he is worth it. I figure a few inexpensive mods for the Gen II Marauder will keep me distracted until my mad money is replenished.

[rkr]

I think the idea with the spring guide mounted on the hammer should work, and as I see it there would be no preload on the valve, because the stop on the guide prevents the spring seat from touching the end cap when uncocked.... It is the exact opposite of the idea proposed by Gippeto, where the guide is fixed to the end cap, and hence takes no energy from the spring.... I'm sure as this idea gets bashed about, there will be even more versions of it.... The original one I proposed does not require a different hammer, although you could certainly change it.... Gippeto, and of course this latest one, both require a different hammer.... All will have advantages and disadvantages, and various degrees of simplicity....

Bob

Hmm, the guide fixed to the hammer would be good when more power and higher dwell time is needed. I don't think it actually needs hammer modifications. The spring and guide move at the same speed as the hammer so you could just attach them with epoxy. It might even work with the spring and guide in free-floating mode as they would still participate in valve impact but most likely stop moving once the hammer has bounced back thus even further reducing the mass moving towards the firing valve after bounce.

Edit, on further consideration the mass of the spring that's not moving entirely will slow down the rod and cause it to impact hammer with a short delay. That may create a "blast tamer effect" killing the rebound or just increase the dwell.

[PBguns]

OK, I'll take one of each. I had an unexpected bill today. My avatar needed emergency surgery to remove a bunch of bladder stones so no Flex .30 for a few months. Cosmo just cost me $2,000.00 but he is worth it. I figure a few inexpensive mods for the Gen II Marauder will keep me distracted until my mad money is replenished.

Speedy recovery pup.

[rsterne]

It is possible the SSG may work with the spring guide completely separate from the hammer and the rear plug.... This would be a method in between Gippeto's and I_like_Irons ideas.... Imagine if you will a spring guide carrying a preloaded spring with nuts on both ends, just sitting between the hammer and the rear cap, with a small gap.... much like a short, stiff spring, but with preload.... For the hammer to rebound and store energy in the spring, it would have to overcome the preload.... The only thing I can see is that you would need a spring with a lot of force, making the gun harder to cock.... and finding enough length could be an issue....

Bob

[Tomg]

Only way I can see it working efficiently is by having the guide being attached to the hammer as described, threaded into the hammer. Then on the backend of the guide there is a hard stop shoulder that have a sliding stop for the spring, so when it is cocked, the hard stop slides through the rear cap, and the sliding stop gets caught by the rear cap compressing it.
Then when it is released the hammer&slide and spring rushes forward towards the valve, the spring gets halted by the sliding stop hitting the shoulder.
The one benefit of this is that there is no ugly nuts or stops on the outside of the rear cap.



The potential problem is that the shoulder would get caught/rub on the rear cap when released. Which could be fixed by making the sliding spring stop almost full sized (hammer OD) and act as a centering device for the guide.





Infact that would work just great I think, as the sliding stop will be pushed against the rear cap until the "gap" is reached and the shoulder meets up with it.

[I_like_Irons]

I've been busy doing some drawing, and I have a Gen 1 Marauder SSG (inverted) designed.  If someone would be so kind and check the dimensioned drawing---these do not have tolerances, yet.

The thing I've designed is adjustable for hammer energy.  It does not affect the maximum cocking force, for that is essentially fixed.  However the hammer stroke is quite adjustable. 

The first drawing shows four states of the system.  Note, the back of the spring guide stays pretty much at the rear support in the end cap. 



By shortening the hammer stroke you reduce the hammer energy.  Consider that the Work (Energy) in the spring is product of the average force and the length.  By shortening the stroke you do two things.  First the length is shorter.  Second the average force goes up.

Consider a 10 pound/inch spring that has an average force of 10 pounds on a 1" stroke.  The pre-load is 5 pounds, the final load is 15 pounds.  This is an energy of 10 in-lbs.   

Now let's take my system and reduce the stroke length to a half inch.  The pre-load now goes up to 10 pounds while the final load stays at 15.  The average force is now (10 lbs + 15 lbs) / 2 = 12.5 lbs.  The stroke is now 1/2".   The equation now is 12.5 lbs x 0.5 in = 6.25 in-lbs.

--------------------------------------------------------------------------------------------

The heart of the system is the Striker Rod.  It's length is fixed and is supposed to have a little bit of clearance between  the end cap stop and face of the valve pin.  This clearance can be adjusted a bit with shims if needed.



The last few parts are in this last drawing.  The e-clip is a standard item.  Note: the washer should have a press fit on the end of the Striker Rod to help transfer force and keep from relying solely on the e-clip. 

[Tomg]

Let me understand this correctly, the striker rod would require enough relief inside the hammer to allow the tip of the striker to be buried inside without touching the hammer at it's resting position? What is moving the hammer upon release, the front spring guide?
That sounds like a lot of very minute clearance "catch you's"

[rsterne]

On quick review, your math looks correct.... My comment would be that I have never understood why anyone would want to shorten the hammer stroke unless they are severely detuning an MRod to work at much lower pressures than can be accomplished by reducing the preload alone.... I have never understood why anyone would choose higher cocking force over longer stroke, but that is what some like to do.... You are correct that by cutting the stroke in half, in your example, you can reduce the hammer energy, but with still 15 lbs. of cocking force, I wonder why you would do that?.... To each his own, I guess.... I use PRod hammers in many of my builds, and the first thing I do is remove the flanged striker, and replace it with a 1/4"-28 setscrew with the end ground flat, and recessed between 1/16"-1/8" in the face of the hammer to increase the stroke.... but I think that your system would work as you say, providing you have the appropriate spring to achieve the energy you need in the space you have availabie with the travel you have adjusted to....

To clarify my post above about the "loose" guide just imagine Gippeto's arrangement, but with the back end of the guide carrying a preload adjusting nut, and butting up against the gap adjusting bolt.... When uncocked, the hammer and guide assembly both rattle around loose, with a slight total gap.... When cocked, the sliding collar on the guide pushes against the back of the hammer, forcing the end of the guide back and then compressing the spring.... The front of the guide slides down inside the hammer (actually the hammer slides back around it).... Sufficient depth inside the hammer is required to allow for the hammer stroke.... In this case, the guide remains still, and only the hammer is accelerated, as in Gippeto's design....

Alternately, you could turn the thing around, and have the stop collar hit the gap adjusting bolt at the back, which is drilled to allow the end of the guide to pass through it and possibly project a short distance behind the head of the bolt when cocked.... Part of the spring length lives inside the hammer.... In this case, the mass of the guide is propelled along with the hammer, just like a free-floating guide captured by the spring works.... and aids in opening the valve, as in I_like_Irons design.... In both cases, there should be no alignment problem with the guide, which can occur when you mount the guide solidly in either the hammer or rear cap.... I can tell you from experience with rear-cockers that if the guide is not perfectly aligned with the hammer, it will hang up in the RVA adjuster it slides through.... In I_like_Irons design, a misalignment of the back end of the guide with the rear cap could cause the hammer to bind, for example....

So, there are a ton of different ways to get to the same result.... Some will work better than others, in certain situations or in certain guns, while others may not be feasible or desireable in those same guns.... I'm just glad to have started the ball rolling so that we can take advantage of using preload in the hammer spring, with a gap between the hammer and valve stem, to eliminate air-wasting hammer bounce....

Bob

[moorepower]

If you can deal with 1/4" O.D. McMaster Carr has aluminum standoffs of various lengths to make a neat looking package.

[Motorhead]

Just finished up an SSG devise for the BSA Scorpion .... same design as M-rods previously.
Utilized a longer 6# spring with heavy preload.  Power easily adjusted to get the JSB 8.4's at 900 fps.
Stupid quiet operation with most noise from hammer spring vibration / strumming.  Need to engineer a fix for that cause it is annoying !

[I_like_Irons]

My comment would be that I have never understood why anyone would want to shorten the hammer stroke unless they are severely detuning an MRod to work at much lower pressures than can be accomplished by reducing the preload alone.... I have never understood why anyone would choose higher cocking force over longer stroke, but that is what some like to do.... You are correct that by cutting the stroke in half, in your example, you can reduce the hammer energy, but with still 15 lbs. of cocking force, I wonder why you would do that?....

To answer your first question, I tune my Marauder and Armada to work with fairly low pressure (150 Bar and 160 Bar respectively).  I do not have facilities to get an SCBA bottle filled anywhere locally.  The lower pressure allows me to get quite a few fills with a SCUBA tank.  Also, the effort to fill with a hand pump is easier as well. 

My desires are not for maximum projectile energies---far from it.  I desire a greater shot count for a fill, along with keeping my pellet velocities at or slightly below Mach 0.8.   In the case of the Armada, I'm trying to duplicate the wind drift (in terms of MOA) at 50 yard with what I get with my highpower competition space-gun at 600 yards.   This .25 rifle does that at about 760 ft/s. 

The example was with the stock spring and the approximate dimensions.  It was purely and example to demonstrate how the change in hammer stroke affects its energy.  I is not necessarily what one would want to do, however.   

The design is intended to be a drop-in and allow one to use any spring that works with an un-modified Gen 1 Marauder, and to allow for additional adjustment as well. 

[rsterne]

If you cannot tune to 150-160 bar with just preload and spring changes, then I can understand reducing the hammer stroke.... I did not mean to offend in any way, there is no right or wrong way to do the SSG.... and I'm glad you got involved and came up with another iteration of the concept that does what you need it to do....

Scott, it's interesting you are now hearing things you could not hear before because of the air not being blown out of the muzzle after Elvis has left the building, isn't it....

Bob

[lloyd-ss]

I have been watching and waiting, hoping that a consensus would be reached on the BEST implementation of the SSG concept. 
I can see that that isn't going to happen. 
What is very exciting is that the concept is so adaptable for applications all the way from max shot count light duty stuff, all the way to high power big bore.     The cooperation and exchange of ideas in this thread is a pleasure to watch. 
Lloyd-ss 

[rsterne]

Yep, Lloyd, pretty much take your pick, there are at least 6 ways to do it now, from what I can see.... *LOL*.... Some need more room than others, ones with more length available can have lighter cocking forces.... Choose one that you think suits your application and have at it....

Bob

[PakProtector]

Got to the materials store; some AL for the guide/indicator and on a whim, some plastic for the end cap nut( Acetron ) from their drops box. At 4" long the guide rod is 5.2 grams running a diameter suitable for 10-32 threading. As soon as I get the nut done, I will cut to length and thread. Springs are dual 1.5" in .059 and .055 wire. The .059 will yield me a combined spring rate of nearly 18 lb/in, and the .055 a rate of 14 lb/in. I dropped the diameter from the OE .480" to .420".

The big valve in the .224 Marauder looks to be *VERY* close to bounce under normal conditions. With the heavy spring now in it, I lubed the tube well with moly grease, and followed with some dry powder. On another gun with a comparable valve I did the same, and after a round of testing I wiped most of the heavier goo out and found it wasted air like a fiend due to bounce. Re-installing the moly goo stopped it to a great extent. I am looking forward to both increasing the power( last max was 103 fpe at 2700 psi ), and gaining some efficiency...as well as some added consistency from lowering hammer drag.
cheers,
Douglas

[oldpro]

 Made a initial run on a bone stock .22 but had about 8 no reads I erased so shot count is a little low. http://airgunguild.com/index.php/topic,11.0.html

[Rallyshark]

Rallyshark.... so a 2-piece hammer ala Daystate "slingshot", only different?.... *LOL*.... With theirs, the outer part hits the valve and stops and in inner section carries on to open the valve.... Either way, you are losing a lot more energy to the part that stops than with the SSG....

bob

I'm not at all familiar with the Daystate setup, since I'm a newb and have very little experience with anything other than my AT-44. I think that sounds kinda neat though.  I wonder how the Daystate would work with the inner section made of tungsten, and the outer of a "lighter" metal?  All of my ideas are pretty much out of me noggin.  I know it would be losing energy, but I was just trying to think of a way to do it and still be able to adjust it, without disassembling the gun.  Maybe, with some materials change, the energy loss could be lessened, but I get what you're saying for sure.  It's not fair that everybody else gets to have an SSG, and I don't,lol!