The Background
In preparation for a new bluewater build, I have been thinking about muzzle seals. The Vuoto/UBL seals don't fare well with 8.5-9mm shafts and I want to be able to shoot those. One way around that is to try to make my own conical vacuum cuffs from casting PU into 3D printed molds. I might still try that.
But I also started thinking about an old Evo Air muzzle that I have. That design got a bit of a bad rep in Italy but I actually really like it. Its whole claim to fame was that the o-ring would move into a larger cavity during the shot and thus greatly reduce friction. But I think it was proven that the o-ring does not actually move forward during the shot as intended - the vacuum holds it in place in the tighter o-ring groove. Personally, I think the real benefit was that it could be loaded submerged and while that feature might have been unintended, it is one that I refuse to live without.
Now, Seatec only designed the Evo Air muzzle to work with 7mm front-tied shafts, but I am thinking that the movable o-ring design might actually work for shafts with a tail end, too... Especially since Dima's tail ends are only 1mm larger in diameter than the shaft itself. So, with some careful o-ring design, keeping gaps to the bare minimum, proper testing and a bit of luck, it might actually work.
I am still not back to my machines in China, so it will take a while to try this out.
But let's start this off with some fancy renderings. All of them are missing a slide ring, but just imagine it is sitting in the bore in the red front part of the muzzle.
I started off with a design in two parts - it could be an alu rear and Delrin front:
The little blind hole at the top is for a DIY wrench - Dima does it this way and it's easier to fabricate for me than milling flats and also, the tool can be made really lightweight, so you don't have to travel with a real spanner.
But given that the the gaps between the inner walls and the shaft has to be kept to an absolute minimum for the o-ring not to migrate to the vacuum side I realized the two part design would likely only work with one given shaft thickness, so I drew up a more modular, three part muzzle:
The rear part and the shock absorber could be titanium. It is not that easy for me to machine titanium but in this version, we are talking fairly simple parts, so it might be doable. The middle and front parts wont take much impact so Delrin should suffice. It is light, easy to machine and really slippery which should work well for the o-ring seat. Also, the middle and front parts could be changed out for when using different sizes of shafts - importantly, without having to depressurize the gun.
Now, let's look at the guts:
Finally, two screen grabs; one showing the muzzle in the loading position:
The red front part will be unscrewed two full turns, moving it 5mm forwards at the end of the loading process. This way, the o-ring can move forward into the bigger groove and hopefully, let the tail end through without too much friction or damaging the o-ring, So, at the end of the shot, it would look like this:
Now, this is just an idea and it might not work, but I am willing to try it out. Of course, the o-rings will be punished a bit but even if they only last a few days, it wouldn't be an issue changing them out on a trip or even in the boat. In the drawings above, the o-ring has a cross section of 3mm and I would think going as big as I can on the cross section would help reduce the risk of the o-ring getting sucked into the gap. On the other hand, thicker rings don't stretch as easily.
Once, I get back to China it should be fairly easy to test this concept out with some Delrin and/or 3D printed prototypes.
BTW; The three part muzzle, if made in titanium and Delrin according to this design would weigh around 55g and be 75mm long. That's 22g lighter than the Evo Air and 18mm shorter. It is also only 7g heavier and 7mm longer than a Vuoto muzzle.
In preparation for a new bluewater build, I have been thinking about muzzle seals. The Vuoto/UBL seals don't fare well with 8.5-9mm shafts and I want to be able to shoot those. One way around that is to try to make my own conical vacuum cuffs from casting PU into 3D printed molds. I might still try that.
But I also started thinking about an old Evo Air muzzle that I have. That design got a bit of a bad rep in Italy but I actually really like it. Its whole claim to fame was that the o-ring would move into a larger cavity during the shot and thus greatly reduce friction. But I think it was proven that the o-ring does not actually move forward during the shot as intended - the vacuum holds it in place in the tighter o-ring groove. Personally, I think the real benefit was that it could be loaded submerged and while that feature might have been unintended, it is one that I refuse to live without.
Now, Seatec only designed the Evo Air muzzle to work with 7mm front-tied shafts, but I am thinking that the movable o-ring design might actually work for shafts with a tail end, too... Especially since Dima's tail ends are only 1mm larger in diameter than the shaft itself. So, with some careful o-ring design, keeping gaps to the bare minimum, proper testing and a bit of luck, it might actually work.
I am still not back to my machines in China, so it will take a while to try this out.
But let's start this off with some fancy renderings. All of them are missing a slide ring, but just imagine it is sitting in the bore in the red front part of the muzzle.
I started off with a design in two parts - it could be an alu rear and Delrin front:
The little blind hole at the top is for a DIY wrench - Dima does it this way and it's easier to fabricate for me than milling flats and also, the tool can be made really lightweight, so you don't have to travel with a real spanner.
But given that the the gaps between the inner walls and the shaft has to be kept to an absolute minimum for the o-ring not to migrate to the vacuum side I realized the two part design would likely only work with one given shaft thickness, so I drew up a more modular, three part muzzle:
The rear part and the shock absorber could be titanium. It is not that easy for me to machine titanium but in this version, we are talking fairly simple parts, so it might be doable. The middle and front parts wont take much impact so Delrin should suffice. It is light, easy to machine and really slippery which should work well for the o-ring seat. Also, the middle and front parts could be changed out for when using different sizes of shafts - importantly, without having to depressurize the gun.
Now, let's look at the guts:
Finally, two screen grabs; one showing the muzzle in the loading position:
The red front part will be unscrewed two full turns, moving it 5mm forwards at the end of the loading process. This way, the o-ring can move forward into the bigger groove and hopefully, let the tail end through without too much friction or damaging the o-ring, So, at the end of the shot, it would look like this:
Now, this is just an idea and it might not work, but I am willing to try it out. Of course, the o-rings will be punished a bit but even if they only last a few days, it wouldn't be an issue changing them out on a trip or even in the boat. In the drawings above, the o-ring has a cross section of 3mm and I would think going as big as I can on the cross section would help reduce the risk of the o-ring getting sucked into the gap. On the other hand, thicker rings don't stretch as easily.
Once, I get back to China it should be fairly easy to test this concept out with some Delrin and/or 3D printed prototypes.
BTW; The three part muzzle, if made in titanium and Delrin according to this design would weigh around 55g and be 75mm long. That's 22g lighter than the Evo Air and 18mm shorter. It is also only 7g heavier and 7mm longer than a Vuoto muzzle.
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