Hammer Stop in a Regulated PCP ?

I have been thinking about regulated guns using a hammer stop for a while, and the idea intrigues me.... I'm not sure if it would be better to use a rigid stop (Delrin?) or O-ring(s), but I'm leaning towards the O-ring(s).... or possibly an energy absorbing polymer that could prevent hammer bounce.... The concept is this: In a regulated gun, if you have too much hammer strike, you get too much lift, and you waste air, without adding any velocity.... You can actually push the dwell to the point where "Elvis has left the building" and the valve is still open.... If you plot velocity vs hammer spring preload you will get a graph like this....

http://i378.photobucket.com/albums/o...Efficiency.jpg

You will note that from coil bound to 3 turns out, the velocity doesn't change, but the amount of air used drops by 50%.... Obviously, operating in this range makes NO sense at all.... As you continue to reduce the hammer spring preload, the velocity starts to drop a bit (maybe 30 fps by 4 turns out), but the gun continues to use less air, in this case 25% less air for only 3% less velocity.... That is where I would usually run this gun, and not just because of the excellent balance between power and efficiency.... At that point (on the "knee" of the curve) you are actually operating right near what would be the peak of the "sweet spot" in an unregulated PCP.... That means you can actually shoot somewhat below the regulator setpoint before the velocity starts to drop.... In this case, you could probably shoot down to 1300-1400 psi (the setpoint is 1600) and still only be down about 1% in velocity.... At preload settings up on the plateau, once you hit the setpoint, the velocity drops like a stone by comparison....

An interesting thing happens when we reduce the preload further.... The velocity continues to drop, and the efficiency continues to increase, both good things.... However, once you reach the setpoint on the regulator, the velocity will begin to RISE before falling off.... This is because the gun is operating like a conventional PCP but with the top of the velocity curve flattened by the regulator.... Here is an example (with compressed "x" axis while on reg.) showing what can happen when you operate in that mode....

http://i378.photobucket.com/albums/o...QBLowPower.jpg

On the left side, above 1400 psi, the gun is operating in regulated mode, and the velocity for the first 70 shots is pretty constant.... Once the pressure drops below the setpoint, however, over the next 30 shots the velocity INCREASES nearly 150 fps, peaking at about 1000 psi, before it starts to drop again.... That is because below 1400 psi the gun is acting as a conventional, unregulated PCP.... It is in THIS mode of operation where I see the hammer stop as being the most valuable.... If, instead of using hammer spring preload to set the lift (and hence the velocity), we used a positive hammer stop.... we should be able to eliminate that "bump" in the velocity curve below the setpoint, because the lift could no longer increase as the pressure dropped.... Instead of the velocity increasing, with the lift limited, the velocity should decrease as the pressure declined.... This could be particularly useful where there is a "legal limit" on the velocity or energy, either by law, or by rules such as in Field Target.... You could set the gun up to be "legal" above the setpoint, and not have to worry about the velocity climbing below that.... If we used a rigid stop (or an energy absorbing one), the velocity should decline immediately after it came into contact as the pressure dropped further.... That could still be set for maybe 100 psi below the setpoint.... If we used an O-ring buffer, it may be possible to create a shallow curve (ie much as what occurs when you operate on the "knee" of the preload curve) that extends the shot string 200 psi below the setpoint....

You may ask "why not just lower the setpoint" to operate at reduced velocity, and then move back to the "knee" of the (now lower velocity) curve.... That is certainly a very good way to tune the gun, always keeping the setpoint pressure and the hammer spring preload "in balance".... However, the efficiency (but not necessarily the shot count) will tend to be higher if you run a higher regulated pressure and then reduce the preload so that you are operating on the "downslope" on the right hand side of the curve.... The reason for that is that you are using a smaller "sip" of higher pressure air the whole time you are above the setpoint.... Using a hammer stop to prevent the rise in velocity below the setpoint in conjunction with that tune could well prove the best choice.... The reason I said this MAY not result in the largest shot count is that lowering the setpoint increases the amount of air you can use from the tank.... and then operating on the "knee" of the curve increases that even further.... Therefore "knee" tuning may results in the most shots, but with lower efficiency.... I have to admit I don't have the data either way, and it is likely each gun may be different anyway....

Now, let's look at how we might use this hammer stop idea INSTEAD of preload adjustment to set the velocity.... Let's say we set the preload at 2 turns out, so that we were well up on the plateau of the curve.... and let's assume we install a bumper made of a polymer that is designed to have energy absorbing properties.... The first advantage I can imagine is that the possibility of hammer bounce should be reduced as any extra hammer energy/momentum won't go into additional valve lift, and hence stored energy available to throw the hammer backwards.... Instead of reducing the preload to lower the velocity and increase the efficiency, we back off the striker in the face of the hammer to physically reduce the valve lift.... Imagine that you are recessing the face of the hammer, so that when the hammer hits the bumper, the valve stem isn't pushed as far.... Less lift means less velocity, and less air used.... We move to the right along the velocity curve, and I would suggest that the curve would be virtually the same shape, having a "knee" and then a declining slope.... I would further suggest, that other than a reduction in hammer bounce (which could increase the efficiency), that the efficiency curve would also be similar.... Ths difference I perceive is that when you are well down on the "downslope" on the right of the curve, there would no longer be an upwards "bump" in the velocity curve when the pressure dropped below the regulator setpoint.... as the lift could no longer increase because the hammer is already hitting the bumper.... The only downside I can see is that "knee" tuning which can extend the shot string below the setpoint 200-300 psi would likely not occur, as the lift can't increase as the pressure falls below the setpoint.... However, if hammer bounce was reduced, that could (maybe) make up for the missing shots....

So, who's going to be the first to try it?.... I wish I had the time right now, as I'm pretty excited by this concept....

Bob