I get some odd readings using coated bullets when shooting over an optical chronograph. Rifle is a 270 win with 22" barrel. Shooting a Nosler 140g AB that is coated with a black coating and red tip, from shooters pro shop. Using IMR4831 powder, Nosler data for this bullet weight shows a max of 53.5g @2910fps. Middle load is 51.5 @2790fps. I have an accurate load with 52g but velocity is only reading 2500-2550. I did not have a chrono when putting this load together. Is the chrono reading off because of the coated bullets? I do have some regular uncoated 140AB bullets so next step is loading a few with same load and chrono them.
Coated bullets and optical chronographs?
- Thread starter Philward
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I would think that those velocities are good. I have a 22" barreled Browning BBR 270 Win. With the 140 gr Sierra my load is 57 grs IMR 4831 and vel is 2822 ft/sec. 52g would be a very mild load in my rifle. JME
Just checked my notes and see where I used 52g of IMR4831 with a 150 gr Sierra, Velocity was 2577 ft/sec. Seems to match up somewhat with your load..
Just checked my notes and see where I used 52g of IMR4831 with a 150 gr Sierra, Velocity was 2577 ft/sec. Seems to match up somewhat with your load..
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Mikecr
Well-Known Member
Which chrono?
Some are passive and see a dip in light, some are active to cause a reflection
Some are passive and see a dip in light, some are active to cause a reflection
MagnumManiac
Well-Known Member
Do you use the diffusers? If you don't, the shadow may be being missed.
Have seen those chrony's behaving strangely several times, most often it was the time of day for the cause.
Cheers.
Have seen those chrony's behaving strangely several times, most often it was the time of day for the cause.
Cheers.
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Are you sure it's set up perfectly level? That can cause false readings.
This! This is just one of the few frustrations with my old Crony (I glued a level and laser light on it). I still have it, though, and it works (backup).
Flatbow
Well-Known Member
Sun and clouds can effect them as well.
If I remember correctly mine worked best on an overcast day with no sun break throughs. Or all sun and no shadows
If I remember correctly mine worked best on an overcast day with no sun break throughs. Or all sun and no shadows
std7mag
Well-Known Member
One thing I found with my Beta Master was the muzzle blast was messing with it.
Backed the chrono off another 5ft and no issues.
Backed the chrono off another 5ft and no issues.
While some may think that the color of a bullet should not matter, when it comes to using a radar type chronograph it may. Radar uses reflected signals in order to determine time, distance and speed. Shiny things, cars, aircraft and bullets will reflect the radar signal back much more reliably than a dark/flat object. You may note that most military aircraft, especially those of stealth design all have dark or flat finishes. This is because the radar signals are absorbed or the reflection decreased to keep radar from picking them up. In my sometimes muddled mind, it seems that it would work the same on bullets. Shiny bullet, good reflection, dull bullet limited or no reflection. Anyone else have thoughts on this?
I didn't use a level it was set pretty flat, I did use the diffusers. and the weather was 60's and partly cloudy to cloudy. The other rifles I was shooting read pretty much what was normal, a 25-06 with 100g E-tip at 3000 fps just working up a load so this was still a lower charge and a 280rem with 150 E-Tip at 2725. And for the 270 140 nosler data the starting load is 49.5 at 2670fps.
azarcher10x
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I never had any issue with the same chronograph. I would recommend buying their plexiglass shield that will protect it from dirt and dust...and muzzle blast. Without the shield, I can shoot my 300 RUM through it, just a couple feet in front without issue, but it's braked. Tried that with a buddy's 300WM unbraked, and had to reassemble the chronograph!
I do think there is a something to the color, or reflectiveness of the projectile. I have had issues on occasion getting it to read completely blacked out arrows.
I do think there is a something to the color, or reflectiveness of the projectile. I have had issues on occasion getting it to read completely blacked out arrows.
Critter Picker
Well-Known Member
I have the same chronograph, was shooting moly coated Sierra GK out of my .243 without any problem. They are a blue color if that matters.
MagnumManiac
Well-Known Member
Optical chronographs work by the bullet casting a shadow, they do not need a reflection of any kind to operate. If the shadow is not directly above and centred in BOTH screens, it will give false readings.
They actually work best on overcast days because the light is dull and the shadows are sharp.
Cheers.
They actually work best on overcast days because the light is dull and the shadows are sharp.
Cheers.
