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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Does A Can or Suppresor Increase Back Pressure and Decrease Velocity??? Well????
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<blockquote data-quote="bengineer" data-source="post: 2439343" data-attributes="member: 36951"><p>I haven't read all the responses on pages 2-4, but I am tired from reading the original post. Tired because there are several false assumptions and misunderstandings that I fear people walk away from this with gravely mistaken notions. I do not mean to condescend, but merely to inform. I don't correct people's grammar or spelling on this forum because it is condescending.</p><p></p><p>Pressure is measured in force per (unit) area. We always break this down to single unit area, rather than leave it as a weird fraction. Gauges display in unit area, whether you prefer psi or Pascals.</p><p></p><p>Pressure absolute (psia) is what we are under anywhere we are, based on what we are in. At the bottom of a swimming pool, we have the mass of the water and the air in the atmosphere pushing down on us. At the side of the same pool, we have just the air (unless the HVAC system isn't balanced). On the moon, we are at 0psia. The inside of your bore and the inside of your can attached to said bore are at the same pressure, whether you're atop Everest or in Death Valley. Please, let's not think of that assembly at the bottom of the swimming pool.</p><p></p><p>Pressure gauge (psig) is what is measured on a gauge, inside a pressure vessel, such as a basketball, or your barrel/silencer. A gauge that is not attached to anything, just in your hand, will read 0 if it is calibrated correctly. The gauge pressure may also read negative, indicating the gauge pressure is lower than the ambient pressure (inside a conventional light bulb, for example - though I have never seen a pressure gauge on a light bulb).</p><p></p><p>Backpressure. This is a word often thrown around, but is quite misleading. Pressure is pressure. Increased resistance can increase pressure in a system, such as your gun barrel (longer-than-expected bearing surface, rust, mud, etc). Decreased resistance, such as HBN or Moly on bullets, or cast bullets, can decrease pressure in a system. Adding a can/silencer to a barrel doesn't increase resistance, but it does increase dwell time of the bullet and expanding/expanded gases, which slows the decrease in pressure as compared to no can/silencer. This gives the illusion of "backpressure," but the can really doesn't create anything; the can just holds pressure longer. That provides the perceived recoil mitigation of the can (mostly). But it does not cause "backpressure."</p><p></p><p>Same goes for cans on a gas gun. More combustion gases come out of the gas port and into my right eye because pressure is held longer in the can. Also, the slower decline of pressure due to the can may also push more gas into the gas system, possibly sending even more gases into my shooting eye.</p><p></p><p>I have fiddled a little with coefficients of friction or surface polish of both reloading dies and chambers. Just a little, though. I haven't seen anything conclusive to lead me to see that brass needs roughness or chambers need some level of roughness/texture (as opposed to absolute mirror finish) in order for things to work correctly, or prevent case head separation, or primers from backing out. I have heard all manner of stories and opinions, from 'brass has to grip the rough chamber or it will cause brass flow out of the action' to 'chambers have to be smooth or the brass will grip and cause primers to back out without the case head pushed against the bolt face.' None of these kinds of statements are based in quantitative fact, but are of opinion. Much like some other areas of interest, say, on the TV at 6:00. Opinions are important to their respective owners, but they are not valuable in discussions like this thread. And don't forget that an anecdote isn't enough sample to have a valid conclusion.</p></blockquote><p></p>
[QUOTE="bengineer, post: 2439343, member: 36951"] I haven't read all the responses on pages 2-4, but I am tired from reading the original post. Tired because there are several false assumptions and misunderstandings that I fear people walk away from this with gravely mistaken notions. I do not mean to condescend, but merely to inform. I don't correct people's grammar or spelling on this forum because it is condescending. Pressure is measured in force per (unit) area. We always break this down to single unit area, rather than leave it as a weird fraction. Gauges display in unit area, whether you prefer psi or Pascals. Pressure absolute (psia) is what we are under anywhere we are, based on what we are in. At the bottom of a swimming pool, we have the mass of the water and the air in the atmosphere pushing down on us. At the side of the same pool, we have just the air (unless the HVAC system isn't balanced). On the moon, we are at 0psia. The inside of your bore and the inside of your can attached to said bore are at the same pressure, whether you're atop Everest or in Death Valley. Please, let's not think of that assembly at the bottom of the swimming pool. Pressure gauge (psig) is what is measured on a gauge, inside a pressure vessel, such as a basketball, or your barrel/silencer. A gauge that is not attached to anything, just in your hand, will read 0 if it is calibrated correctly. The gauge pressure may also read negative, indicating the gauge pressure is lower than the ambient pressure (inside a conventional light bulb, for example - though I have never seen a pressure gauge on a light bulb). Backpressure. This is a word often thrown around, but is quite misleading. Pressure is pressure. Increased resistance can increase pressure in a system, such as your gun barrel (longer-than-expected bearing surface, rust, mud, etc). Decreased resistance, such as HBN or Moly on bullets, or cast bullets, can decrease pressure in a system. Adding a can/silencer to a barrel doesn't increase resistance, but it does increase dwell time of the bullet and expanding/expanded gases, which slows the decrease in pressure as compared to no can/silencer. This gives the illusion of "backpressure," but the can really doesn't create anything; the can just holds pressure longer. That provides the perceived recoil mitigation of the can (mostly). But it does not cause "backpressure." Same goes for cans on a gas gun. More combustion gases come out of the gas port and into my right eye because pressure is held longer in the can. Also, the slower decline of pressure due to the can may also push more gas into the gas system, possibly sending even more gases into my shooting eye. I have fiddled a little with coefficients of friction or surface polish of both reloading dies and chambers. Just a little, though. I haven't seen anything conclusive to lead me to see that brass needs roughness or chambers need some level of roughness/texture (as opposed to absolute mirror finish) in order for things to work correctly, or prevent case head separation, or primers from backing out. I have heard all manner of stories and opinions, from 'brass has to grip the rough chamber or it will cause brass flow out of the action' to 'chambers have to be smooth or the brass will grip and cause primers to back out without the case head pushed against the bolt face.' None of these kinds of statements are based in quantitative fact, but are of opinion. Much like some other areas of interest, say, on the TV at 6:00. Opinions are important to their respective owners, but they are not valuable in discussions like this thread. And don't forget that an anecdote isn't enough sample to have a valid conclusion. [/QUOTE]
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Does A Can or Suppresor Increase Back Pressure and Decrease Velocity??? Well????
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