haugenna

I went to the range three times last week and shot over a chronograph. I shot the same load on Monday as I did on Friday and Saturday. All days were calm days, 60-70 degrees and I pushed a 200 Gr TSX 3292fps was avg, hi 3301, lo 3284, with 100 Gr. RL 25.

I went back Friday and Saturday and only achieved 3170 avg. One thing I did learn, is that most reloadingbooks are full of it when they talk about powders and velocity. What could have been the factor? Any advice. Primers, bullet, powder were all the same. Does trim length and bullet seating depth make that big of a difference? COL was 3.777 on Monday and Saturday and 3.770 on Friday. All shots were with warm, not hot but not cold, barrels. Does ten degrees temperature make that big of a difference? Any advice would be helpful.

stubblejumper

Bullet seating depth and temperature will effect velocity but in both cases the differences are too small to make that much difference.Were the powder ,primers and bullets from the same lot #s on both days?How were the light conditions on both days?Some chronographs are effected by lighting conditions.It may seem silly,but is your chronograph a chrony?I have witnessed someone using one that wasn't totally opened up to the stops.The result is noticeably higher readings.

haugenna

Stubble,
All bullets, primers and powder came from the same can, box, and tray. I am shooting over the gamma master. Monday was sunny without sun shades on the chrony, Friday was later in the day, a little sun on the chrony and no shades, Saturday, sunny with sun shades.
"Opened up to the stops" what does that mean? Would the sun shades on during a sunny day give me the same readout as sun shades on during a cloudy day?

haugenna

Stubble,
"open to the stops" think I got it, The chronograph completely opened up.

trailer

You said it but I did come across a couple of loads that were bang on with the loads in books...

bigcountry

I have same issues with my pact and chony F1. What I found was light conditions was the dominating factor. But it doesn't make sense.

I shot over a friends oehler and it was rock solid one day as it was a year before that. You get what you pay for in chronys.

I like you starting suspecting weather and all. But did the tape test. I put clear tape over my sensors to see what would happen. I lost velocity. By 100fps. Sometimes more.

So I started experiementing taking one peice off the front and so on.

I am a EE, so know little something about timers, and photocells. One thing I do know is temp has a big effect sometimes on circuits. But I am having a hard time wrapping my arms around this problem. Light is light, so theorectically, it shouldn't make a difference on timing no matter how cheap the components are for a F1 or Gamma, or whatever. So I conclude it has to be with the timer circuitry. Any of you guys who have went thru physics or Engineering program has probably has to build a crude timing source from a Quartz timer or something and know you can adjust timing by a few factors but not by much.

thndrchiken

Did you clean your barrel inbetween range sessions? A clean bore will sometimes reduce velocities until it's gets fouled, then the velocities start to come back up.

stubblejumper

If you don't use the sun shades on a sunny day,you willoften get high readings with the chrony.As such,I believe that the readings that you obtained on the second and third day are probably more accurate.

Solitary Man

As the owner of a Shooting Chrony myself, I tend to agree with stubblejumper.

haugenna

Stubble and Solitary,

Thanks for the info....As a new owner of a chrony....I need to make sure it is completely open and that I have the sun shades on at all times.

Haugenna