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Posted: 5/4/2011 7:46:03 AM EDT
| Hey all. I was at the range this morning checking fps over my chrony. It was overcast so i did not need the sky screens. Put the sky screen posts in for visual poa. Using a sand bag rest i proceeded to fire 20 rds of 9mm ammo. Average fps was 875. I then stood straight up and fired another ten shoots over the chrony. This is where i am confused. I thought the chrono measured the time it takes for the bullet to pass over the first sensor and then over the second one. Well it seems that using the same load but shooting maybe 3 feet higher thru the posts my fps averaged 940. Does this seem strange. |
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What type of chrony? I have never shot without the sunscreens so I don't have anything to compare your results with.
If your loads were identical I would imagine it could be the sensors in the chrony not being parallel with each other. It would seem they could be leaning toward each other just a touch so that the higher up you shoot, the closer the beams are which would result in a faster fps. Not an expert but throwing that out there. Can you borrow a chrony to compare with? |
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Quoted:
If your loads were identical I would imagine it could be the sensors in the chrony not being parallel with each other. It would seem they could be leaning toward each other just a touch so that the higher up you shoot, the closer the beams are which would result in a faster fps. Not an expert but throwing that out there. Yes. You need to shoot over both sensors level. I discovered that last weekend. I had 2 targets up at 50 yards, one above the other. The top target put the bore level over the sensors. The bottom target gave it a slight angle of a few degrees. I didn't think it would give such a drastic difference, but the chrony was reading +500 fps (imagine my surprise seeing 175gr SMK going 3060 fps with just 42.0gr of W748). |
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