I would definately think the tension of the spring has an effect on velocity/effiency and the pressure in which the gun CAN operate at. Now the weight of the bolt is a different story.
First of all, we all know that a mag has a dump chamber pressure of about 400psi. We also know that there is roughly 60-80psi of air launching the ball out the barrel. Now tell me where the other 320-340psi goes....most of it must be used to push the bolt forward against the spring.
These are just thoughts here and have no fact behind them. It would seem that a weaker bolt spring would take less pressure to push the bolt forward. Let's say you went with a spring about 5x weaker, you could run the gun between 120-200psi. The way I would do this would be to remove all of the internals of the valve except for the on/off assembly. Replace the back reg with a hollow air chamber to store more available air. On the retro valve, you would have to plug the little hole on the side that goes into the piston assembly, so air doesn't leak out. Some of the air passageways would maybe need to be enlarged. A good lp reg with great flow capabiltity's would also be needed. Now your velocity is controled by your input pressure. 120psi may give you 200 fps. 190psi may give you 280's.
I cool test to do is to remove the brass reg seat thingy that is held in place by the back reg. Next have an accurate way to measure input pressure. Start out around 300 psi and chrono the gun. Now put 350 or 400psi into the gun and re-chrono. See what kind of input pressure it takes to get to a desired velocity and that pressure will be the working pressure of your valve(at a specific velocity of course). If you try to rapid fire without this piece you will have major shootdown.
Sure if you go with a lighter bolt spring your bolt won't return as fast, but if it came down to getting a couple hundred extra shots per tank and less barrel breaks(assuming this would slow down bolt speed making it easier on the next ball in the stack), vs being able to shoot 18sps, I know what I would favor, do you?
This would be interesting to test out. I may have to go remove my bolt spring and the brass reg seat thing, put 120psi into the gun and see what it chrono's in at. If anyone else tries this, let us know back here.
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