Carl, there is a significant part of the recoil due to accelerating the air mass out the muzzle.... Helium is 1/7th the density of air, so there will be only 1/7th the mass being accelerated.... That additional available energy can be used to accelerate the bullet, that is EXACTLY where the extra velocity comes from when you use Helium.... Yes, the bullet will end up going faster, and there will be more recoil from that.... but there will be only 1/7th the recoil from accelerating Helium instead of air.... It should, relatively speaking, be a wash....Assuming my numbers for the gun are correct.... Reservoir = 800 ccBarrel volume = 2^2 x PI/4 x 110 = 345 ccStarting pressure = 265 barMuzzle pressure = 265 x 800 / (800+345) = 185 barAir density at 185 bar = 216 kg/m^3 = 0.216 g/ccMass of air in the barrel = 345 x 0.216 = 74.5 grams = 1150 grainsFor Helium, density at 185 bar = 28 kg/m^3 = 0.028 g/ccMass of Helium in the barrel = 345 x 0.028 = 9.66 grams = 149 grainsTherefore, using Helium instead of air, there is over 1000 grains less mass being accelerated out the barrel.... assuming an 80 bar pressure drop during the shot.... If the pressure drop in the reservoir is less, then all numbers are reduced by the same ratios.... If, on the other hand, the valve dumps and empties the reservoir, the entire air mass of 234 grams (3617 grains) would be exhausted through the muzzle, causing more recoil than the bullet itself.... Bob
I think Newtons Third Law of Motion will apply "Newton's Third Law of Motion. It states, “For every action, there is an equal and opposite reaction.” Forces always occur in pairs; when one body pushes against another, the second body pushes back just as hard."Going further as you guys are talking--"According to the law, the force exerted by object 1 upon object 2 is equal in magnitude and opposite in direction to the force exerted by object 2 upon object 1."Not being a PHD in Physics, I would think accelerating that 2500 gr bullet FASTER by whatever means will also get MORE RECOIL. This will be true as in my years of powder reloading, lighter accelerated loads=mild recoil and the faster even a light bullet is accelerated, the MORE FELT RECOIL, ALWAYS. No matter what size bullet you are accelerating. Can't change the laws of Physics.In ENGINEERING there are no free lunches.....Get something here, usually give up something elsewhere. In the helium discussion, probably get more fps and fpe but will get correspondingly MORE RECOIL. Helium won't double the power on that big bore but will be easily 50% more of EVERYTHING. MARKO, you will FEEL THE LOVE when you touch that puppy off Carl
.. The recoil and noise were also dramatically reduced.... Note I mentioned above that if the gun dumped all the air, there would be more recoil from the air than from the bullet....Bob
All good and fun, guys. Video from the track, one of our fellow shooters trying the 20mm out. He did not see anybody else shoot it before and was not fully prepared for the recoil. Marko
With my previous experience shooting bigbores on helium, the recoil will be worse. The gas speed is so much faster, it will dump way more helium than air. I have one week till next track session to make some modifications to the rifle and manufacture a brake for it. Then we will know how it will do on helium. The gun can take extra punishment that helium puts on it. Lets find out where the limit is for now, someone will no doubt push further one day. Marko
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