Will_M Posted September 5, 2009 Share Posted September 5, 2009 I started a thread in the .40 loading section but I thought this topic fit better here. I just loaded up some rounds to try to make major out of my M&P40. 170 grain precision molys, loaded to 1.130", I also had to use 5.5 grains of WST (we'll get to that in a minute). I stopped every 5 rounds while loading on my 550 to check the powder charge, and got the usual tiny bit of variance (i'm using a balance scale) but at the chrono, my velocities were all over the place. #1: 920 #2: 1012 #3: 956 #4: 905 #5: 1001 #6: 1032 I'm using a shooting chrony F1. Could the crappy chrono be the problem? Should I switch to chrono with my Pact MKIV? Link to comment Share on other sites More sharing options...
Jman Posted September 5, 2009 Share Posted September 5, 2009 Will, those are fairly extreme velocities spreads. Pay particular attention to the distance from the muzzle to the first sensor. Before switching chronos make sure that your not picking up some muzzle blast. That could very well be the problem. I used my F1 with good results in the shade about 12-14 feet from the muzzle. If your results stay the same, report back. Jim Link to comment Share on other sites More sharing options...
Will_M Posted September 5, 2009 Author Share Posted September 5, 2009 Will, those are fairly extreme velocities spreads. Pay particular attention to the distance from the muzzle to the first sensor. Before switching chronos make sure that your not picking up some muzzle blast. That could very well be the problem. I used my F1 with good results in the shade about 12-14 feet from the muzzle. If your results stay the same, report back.Jim Thanks for the quick response, Jim. I'm going back out early in the morning and try it in the shade. What do you mean it could be picking up muzzle blast? Link to comment Share on other sites More sharing options...
atbarr Posted September 5, 2009 Share Posted September 5, 2009 I had a similar problem, it was very cloudy and a light rain. I went back the next day and the results were much better. As far as muzzle blast, that means you might have been too close to the chrono. A.T. Link to comment Share on other sites More sharing options...
Will_M Posted September 5, 2009 Author Share Posted September 5, 2009 I had a similar problem, it was very cloudy and a light rain. I went back the next day and the results were much better. As far as muzzle blast, that means you might have been too close to the chrono.A.T. The skies were clear. Maybe I should back up further? Around 20 feet or so just to see if I'll get consistent readings? Link to comment Share on other sites More sharing options...
mscott Posted September 5, 2009 Share Posted September 5, 2009 (edited) If shooting in the shade doesn't prove to be better, check for bullet set back. Either try to push the bullet into the case by pushing against a bench or chamber it a couple of times and then measure OAL. 5.7 of WST should be PLENTY for major. Edited September 5, 2009 by mscott Link to comment Share on other sites More sharing options...
atbarr Posted September 5, 2009 Share Posted September 5, 2009 I had a similar problem, it was very cloudy and a light rain. I went back the next day and the results were much better. As far as muzzle blast, that means you might have been too close to the chrono.A.T. The skies were clear. Maybe I should back up further? Around 20 feet or so just to see if I'll get consistent readings? IMO, 20 feet is too far. A.T. Link to comment Share on other sites More sharing options...
Will_M Posted September 5, 2009 Author Share Posted September 5, 2009 (edited) IMO, 20 feet is too far.A.T. I just want to be sure the chrono can take consistent readings. So from the muzzle to the first fork of the chrono, you'd suggest around 12-14 feet? Edited September 5, 2009 by Will_M Link to comment Share on other sites More sharing options...
atbarr Posted September 5, 2009 Share Posted September 5, 2009 I think it's closer to 10' A.T. Link to comment Share on other sites More sharing options...
Jman Posted September 5, 2009 Share Posted September 5, 2009 IMO, 20 feet is too far.A.T. I just want to be sure the chrono can take consistent readings. So from the muzzle to the first fork of the chrono, you'd suggest around 12-14 feet? Yes, 12-14' is fine. By muzzle blast I mean the particles in the blast that may reach the sensor and be recorded before the bullet. The bullet passes over the sensor AFTER the blast recording causing bad readings. Jim Link to comment Share on other sites More sharing options...
atbarr Posted September 5, 2009 Share Posted September 5, 2009 IMO, you should ask the manufacturer of your chrono. Just google their name. A.T. Link to comment Share on other sites More sharing options...
Will_M Posted September 5, 2009 Author Share Posted September 5, 2009 It says that with anything fired sub sonically, the muzzle blast will definitely interfere. I'll try varying distances, with known velocity ammo first. Keep the suggestions coming. Link to comment Share on other sites More sharing options...
G-ManBart Posted September 5, 2009 Share Posted September 5, 2009 IMO, 20 feet is too far.A.T. I just want to be sure the chrono can take consistent readings. So from the muzzle to the first fork of the chrono, you'd suggest around 12-14 feet? Yes, 12-14' is fine. By muzzle blast I mean the particles in the blast that may reach the sensor and be recorded before the bullet. The bullet passes over the sensor AFTER the blast recording causing bad readings. Jim +1 I've had good luck using a Chrony at 15ft. Even bullet setback isn't likely to cause 100fps difference in actual velocity. One time we set up my Chrony in front of my friend's CED and the two units were within 10fps of one another....consistently with several different guns and loads. If I remember the CED was 10fps lower, but there's no way to know which unit was actually "right". The fact that the difference stayed consistent tells me both units were probably very close to the real velocity. The other thing that can cause huge swings like that is direct light glaring on one of the sensors. In the shade on a bright day works well, overcast, but light days work the best and if you can't get either of the above, use some cardboard on the sides of the skyscreens to keep direct light off the sensors. If the sun is high a target turned upside down (white side facing sensors) on top of the screens will also help a lot. R, Link to comment Share on other sites More sharing options...
XD Niner Posted September 5, 2009 Share Posted September 5, 2009 (edited) I use my Shooting Chrony at about 15 feet as well and have good results. One trick I've learned is to place a new target with the white side down on top of the screen support rods rather than use the screens. This seems to provide a much better and more consistent background for the sensors. The other procedure I follow is to place a bulls-eye target a couple of feet behind the chrono. I position the bulls-eye right where I want the round to go. For me that is between 4 and 6 inches above the sensor. This gives me the ability to put all rounds over the sensors at the same height within about a half inch either way. I'm just trying to reduce all the other variables. Edited September 5, 2009 by XD Niner Link to comment Share on other sites More sharing options...
Jman Posted September 5, 2009 Share Posted September 5, 2009 These are all very good suggestions. Will. Let us know if you are seeing different results. Jim Link to comment Share on other sites More sharing options...
Genghis Posted September 8, 2009 Share Posted September 8, 2009 A while back I had some significant velocity variations with .38 Super. I tried a bunch of stuff but nothing helped. Finally I figured out that some of the brass I was using was so thin that it wouldn't hold the bullet in place. I think when it fed into the gun, it pressed the bullet back onto the powder, and the lower volume in the casing increased the pressure. Link to comment Share on other sites More sharing options...
Will_M Posted September 15, 2009 Author Share Posted September 15, 2009 (edited) UPDATE: I put my chrono in the shade, paced off 14 feet, fired the exact same load and voila! The results speak for themselves. String #1: #1: 1023 fps #2: 1020 fps #3: 995.5 fps #4: 1009 fps #5: 991.7 fps #6: 1002 fps There was still the extreme spread of 32fps. But I consider that acceptable. Thanks for all the advice gentlemen! I had no idea having the chrono out in the direct sunlight would have such a dramatic effect. Edited September 15, 2009 by Will_M Link to comment Share on other sites More sharing options...
relictrader Posted September 16, 2009 Share Posted September 16, 2009 Attended a Steel Match last month where a number of Master shooters were using 9mm , 3.8gr Solo 1250 with 160 gr Molly RN bullets, OAL 1.70(on Lands) and making power factor with very mild recoil. I was impressed with preformace from these 9mm on steel popers that had to be knocked down before other targets would be presented. I tried this same load and found that barrel jump was minium ,but tight crimps seemed important in order to make consistant PF numbers? Link to comment Share on other sites More sharing options...
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