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Author Topic: The SSG - What It Is and How It Works  (Read 1810 times)

rsterne

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The SSG - What It Is and How It Works
« on: May 29, 2016, 09:26:28 AM »
The idea behind the "Stopping Spring Guide", or SSG is quite simple.... It is to provide a gap between the hammer spring and the hammer, along with preload on that spring, so that the rebounding hammer cannot recompress the spring when thrown back by the closing valve.... If the hammer spring is recompressed, when it rebounds, it may launch the hammer hard enough to open the valve a second (or third) time, and the air released takes place after the pellet has left the barrel, so it is wasted.... Here is a comparison between four different hammer spring setups, all of which produce the same hammer energy....



This is a generic example, in which the hammer travel during cocking is 1".... If you find the average force exerted by the spring on the hammer, multiplied by the distance the hammer travels while being accelerated by the spring, the result is the hammer energy, in in.lb.... The red line shows a spring with a rate of 15 lb/in, with no load when the hammer is resting against the valve.... It starts off at zero force, and once compressed an inch, the force is 15 lbs., so the average is 7.5 lbs, and the energy is therefore 7.5 in.lb.... The other springs and preloads were chosen to give the same hammer energy, so that the valve should basically react the same....

If you use a lighter spring, at 10 lb/in, you need 2.5 lbs. preload when the valve is closed (and therefore 12.5 lbs when cocked) to get the same hammer energy....If you use a heavier spring, so that you have a 0.1" gap between the hammer and valve stem when uncocked, the spring is only compressed 0.9", so the force when cocked must be almost 17 lbs., which means the spring rate must be 18.5 lb/in.... These are all without an SSG.... Experience has shown us that if you tried these three setups in your gun, you would most likely find that the middle one, with the hammer just touching the valve would be the most prone to bounce and waste air (just like a Newton's Cradle where the balls keep bouncing).... You might be less likely to experience valve bounce with the light spring with preload, but you will notice that the spring is still pushing on the valve even when the valve is open (represented by -0.1" on the horizontal scale), which makes it close slower, and can also waste air.... The short stiff spring will usually be the most efficient of the three, for two reasons....There is a gap that the hammer must cross before it can compress the spring, and friction helps slow it.... and the spring is harder to compress, so the hammer is less likely to store enough energy in it to recross that gap, again slowed by friction, and reopen the valve.... This method has been used successfully to help control hammer bounce for many years.... However, of the three non-SSG methods, it is the hardest to cock, 17 lbs maximum effort, instead of 15 lbs. (medium spring, unloaded), or 12.5 lbs. (light spring, preloaded)....

In many guns, where the cocking effort isn't too high, just use a short stiff spring and you're good to go.... However, in the search for more power, that may make the gun so hard to cock as to be unpleasant, or even cause the action to malfunction.... I use a lot of MRod magazines in my repeater builds, and if the hammer spring is very stiff, the force required to withdraw the bolt far enough to cock the gun rises so quickly that it kind of catches your muscles by surprise, and you may not quite pull the bolt back far enough for the hammer to latch.... When it cycles forward, and then you pull it back again to properly cock the gun, you can double load pellets.... I find that when the cocking effort approaches 20 lbs. I tend to have that problem, so I wanted a solution that would reduce the cocking effort while maintaining enough hammer energy to produce the FPE I want, while not wasting air.... The SSG was the result....

The idea grew from a suggestion by Eric Kuehn (stalwart on the GTA) to use a Gas Ram for a hammer spring, which he calls a GRS.... The intention was to use the fact that a Gas Ram has a preload to overcome (caused by the air pressure inside) before you can compress it, so it is a non-linear device.... The SSG, coupled with a preloaded spring, mimics the characteristics of a Gas Ram.... If you use that with a gap, then you get a spring that has preload, but doesn't push on the hammer when uncocked.... For the last part of the hammer travel it is coasting, and opens the valve from it's own momentum, just like a short stiff spring setup, but with two important differences.... 1. the maximum cocking effort is less.... and 2. for the spring to be recompressed, the rebounding hammer has to exceed the preload.... This is represented by the yellow line on the above graph.... You can see that by using a 0.1" gap, and the light 10 lb/in. spring, we end up with a maximum cocking force of less than 13 lbs, but it takes nearly 4 lbs. of force to start compressing the spring once the 0.1" gap is crossed.... This much more constant spring force.... starting out heavier, but ending lighter, seems to fool your muscles and makes the cocking of the gun feel lighter and smoother as well....

The SSG consists of a spring guide with a stop (usually threaded) installed that keeps the spring under preload....Adjusting the length of the guide adjusts the amount of preload.... A second adjuster, usually in the form of a hollow bolt, allows you to also adjust the gap between the hammer and the valve stem when the gun is uncocked.... I will show some of the variations of this idea in the next post....

Bob


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rsterne

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Re: The SSG - What It Is and How It Works
« Reply #1 on: May 29, 2016, 09:45:26 AM »
Types of SSGs.... with thanks to those who came up with all these variants....















If you have any questions about the SSG, please start a thread for that and I will answer the best I can.... I locked this thread to keep it from becoming cluttered....

Bob
« Last Edit: May 29, 2016, 09:57:50 AM by rsterne »
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