Catweazle Posted January 27, 2012 Report Share Posted January 27, 2012 Assuming the muzzle is on the centre line of the moderator, the blast will be hitting the outer walls and reflecting back to the centre where it will once again become a high pressure area, just what we're trying to avoid. Would it be better if we used, for example, a square section body that would reflect the blast back spread over a longer period ? Quote Link to comment Share on other sites More sharing options...
hambone Posted January 27, 2012 Report Share Posted January 27, 2012 Assuming the muzzle is on the centre line of the moderator, the blast will be hitting the outer walls and reflecting back to the centre where it will once again become a high pressure area, just what we're trying to avoid. Would it be better if we used, for example, a square section body that would reflect the blast back spread over a longer period ? Dunno :unsure: Quote Link to comment Share on other sites More sharing options...
yankeedoodlepigeon Posted January 27, 2012 Report Share Posted January 27, 2012 Yes but there should be a baffle just before it meets the centre again and so on. Quote Link to comment Share on other sites More sharing options...
Catweazle Posted January 27, 2012 Author Report Share Posted January 27, 2012 Yes but there should be a baffle just before it meets the centre again and so on. Many moderators are symmetrical, so it looks to me as if there will still be a point in the centre line where the high pressure is re-created by the reflected blast. Quote Link to comment Share on other sites More sharing options...
Coolhead Posted January 27, 2012 Report Share Posted January 27, 2012 Pressure doesn't bounce like a ball. A mod is a sealed space where fast-moving high pressure gas can expand and slow. The jet of gas from a muzzle blast causes turbulence where it meets the external atmosphere. By expanding the gas and putting obstacles in its path to slow it, the turbulence is reduced. Any improvements made by changing the shape would be outweighed by it's reduced practicality. A blanked-off and baffled trumpet flare would be best but totally unusable. Quote Link to comment Share on other sites More sharing options...
Catweazle Posted January 27, 2012 Author Report Share Posted January 27, 2012 Pressure doesn't bounce like a ball. A mod is a sealed space where fast-moving high pressure gas can expand and slow. The jet of gas from a muzzle blast causes turbulence where it meets the external atmosphere. By expanding the gas and putting obstacles in its path to slow it, the turbulence is reduced. Any improvements made by changing the shape would be outweighed by it's reduced practicality. A blanked-off and baffled trumpet flare would be best but totally unusable. My point is that with a cylindrical, baffled, moderator, the blast expands from the centre and bounces back from the outside into a point of high pressure right back in the middle where the hole to the next section of the moderator is. Perhaps a practical test is called for, I have some stainless box-section. The baffles won't be as easy to make though, maybe that's the real reason mods are round. Quote Link to comment Share on other sites More sharing options...
bedwards1966 Posted January 27, 2012 Report Share Posted January 27, 2012 I expect that you may be right regarding the sound bouncing back, it's quite possible that they are made round as it's easier and looks and handles better. Lets face it, how many people would buy a mod made of box section or other non rounded shape? It would be interesting to experiment a little though, see if your right Quote Link to comment Share on other sites More sharing options...
Dekers Posted January 27, 2012 Report Share Posted January 27, 2012 My point is that with a cylindrical, baffled, moderator, the blast expands from the centre and bounces back from the outside into a point of high pressure right back in the middle where the hole to the next section of the moderator is. Perhaps a practical test is called for, I have some stainless box-section. The baffles won't be as easy to make though, maybe that's the real reason mods are round. There is very little that we cannot improve, but a balance has to be drawn between levels of improvement, practicality and cost. Very high pressure can also occur in some calibres, cylinders do not suffer the same stress points as squares! All my centrefires are VERY accurate with the right ammo and the mod, even though all my CF's are field tools and not target rifles, I have achieved all but one hole groups with my .243, so any pressure anomalies in a round mod don't seem to be having that much effect. Quote Link to comment Share on other sites More sharing options...
lambhat Posted January 27, 2012 Report Share Posted January 27, 2012 I'm guessing that a mod works by spreading the pressure wave from the muzzle over time, so the wave exits the hole in the end of the mod less sharply. If that's correct then I don't think it matters much if reflections off the first baffle make a pressure spike on the centre axis of the mod. That pressure spike would eventually exit the hole at a different time from the other reflections, so the mod would have done its job. Quote Link to comment Share on other sites More sharing options...
Coolhead Posted January 28, 2012 Report Share Posted January 28, 2012 People are confusing pressure with sound. Pressure just does not bounce. The jet exiting the muzzle will gradually diffuse throughout the enclosed space. When it exits it is going slowly enough to mix much more easily with the atmosphere. It is not possible to "focus" pressure. The shape of the space is irrelevant but a cylinder is practical and cheap to manufacture. Quote Link to comment Share on other sites More sharing options...
yankeedoodlepigeon Posted January 28, 2012 Report Share Posted January 28, 2012 I thought pressure did bounce and that's how a 2 stroke motorcycle exhaust works Quote Link to comment Share on other sites More sharing options...
yankeedoodlepigeon Posted January 28, 2012 Report Share Posted January 28, 2012 http://www.motorcycle.com/how-to/how-twostroke-expansion-chambers-work-and-why-you-should-care-3423.html Quote Link to comment Share on other sites More sharing options...
Catweazle Posted January 28, 2012 Author Report Share Posted January 28, 2012 People are confusing pressure with sound. Pressure just does not bounce. Sound is pressure. It's a pressure wave travelling through the air. Sound does bounce. Quote Link to comment Share on other sites More sharing options...
Coolhead Posted January 28, 2012 Report Share Posted January 28, 2012 A tuned exhaust on any engine creates standing shock waves. These resonance waves, being sound, are comprised of a local wavefront of kinetically energised pressure pulses. Static pressure, which is the basic pressure in a system, is unaffected by localised sound waves or the effect of rapidly moving gasses bearing down less hard then still ones (Dynamic pressure.) The sea surface doesn't vary in pressure because it has high energy waves in it. kinetically energised wave pulses can indeed be reflected from surfaces but the base medium fluids will always find their own level in a closed system. Moderators work on the principles of Boyle's Law and Drag. Quote Link to comment Share on other sites More sharing options...
Catweazle Posted January 28, 2012 Author Report Share Posted January 28, 2012 I appreciate the role of cooling and expansion in moderator design, but I'm wondering if mechanical means of disrupting the intense peak pressure could be made more efficient than they are now. I think an experiment is in order. Quote Link to comment Share on other sites More sharing options...
Coolhead Posted January 28, 2012 Report Share Posted January 28, 2012 I appreciate the role of cooling and expansion in moderator design, but I'm wondering if mechanical means of disrupting the intense peak pressure could be made more efficient than they are now. I think an experiment is in order. My last project before I left engineering was a new mod design. If I still had access to machine tools I'd like to try more designs. It worked as well as commercial ones on an air gun but if I put it on my rifles I'd have to register it. The police said it's fine to add your own kit to your ticket but please proof it and show us that you are competent. I so can't be bothered with that. Quote Link to comment Share on other sites More sharing options...
Catweazle Posted January 28, 2012 Author Report Share Posted January 28, 2012 I'd be interested in any ideas you would care to share. Quote Link to comment Share on other sites More sharing options...
Coolhead Posted January 29, 2012 Report Share Posted January 29, 2012 (edited) This is what I made. This was first one I'd made but the second design of core. The two holes in the back end serve the purposes of being a peg spanner attachment, a bit of a muzzle brake and a safety valve to limit the peak pressure as I was being extra cautious. The adapter at the end is to suit a 15mm Air Arms S200. It's never been on a firearm but I'm convinced it is more than strong enough. Edited January 29, 2012 by Coolhead Quote Link to comment Share on other sites More sharing options...
peck Posted February 5, 2012 Report Share Posted February 5, 2012 (edited) i think the reason that mods are cylindrical is that no matter how far they are screwed onto the barrel the pressure is equal on all sides. and as for "It is not possible to "focus" pressure" , not true, ask Mr Charles E. Munroe. Edited February 5, 2012 by peck Quote Link to comment Share on other sites More sharing options...
Paul61 Posted February 5, 2012 Report Share Posted February 5, 2012 Has anyone made a moderator from Polyurathane? light, elastic properties for expansion, cheap to produce from simple tooling, would allow the use of some interesting baffles and chambers for expansion. Probably dishwasher safe for cleaning Quote Link to comment Share on other sites More sharing options...
Catweazle Posted February 5, 2012 Author Report Share Posted February 5, 2012 Nice looking work Coolhead, thanks for posting Quote Link to comment Share on other sites More sharing options...
Coolhead Posted February 5, 2012 Report Share Posted February 5, 2012 Has anyone made a moderator from Polyurathane? light, elastic properties for expansion, cheap to produce from simple tooling, would allow the use of some interesting baffles and chambers for expansion. Probably dishwasher safe for cleaning Yes it is done with air guns but plastics can't cope with extended exposure to burning powder. Quote Link to comment Share on other sites More sharing options...
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