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

[rsterne]

So that would limit the valve lift to 0.060" minus the SSG gap?.... If you backed out the SSG to adjust the gap to 0.120", the hammer would hit the O-ring before it would hit the valve stem?.... 

Bob

[Tack Driver 10]

So that would limit the valve lift to 0.060" minus the SSG gap?.... If you backed out the SSG to adjust the gap to 0.120", the hammer would hit the O-ring before it would hit the valve stem?.... 

Bob

Right, I keep the free flight small but it all can be modified to fit a particular requirement.

[rsterne]

I get that, but it severely limits the adjustability of the SSG.... ie larger power changes require changing the proportions, rather than just adjusting the gap....

Bob

[Tack Driver 10]

This version has a fixed spring tension, I have an adjustable spring tension version but the knob would be longer.
I wanted this CO2 gun set up for a fixed 10-11 FPE with a short knob.

Here's a version with an adjustable spring tension nut but the trade off is the knob is about 3/4" longer to house the adjustment nut.

[HunterWhite]

Okay,  I  have a question about the gap.

I have built a SSG like the original Bob Stern design in a 2240 co2 pistol, it worked great.

Now I would like to build one with the gap fixed. I have read through hundreds of posts to see if there is an acceptable gap to use. Most posts don't specify,  those that do will be 0.02 to 0.120" (0,5 to 3 mm).
If I just use 0.06(1,5 mm) would this be limiting in any way?

This is for a 20 FPE M-Rod field target rifle.
I have a 30 gram MDS hammer and I have the reg set to 1500 PSI (102 bar).

Hunter

[PikeP]

I agree, its rare to see the ideal gap mentioned. I personally would use 1 - 1.25mm or .04"-.05", which is sufficient for the majority of pcp's to allow two things, the valve to fully close/stabilize, and for some hammer momentum to decay as it has to travel twice that distance prior to striking the valve again.

Increasing gap requires more hammer strike to generate the same FPE as hammer energy/momentum is lost traveling any distance in free flight.

[HunterWhite]

Thanks Matt.
Off to the drill press.

Hunter

[triggertreat]

That's about right on the gap.  The kinda standard when all this started was 0.030", and is what I do.  It's also true, you don't want to fight more cocking force unnecessarily with too much gap.

[HunterWhite]

Thanks Keith.
If this idea works then I guess it will be the seventh type of SSG.

Hunter

[rsterne]

Any gap between 0.030" and 0.125" seems to work just fine.... I have not found problems in testing with much larger gaps, other than you do need more spring force (and get a slightly longer lock time).... However, if the gap is larger than that, you can get differences in hammer velocity shooting uphill or downhill, which is the only real disadvantage....

Bob

[HunterWhite]

Thanks Bob.
I will try 0,040 to 0,050 ( 1 to 1,25 mm).

Hunter

[rsterne]

I usually find a preload that will give me the adjustment range I desire.... If that results in too large a gap, I then reduce the preload on the hammer spring before final tuning.... With many designs of SSG, the gap is easier to adjust than the preload (in many designs that requires removing the SSG from the gun).... If you wish a wide adjustment range, you may have to accept a wider range of gap.... If you are aiming for a single purpose tune, then you can adjust the preload to achieve that at your desired gap.... Too small a gap can waste air because you are still getting some hammer bounce (and often a louder report).... Too large a gap can produced the aforementioned velocity change with gun attitude, and will make the velocity more sensitive to any hammer drag....

Insufficient preload on too stiff a spring can result in increased hammer bounce and cocking effort.... Generally the higher the preload, the lower will be the maximum cocking force, and the greater the resistance to hammer bounce (which is the reason for using an SSG in the first place).... That is why long, soft springs with considerable preload are the preferred choice for an SSG.... Failure to follow that design philosophy is the most frequent reason for shooter giving up on the SSG concept, and any comments you read on them being "too hard to cock".... A properly designed SSG will be easier to cock than any conventional preloaded spring (or indeed SSS), producing the same FPE.... Unfortunately, on some PCPs, there is not enough room to accommodate a longer, softer spring....

Bob

[PikeP]

SSG, TSS, SSS (spring top guide, twin spring system, short stiff spring) all set up in free flight are referred to commonly as hammer de-bounce devices or hammer bounce eliminators, but they don't really eliminate bounce in any sense that serves importance. With a nominal gap, you will still exhibit a successive 2nd and 3rd strike where the effectiveness of your design proves functional or not as to reduce the hammer energy upon those strikes enough to prevent opening the valve...

There is no specific spring rating one must adhere too, but having too 'soft' of a SSG where the spring is easily compressed by the hammer returning to it upon valve closure, is counterproductive. I find having 3-4 lbs of preload minimum on the spring while uncocked is plenty to do the job for most pcps, while some operating at higher pressures with larger poppets may want closer to 5-6. You can achieve this via short stiff springs or long soft springs, what ultimately matters is how its setup when in use. SSG Design, and the rifle its designed for can have limitations to spring length so this shouldn't deter you. As short and stiff are both subjective to a degree, whats short for one setup wont be for another, whats stiff for one person won't be for another...so I like to use the 3-4 lb of preload rule. Easiest way to achieve this is ensure your spring length is a bit under the length allowed on your SSG, to ensure its always under preload. You can achieve this via spacers if necessary or design this feature into the SSG otherwise. I run 1.85" bolts that have a .25" nut/retainer meaning the max installed spring length allowed is 1.6", and I run 2" springs...meaning there will always be .4" preload and at a 7.7 lb spring for me that is 3~ lbs..That spring runs my rifle between 40-65 fpe before being maxed out. My low power 20 fpe tune on the same rifle using a 1.75" 5 lb spring gets roughly .3" preload which is only 1.5 lbs of preload works fine in that low power condition..everything works out merrily with only 1.6" space for a spring to operate...

For comparison here is what it would take to run my valve with a 2.5" compared to the current 2"...not worth the difference.

spring length    spring rating    starting     ending      avg
      2"                     7.7                4.62        10.78       7.7
     2.5"                   6.2                5.27        10.23      7.75

 As stated earlier, only by having the SSG run 'soft' when installed will it lose some effectiveness, which can be done via shorter springs, or longer springs...so ideally you want a spring that's on the lighter side with more preload opposed to a spring that's on the heavier side with zero or minimal once installed and in use. This is because the valve stem has enough energy upon closure, to send the hammer back into the spring and compress it, controlling this via free flight and preload on the spring severely reduces the amount the hammer can re-compress the hammer spring a second or third time.

Proper gap/free flight, and force to compress your SSG (uncocked preload) are primary factors in deciding its effectiveness. How you design around those two factors is entirely up to you.

[Motorhead]

Matt,

  SSG, TSS, SSS (spring top guide, twin spring system, short stiff spring) all set up in free flight are referred to commonly as hammer de-bounce devices or hammer bounce eliminators, but they don't really eliminate bounce in any sense that serves importance. 

Where do you come up with this One statement fits all misinformation ?

A correctly set up SSG with some preload on spring DOES NOT BOUNCE

A TSS or SSS set up I will agree is just a system to control or semi damp the energy created by a bounce.

For the record never been a fan of the latter, but use the former 100 % of the time one can be fitted.

[HunterWhite]

Okay,
This is for M-Rod 20 FPE FT rifle.

It will have Huma regulator set to 1500 PSI (102 bar).

 I have ordered a flat wire spring to use in this mod. It's a Wilson Combat slide recoil spring.  It's rated at 13 pounds, but that's with 4 inches of compression, so that's 3,25 pounds per inch. I will trim the spring if it's too strong.

I have a 35 gram MDS hammer from Rocker1.
It will be about 40 grams with striker and the pin.

There will be preload on the spring stop, but not on the poppit.

I haven't started making chips yet, so I have nothing to show.

Hunter

[Nvreloader]

Hunter

Thanks for the info,
 I'll be following along to see your results using the flat wire spring,
I started using the flat wire springs in my builds, I love the smooth and very easy cocking effort,
and the way the flat wire spring stacks into a very small length as compared to the standard round wire springs etc.

The standard FWspring will compress into about a total length of 1.030" for 5.5"+ OEM length etc.
When first installing the FW spring, use the total full length if possible, then trim length as needed.

I got the hammer out of my Sentry 705 22 cal, I'll be using a Flat wire spring, in place of the OEM round wire spring,
as I have lots of room/distance to play with etc.
The sentry has a power adjuster knob which increases the tension on the hammer spring,
so I'll see how the FW spring works, after I figure out the poundage rating of the OEM spring............

Thanks,
Don

[rsterne]

Scott, I think what PikeP is saying is that the hammer still bounces (it rattles around in the gap), but a properly set up SSG prevents enough energy from being stored in the hammer to reopen the valve.... A TSS or SSS starts with zero preload in order to achieve a gap, and it is easy for the rebounding hammer to compress the spring, which may (or may not) give it enough return energy to reopen the valve....

When I refer to preload in an SSG, I am talking about preload against the stop on the guide.... NOT the valve stem.... That can only occur with an SSG if it is set to zero (or negative) gap, which defeats the whole purpose.... The amount of preload required depends on the hammer mass and travel.... While 3-5 lbs of preload is plenty for a 50 FPE PCP, let me assure you that it is not enough for one producing 500 FPE (unless it has a balanced valve).... The amount of preload is related to the total cocking force required....

Bob

[HunterWhite]

Don, (NvReloader) thank you, I would never have figured out to use slide recoil springs if not for your thread here:

https://www.gatewaytoairguns.org/GTA/index.php?topic=152501.0

Are you using sbrower's method to measure the spring rate?

https://www.gatewaytoairguns.org/GTA/index.php?topic=152501.0

Hunter

[Nvreloader]

Hunter

Thanks, If I can find that tool again, I'll use it on the OEM spring,
there was a spring rating guide all you had to do was enter the info,
and you got a rating of the spring, and I can't find that spring calculator right now............. .

I'll have to set up the hammer and check the spring travel limits etc, and get a FW spring etc,
first I have to deburr and polish everything etc, very rough, crude and sociably unacceptable etc.

Thanks for the info on those posts, saves me spending 1/2 day attempting to find them,
I'll save them, now.

Thanks,
Don

[Motorhead]

Scott, I think what PikeP is saying is that the hammer still bounces (it rattles around in the gap), but a properly set up SSG prevents enough energy from being stored in the hammer to reopen the valve.... A TSS or SSS starts with zero preload in order to achieve a gap, and it is easy for the rebounding hammer to compress the spring, which may (or may not) give it enough return energy to reopen the valve....

When I refer to preload in an SSG, I am talking about preload against the stop on the guide.... NOT the valve stem.... That can only occur with an SSG if it is set to zero (or negative) gap, which defeats the whole purpose.... The amount of preload required depends on the hammer mass and travel.... While 3-5 lbs of preload is plenty for a 50 FPE PCP, let me assure you that it is not enough for one producing 500 FPE (unless it has a balanced valve).... The amount of preload is related to the total cocking force required....

Bob

Bob,
I'm well aware preloading an SSG equipped hammer against the valve stem is counter productive.  Matt and the statement made does not state that but eludes too all three SSG, SSS or TSS don't really eliminate bounce in any sense that serves importance. and that i absolutely do not agree with.  I'm not reading between any lines here .... It is a statement for making HEADLINES of some new unknown story, but is in reality IMO a TROLLING statement.
For those who know better, followed the R&D and used said devices now for several years see right threw this slippery attempt to discredit known cause and effect of reduced hammer bounce devises. Or lacking in knowing the differences of each ignorantly stating there all the same.


I stand by my opinion of this unwavering.


Scott S