wierd velocities, Load or chrono problem?

coldmaker

coldmaker

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hello all!

i started load development for my wife 260 rem model 7 this morning.

i use remington once fired brass
cci br 2 primers
nosler 120 gr. ballistic tips
and h4350 powder
coal is 2.780"

i tried the newberry method for the first time. as far as grouping goes
i'm satified, for a first attempt.
here's the target.


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group number three has a flier, probably my error, i just don't know.

so here's the chrono i got on those
group 1 is 44.8 grains vel. was 2744,2789,2005???
group 2 is 45.2 grains vel. was 2803,1969,1766
group 3 is 45.6 grains vel. was 2772,2002,2650
group 4 is 46.0 grains vel. was 1999,2063,2715
group 5 is 46.4 grains vel. was 2054,2867,2825.

i also shot 3, 3 shot group with my 308 and factory loads, and all were around 2700 fps.
so what do you long time reloaders think?
i never experienced something like this with this chrono so far.
after the first few odd readings i relocated the setup somewhere else
to make sure the sun angle wasn't playing tricks on the chrono.( prochrono pal)
all the loads were carefully weighted on a beam scale.
scale was zeroed before and checked after loading session.
all the shot felt the same (recoil and muzzle blast).
should i use magnum primers with this powder?

is it possible that it's the load?
wouls i get groups like that at 100 yard with some bullets going 800 fps slower?

i'm a bit lost right now.
thank's for your help.
 
Seems like a bright sun, no diffuser problem to me. Sunlight reflecting off of bullets is not good for chronograph accuracy. Use you diffusers or shoot under cloudy skies, and I predict your "problem" will go away.
 
what were the lighting conditions over the chrony at the range?


Your groups don't seem to indicate such a variation in velocity. I'm leaning towards the chrony.
 
conditions were sunny. but at such an angle that the diffusers were not shading the sensors.
i'll try again in cloudy weather.
 
A friend and I were having similar problems with his in bright sun (though not that dramatic) so we ended up finding a material that was like corragated cardboard but translucent (check your local craft store) and attaching it on top. Works like a hot damn, well at least till the wind catches it!
 
I made a box for my chrony. Approx 30" square and left the top open and placed a sheet of diffused ceiling tile light cover over it. Place chrony in box and shoot through the open ends. I've haven't had any issues with velocity readings since. I use a Shooting Chrony F-1.

-Jason
 
coldmaker said:
conditions were sunny. but at such an angle that the diffusers were not shading the sensors.
i'll try again in cloudy weather.
Click to expand...

POTP right here. Sensors should be shaded by the diffusers. Also, what was the distance between the muzzle and the screens? Should be 15 ft or so or else the muzzle blast can make for erratic readings. If problems persist, try moving your chrono a few more feet down range.
 
thanks guys
chrono was at 15 feet at first and i moved it to 30 yard for the last 5.
but it's probably lighting conditions then.
so i'll try again with the same load in cloudy condition for fun.
 
I've finely retired my old Chrony Beta after years of mostly good service.. great if overcast. The range I shoot at lately has an overhang that casts an odd shadow across where the Chrony should be which also has been causing problems. After coming home lately with odd velocity readings, and frustration with my old Chrony I decided to buy a CED MII with IR screens... time will tell if it makes a difference.
 
I may be wrong but I think the shades aren't actually designed to shade the sensors from the sun but rather provide contrast between the bullet and it's backing.
 
I have been to the range a few times now with a fellow that bought the L E D light system for his Chrony. Matters not what the ambient light is doing with this set up, works so darn slick I'm going to get one myself. FS
 
Taylor-Made said:
I may be wrong but I think the shades aren't actually designed to shade the sensors from the sun but rather provide contrast between the bullet and it's backing.
Click to expand...

Yep, which it can't do with direct sunlight reaching the sensors, hence the shading, not for shade's sake, but to provide the diffused light background against which the sensors can "see" the bullet.


I have been to the range a few times now with a fellow that bought the L E D light system for his Chrony. Matters not what the ambient light is doing with this set up, works so darn slick I'm going to get one myself. FS
Click to expand...

My CED came with these. Mine still won't work if bright sunlight falls directly on the sensors but, with the UV light, you just lay a piece of cardboard box, large enough to span the screens, across the top of the screens. This shades the sensors from the sun and the UV light lets em "see". These lights also work in dark conditions and indoor ranges quite nicely.
 
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