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Crono readings?

This is a discussion on Crono readings? within the Reloading forums, part of the Ammunition category; Guy's this may be an obscure question here but I have been wondering... Here for a few times out with my rifle and reloads my ...


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Old May 22nd, 2020, 07:29 PM   #1
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Crono readings?

Guy's this may be an obscure question here but I have been wondering...
Here for a few times out with my rifle and reloads my friend Bill has gone out with me...
We are shooting the same rifle and the same reloads but HIS crono numbers always seem to be better than mine?


Does body mass and recoil control have any effect on ES and SD?


Or are we just in the normal range...?


Still I have the question

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Old May 22nd, 2020, 07:34 PM   #2
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maybe he’s placing his shots more consistently thru the screen opening.

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Old May 22nd, 2020, 07:39 PM   #3
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maybe he’s placing his shots more consistently thru the screen opening.

No idea Douglas but he is a good shot...


I asked him the same question last time out and he told me I was crazy...lol


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Old May 22nd, 2020, 10:00 PM   #4
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JEFFJP_N_JJ,

Chrono readings can be influenced by a few factors, if he is shooting at a more consistent pace then you then the round isn't getting hotter in the chamber as yours may be if you are shooting at a more random pace. This is also one of the reasons you don't want your ammo sitting in the sun. When shooting long range if I can't break the shot in my normal shooting pace I'll remove the round and load a different one, ammo sitting in a hot chamber will "heat soak" and it will affect velocity. This in turn will affect trajectory. As to the question of body mass and recoil control influencing ES and SD, I don't believe they could have any affect, they could however affect grouping just as trigger control and follow thru will.

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Old May 22nd, 2020, 11:43 PM   #5
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I was taught to "hold hard" on the rifle, meaning pull it in to your shoulder and hold it very firmly. In advanced rifle class I saw the variances of inconsistent holds with 2 chronometers set up. I can't explain the science completely, but I think if one guy holds very hard it has resistance and the velocity will be slightly differently than a guy holding lightly and the rifle will not have as much resistance while the bullet has traveled through the area where the chronometers are. That's one reason why consistency in hold is important, but it really shows up more at long range.
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Old May 23rd, 2020, 05:03 AM   #6
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Just how much different are they ?

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Old May 23rd, 2020, 05:24 AM   #7
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thesurvivalshop asked a good question.
I would like to see the data. How different are they? Was it a one rep test? Or an extended test?
I could have been that what you saw was variation that would occur in an extended test but in an extended test - the averages may not be different. Cant say without repeating the test exactly.
The cadence of fire, and chamber heating - if different - could well be part of the explanation

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Old May 23rd, 2020, 07:55 AM   #8
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Don't forget that most commercially available chronographs have an error range of something like plus or minus 30 FPS so when you compare velocities the numbers mean very little unless you see at least 40 or more FPS difference.

In theory, hold changes velocities due to the muzzle position changes, not because of actual bullet velocity changes. In other words, if the rifle butt is pulled tighter into your shoulder then the muzzle will be pulled farther from the chronograph which increases the distance that the bullet travels before it reaches the chronograph which results in the bullet moving at a slower velocity when the chronograph measures it's speed. But unless you are using a very expensive lab grade radar system you aren't going to get any reliable data. If you shoot a lot of ammunition you might see an average trend one way or another but you won't be able to assess the effect on every shot with any confidence.

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Old May 23rd, 2020, 09:34 AM   #9
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JEFFJP_N_JJ,

I've attach a page from my Oehler 33 chronograph manual, it's a pretty interesting read on comparing SD's. For instance if you take load A SD of 10 for 10 shots, load B has to have an SD of greater than 18 to say that load A is the most uniform. The same can be said for the same load shot at different times/temperatures during the day. Shoot load A at 08:00 and the shoot it again at 13:00, load A could have been shot when outdoor temp was 65* and then the second time when it was 85-90*.

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Old May 23rd, 2020, 09:57 AM   #10
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If I understand the question correctly...

You and your friend are using the same rifle, same ammunition, same chronograph, on the same day.

The only variables are body size/weight and shooting technique.

His ES and SD are smaller than yours.



Factory ammunition is usually tested on a device similar to the one below. So yes, I would think any variable would produce different numbers. My brain tells me that the more you stabilize the rifle, the smaller the ES and SD.
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Old May 23rd, 2020, 12:02 PM   #11
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Machine Rests will show more consistent results , because you take the Human factor away from the equation .

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Old May 23rd, 2020, 04:24 PM   #12
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Quote:
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Just how much different are they ?

Not very and I told Bill they are in the ES/SD area? But they ARE different!

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Old May 23rd, 2020, 04:27 PM   #13
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Quote:
Originally Posted by RAMMAC View Post
Don't forget that most commercially available chronographs have an error range of something like plus or minus 30 FPS so when you compare velocities the numbers mean very little unless you see at least 40 or more FPS difference.

In theory, hold changes velocities due to the muzzle position changes, not because of actual bullet velocity changes. In other words, if the rifle butt is pulled tighter into your shoulder then the muzzle will be pulled farther from the chronograph which increases the distance that the bullet travels before it reaches the chronograph which results in the bullet moving at a slower velocity when the chronograph measures it's speed. But unless you are using a very expensive lab grade radar system you aren't going to get any reliable data. If you shoot a lot of ammunition you might see an average trend one way or another but you won't be able to assess the effect on every shot with any confidence.

Bill IS a good shooter and I do see him trying to get the rifle back to the same starting position as I try to as well...

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Old May 23rd, 2020, 04:35 PM   #14
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Thanks guys! You ALL are great!


Bill IS a good shooter but he does not always out shoot me... Making me wonder though as to what else there is to learn... Thanks John!


Last edited by JEFFJP_N_JJ; May 23rd, 2020 at 04:39 PM. Reason: added info!
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Old May 23rd, 2020, 04:59 PM   #15
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https://m14forum.com/ammunition/5046...5-10-20-a.html

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