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Confusing chrono results today.

767 views 13 replies 11 participants last post by  jdw174 
#1 ·
I'm new to chronographs. I fired three different loads of 45/70 through my rifle, some cowboy and hand loads through my rifle and revolver, some Remington and hand loads through my g20, some .380 through my ppk, and some herters 9mm through my p938 and walther ccp . The results were about what I had expected them to be.
Then I fired some american eagle 130gr .38 special through my S+W model 60 and my Ruger Match Champion. The snubie averaged about 760fps for a 10 shot string and the gp100 averaged about 876fps for a 10 shot string, again no surprise.
Here is where I get confused. Next I fired herters .357 158gr fmj through the snubie and averaged 1367fps for a 10 shot string. Heavy recoil. After writing that string down I fired the same ammo out of the same box through the gp100 averaging 1149fps for a 11 shot string. After the first shot (1120fps) I thought that can't be right,it must be an error! But then all the remaining shots were in the 1100's too.
Does anyone have a theory as to what's going on? And No I did not mix up the results. I fired the snubie wrote down the results and then fired the gp100 and wrote those down.
 
#3 ·
This post may be on to something. A difference in the amount of powder between rounds is the first thing I can think of. It's just a weird coincidence that it happened when you switched guns.

Just out of curiosity, you might put a micrometer on the bullets and see if the Herters isn't a thousandth of an inch oversized. .... if the GP 100 has a slightly tighter bore .....
 
#8 ·
the muzzle was 10 feet from the chrono, I had a tape measure laying on the ground. As I said before, I did not mix up the numbers, the ammo was from the same box and the fps mps setting was not changed between strings. I don't know if different chamber or force cone/bore demmlsions would account for the strange readings or what is going on.
 
#9 ·
the muzzle was 10 feet from the chrono, I had a tape measure laying on the ground. As I said before, I did not mix up the numbers, the ammo was from the same box and the fps mps setting was not changed between strings. I don't know if different chamber or force cone/bore demmlsions would account for the strange readings or what is going on.
I bet the snubby did not achieve those velocities, even if the cylinder was welded to the barrel, and the barrel was a perfect fit to the round :)

But a retest of that snubby and that ammo would be interesting!
 
#11 ·
Most chronographs say a MINIMUM of 10 feet. I usually about 15 feet or so. I would guess too close/ muzzle blast.

wp
 
#12 ·
Keep in mind, a chrono just "looks" for a small change in light from a photosensor. It detects when light decreases.

They are not perfect measuring devices and (for most consumer models) have no error detecting capability. So it is possible to get strange readings.
 
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