hi folks, sorry sticking my nose......and sorry for my english as well...
I Have some mirages in my canteen and I tried some way to improve power as did not want to load the gun more than 32 atm....
I tell you what I did..
1) I found out that the oil inside the gun is a great obstacle to the air flux through small holes and narrow tunnels....
try this test: just pump 4/5 strokes with the lower barrel then, without loading the shaft, flip the knob to maximum speed... at that point you will hear some noises going on for seconds and if you do the same test without oil inside the gun you will notice that the air transfer will be immediate without any kind of noises...of course, to do that you need to dismantle the gun often, grease the barrels and using a piston with a small tank full of oil between the two oring and to be an happy spare compressor owner...
2) I drilled an hole (about 8/9mm) on the upper side of the barrel just like the other guns and then I milled a recess as deep as 1 mm as large as the hole starting from the hole towards the head....the recess should pass the handle for about one inches without getting close to the bulkhead....the recess in the top of the barrel should be made by using a small mill that goes back and forth in order to keep a deepness of 1mm constant from side ti side....
3) In the past I used to build the lower barrel 9/13mm and the upper barrel with 14mm bore in order to keep high power with low pressure...
The oil should not influence the power of the gun as it pushes through the holes very quickly, like paint from a spray gun, only the SAE 10 viscosity oil is much thinner than any paint. When you do the test with the rear of the gun depressurized after conducting five strokes of the pumping barrel and the selector knob being flipped up the inner barrel, pre-chamber (interior spaces of the handle and the well inside the partitioning bulkhead, if there is one) and the pumping barrel have very little air pressure inside them until the transfer port unplugs. This is the situation with the spear yet to be inserted in the main barrel. The high pressure air has all been stored in the front tank, but with the transfer port open it rushes through into the pre-chamber where some of it moves through the rectangular channel in the handle to fill the inner barrel and some of it moves through the small hole at the front of the rectangular channel to access the inlet valve of the pumping barrel to refill that barrel. The gurgling noises that you can hear is the pumping barrel pressure equalizing with the pressure in the front tank as the pressure throughout the entire gun equalizes, the pumping barrel having a ball type inlet valve and an expanding rubber tube outlet valve. Air is moving internally with high velocity initially, but that falls off as the pressure differentials inside the gun disappear.
When the gun actually shoots you can never hear it, but the same equalizing action goes on in the pumping barrel. As "cocked to shoot" pressure departs the front tank the same pressure inside the pumping barrel can only participate in the shot by opening the rubber tube valve as it cannot flow back through the pumping barrel's inlet valve, so as the gun equalizes its internal volumes back to initial charge pressure the pumping barrel valves are working because the pumping barrel is isolated by its two valves from the other spaces inside the gun which are all interconnected with the transfer port open. In a sense the interior of the pumping barrel lags behind the shot, but only when the pressure imbalances are getting smaller and the valves are resisting opening due to their "springs". Of course with no oil in the gun you will not hear anything, but don't confuse these gurgling noises with airflow restriction except at low pressure differentials when the shaft will have already left the gun. The rubber tube valve operates every time the "Mirage" shoots except when taking a shot with the selector knob in position #1 as then the front tank and pumping barrel are both isolated.
Very interesting to hear of your longer gun conversions which means you have access to the tubing needed. Many years ago I looked for such alloy tubing here, but nothing was available in the diameters required, or the grade of alloy and I gave up on the idea of building a different type of pneumatic gun (not a "Mirage"!).
The improvements to breathing in the "Mirage" were probably also known to Mares, but they had to create shapes that could be extracted from the moulding die and that eliminates any undercuts inside the handle to add recessed grooves. Wall thickness needs to be considered as at 40 bar they could not risk the plastic components bursting, so bar the blind ended holes the "Mirage" handle moulding is rather solid in construction. The rear end of the early inner barrel is somewhat different to that in the later guns as Mares tried improving the breathing there with a larger rectangular opening, but the limitation was really the cross-section of the rectangular channel as its floor is elevated by the presence of the support structure for the pumping barrel inlet valve seat. As for economic reasons guns have to be churned out quickly there was no time for hand working of components, thus the only post-moulding work on the handle is the small connecting hole in the floor of the rectangular channel creating an air pathway to the pumping barrel inlet valve. It ingeniously makes use of what is one of the blind ended holes created by the withdrawing moulding die inserts, they just had to put a plug with a hole in it to create the valve seat at the front of that blind hole.
What the revised "Mirage" needed was a completely new rear handle, but the easiest thing to change was the partitioning bulkhead and then they could still use most of the existing components, although the inner barrel is different as the "O" ring grooves are in different positions. It is possible Mares could make a completely new "Mirage" based on the "Cyrano Evo" handle and main barrel, but they would need a different partitioning bulkhead and of course the inner barrel would need to be of a larger diameter. However given the emergence of vacuum barrels and the increasing reluctance to create very high pressure guns a new "Mirage" is less likely as there needs to be enough demand to justify the production in terms of the cost in producing the gun and what price the gun would sell for. The "Mirage" when first released here was twice the price of anything else from Mares in terms of their rear handle pneumatic guns and was seen as being too short, but the "Mirage" was then offered as a compact, yet powerful gun (refer to the original documentation). Unfortunately it was not as my "Sten" at high pressure, but under 40 bar, could outshoot it, but I put that down to the "Sten" being a longer gun. That is why largely unused "Mirage" guns went into storage, joining the leaking examples that owners had given up on.
