Help with chrono readings needed

[pops1982]

Went to the range yesterday to chrono a load I'm working up. It was a partly cloudy sunny day and the sun was almost straight overhead. I assume this is not the best conditions for chronographing. I shot the first 24 rounds with the chrono pretty much level and the average fps was 1126. At that point I tilted the chrono just a little bit so that the difusers would cast a shadow on the openings of the chrono that do the reading and the average fps of the next 25 rounds dropped by 56 fps. I'm wondering if the reading with the chrono level and the openings not in a shadow are best or would the readings with the chrono tilted just a bit so that the diffusers cast the shadow on the openings are best. And then maybe I need to rechrono anyway on a day or time of day with better conditions.

The first set of readings made PF (129) and the second set did not (123).

Thanks for your help.

[Jonathan Taliani]

I'm not sure which results are more trustworthy, but I would definitely rechrono either way.

[Youngeyes]

What chrono are you using? What was the SD? It will also make a difference how high you shoot over the sensors. I keep the shot in the upper third of the sensor area. I also use an LED light setup indoors and out. It helps stabilize the readings.No way to know which are good readings from the description. When you loaded those rds what were you expecting? Which is more likely, the 1126 or the under 1100 readings? I would stabilize your lighting and shooting conditions before I accepted the readings as final.

[Hi-Power Jack]

the first 24 rounds average fps was 1126. next 25 rounds dropped by 56 fps.

Pops, how large a range did you get on the 1st and 2nd groups?

My guess is that the first group was 1060 - 1180, or so??

I've seen myself, and in a posting here a few months ago, that for some

reason, it's not uncommon for the velocity to "drop" as you keep shooting

thru the screens? Barrel heat?

I'd definitely try it again, but wouldn't be too surprised if you got

very similar results.

I'd make sure the LOWEST velocity cartridge had a power factor of 125.1

or a little higher - probably average around 130 - 132.

Good luck,

[pops1982]

What chrono are you using? What was the SD? It will also make a difference how high you shoot over the sensors. I keep the shot in the upper third of the sensor area. I also use an LED light setup indoors and out. It helps stabilize the readings.No way to know which are good readings from the description. When you loaded those rds what were you expecting? Which is more likely, the 1126 or the under 1100 readings? I would stabilize your lighting and shooting conditions before I accepted the readings as final.

This very one:

http://www.brianenos.com/forums/index.php?showtopic=157157

[pops1982]

the first 24 rounds average fps was 1126. next 25 rounds dropped by 56 fps.

Pops, how large a range did you get on the 1st and 2nd groups?

My guess is that the first group was 1060 - 1180, or so??

I've seen myself, and in a posting here a few months ago, that for some

reason, it's not uncommon for the velocity to "drop" as you keep shooting

thru the screens? Barrel heat?

I'd definitely try it again, but wouldn't be too surprised if you got

very similar results.

I'd make sure the LOWEST velocity cartridge had a power factor of 125.1

or a little higher - probably average around 130 - 132.

Good luck,

out of the 1st 26 only 2 were below 1100 (1084 & 1097). Then I tilted the chrono as describe to move the shadows of the diffusers over the reading slots and then out of the next 23 rounds only 1 was over 1100 (1106).

[Steve L]

I loose velocity by leaving my ammo in the sun. my powder is reverse temp sensitive, did you rule that out?

[pops1982]

I loose velocity by leaving my ammo in the sun. my powder is reverse temp sensitive, did you rule that out?

I dont think thats it because the readings were consistantly in the mid 1100's until I tilted the chrono as described and then after that they were consistanly in the mid 1000's. All of the readings were taken in 30 minutes or less.

[Hi-Power Jack]

I still bet that if you try it again, and leave the chrono in same position,

that you'll get the 1st 24 shots higher than the last 24 shots

Be interesting to see - can't wait to hear your results.

I'd still put enough powder in there that all 48 shots are above PF125.

[Sarge]

I put velcro on top of the diffusers and velcro on 2X2 white plastic sheeting. When the conditions are too bright I put the lid on it. This gives you the preferred white cloud cover type conditions. Works very well and always very consistent. Pro Chrono Digital.

[pops1982]

I put velcro on top of the diffusers and velcro on 2X2 white plastic sheeting. When the conditions are too bright I put the lid on it. This gives you the preferred white cloud cover type conditions. Works very well and always very consistent. Pro Chrono Digital.

Great idea. That's what I'm going to do.

[pops1982]

I still bet that if you try it again, and leave the chrono in same position,

that you'll get the 1st 24 shots higher than the last 24 shots

Be interesting to see - can't wait to hear your results.

I'd still put enough powder in there that all 48 shots are above PF125.

Don't thinks but I will try it and we will see.

[Skydiver]

Not only do you have a chrono, now you also have a kite! Two for the price of one!

[pops1982]

Not only do you have a chrono, now you also have a kite! Two for the price of one!

skydiver, these days we have to make every spent dollar count.

[SLM]

How did you "tilt" the chrono? Side to side or front up/down? You need to have the sensors as much in a straight line with the bullet travel as possible. Having the sensors tilted up/down in relation to the bullet path essentially changes the distance between them.

Up/down would usually show a higher fps but you may not have been level to start with.

[pops1982]

How did you "tilt" the chrono? Side to side or front up/down? You need to have the sensors as much in a straight line with the bullet travel as possible. Having the sensors tilted up/down in relation to the bullet path essentially changes the distance between them.

Up/down would usually show a higher fps but you may not have been level to start with.

It was pretty much level when I started and when I tilted it I raised the front .5" - 1". I really think it was this that caused the change in the average fps and not the shadows being moved over the sensors.