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Air Gun Home Forum Index » General Air Gun Questions and Topics » Sound Barrier Goto page 1, 2  Next    View previous topic :: View next topic  Sound Barrier   Posted: Fri Jan 28, 2011 11:47 am oddtodd Silver Status Member Joined: 30 Dec 2008 Posts: 2029 Location: Richmond, IN USA How fast does a pellet need to go before hitting the sound better?It's a benjamin RS2. I hear a very distinct crack when I shoot it. I already cleaned the barrel spotless and I can't see any oil in the transfer port. I know it's a lot harder to cock than my storm XT. It's supposed to be a 1000 fps rifle, but we all know how manufacturers like to inflate numbers. I am just curious if I am, because that way I need to go to a heavier pellet. I'd like to know I am hitting harder too. _________________ Airguns: Two starlings talking "Larry, did you hear that? Larry?? LARRY!!!!"   Posted: Fri Jan 28, 2011 1:24 pm walter Veteran Member Joined: 12 Nov 2010 Posts: 181 Location: towson md. i though it was around 1100 give or take. _________________ modified 1377c. first gen. Beeman hw97k. 177.cal.   Posted: Fri Jan 28, 2011 1:32 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC It depends on the temperature and to a slight extent on the humidity and air pressure.... It does NOT depend of the altitude as many believe.... http://www.sengpielaudio.com/calculator-airpressure.htm The short answer is ~1128 fps at 20*C (68*F).... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Fri Jan 28, 2011 7:03 pm donec Senior Member Joined: 19 Dec 2009 Posts: 836 Location: central Texas Pflugerville area That crack could just be the echo of the dieseling. It may not mean your are breaking the sound barrier,   Posted: Sat Jan 29, 2011 8:02 am jlwilliams Veteran Member Joined: 02 Oct 2009 Posts: 264 Location: Jacksonville, NC USA Try a heavier pellet. If there is still a crack, it's probably dieseling. If the heavier pellet doesn't crack thean it probably is pushing the light ones over 1100 Sound Barrier   Posted: Thu Feb 17, 2011 11:04 am ericb New Member Joined: 16 Feb 2011 Posts: 6 Location: Glasgow I've built a QB 78 and using an extended tube, pumped it to 2000PSI and it shoots a 5 grain Thunderbolt pellet at 1426 FPS and very accurate. This easily breaks the sound barrier ( 1116 fps at sea level ) it gives an amazing crack when doing so. If I fire indoors at 30 yards......nothing. It only seems to do it in the field and when it's out a bit, giving me the impression the pellet is still accelerating. Eric   Posted: Thu Feb 17, 2011 12:38 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC Quote: giving me the impression the pellet is still accelerating. Sorry, absolutely impossible, there is no force available to accelerate the pellet after it leaves the muzzle, only slow it down.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count! Sound barrier   Posted: Thu Feb 17, 2011 1:16 pm ericb New Member Joined: 16 Feb 2011 Posts: 6 Location: Glasgow I do bow to your greater knowledge, but why the difference do you think. I shot indoors at 85 ft and only the report of the initial firing, but in the field definately a second crack. Eric   Posted: Thu Feb 17, 2011 2:41 pm broommaster2000 Moderator Joined: 10 Mar 2007 Posts: 5714 Location: City of Groningen, Groningen, The Netherlands Impact? _________________ BIG GAP   Posted: Thu Feb 17, 2011 3:08 pm rsterne Moderator Joined: 15 Jan 2008 Posts: 2998 Location: Coalmont, BC An Echo?.... Bob _________________ Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! Airsonal: Too many to count!   Posted: Thu Feb 17, 2011 9:50 pm jlwilliams Veteran Member Joined: 02 Oct 2009 Posts: 264 Location: Jacksonville, NC USA Sonic crack is somehow related to how much distance you have. Long story short, a supersonic projo fired into a bucket of sand a couple feet away doesn't go crack. Same projo same gun same weather fired at a target across the field does. I don't know why but I have observed it before more than once.   Posted: Thu Feb 17, 2011 10:02 pm sniper Silver Status Member Joined: 28 Nov 2008 Posts: 3752 Location: Star, Idaho Todd, you didn't list pellet weight. I once (stupidly) shot some crosman silver eagles-4.8 grain thru my .177 gamo hunter 440 and hit 1030 fps. (I have a chrony) there was a definite crack compared to 7.9's @840. Still 100 fps below the sound barrier. I assumed it was piston slam. Maybe unsused air at the muzzle??? _________________ I believe in gun control, If there's a gun around I want to be controlling it.......   Posted: Fri Feb 18, 2011 1:15 am kanyon Silver Status Member Joined: 09 Aug 2008 Posts: 1582 Location: New Zealand rsterne wrote: It depends on the temperature and to a slight extent on the humidity and air pressure.... It does NOT depend of the altitude as many believe.... http://www.sengpielaudio.com/calculator-airpressure.htm The short answer is ~1128 fps at 20*C (68*F).... Bob dosn't air pressure & altitude go hand in hand Or is not enough to have a efect _________________ Career Infinity PCP .22 Webley Patriot .25 Hatsan mod 75 .22 Hatsan mod 99 .177 (Quattro & SAS) Kral underlever .177 ............................................. . sound barrier   Posted: Fri Feb 18, 2011 4:11 am ericb New Member Joined: 16 Feb 2011 Posts: 6 Location: Glasgow I shot in the air, so no impact noise. I also let a few people hear it, and they all asked what the noise was. My mate shot at a target at 50 yards and even the 5 grain pellet made an audible whack when it hit. And yes it was very accurate. I have two rifles that do it.......this one does it with 7.9 grain pellets as well. I'm hopeing for a misty day to try and fire into it, to see if anything is visible ? Anyone tried this ? Eric   Posted: Fri Feb 18, 2011 10:27 am Slavia Moderator Joined: 31 Mar 2008 Posts: 4382 Location: Waseca, Minnesota, USA Quote: dosn't air pressure & altitude go hand in hand Rsterne is correct - temperature is the biggest factor. It's true that the speed of sound is lower at higher altitudes, but that's because the temperature is less. If you go really high (like 60,000'+, or into the ozone layer) the temperature increases, even though there isn't much pressure. The speed of sound actually increases at those altitudes, because of the temperature. http://en.wikipedia.org/wiki/Speed_of_sound _________________ ¡Listo! ¡Apunte! ¡Fuego! 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