Higher velocity on chronograph than reloading manual

[Seeking_Coyotes]

Borrowed a friends chronograph to get the speed of my load for a turrent I'm having made for my Burris C4. First time using a chronograph. Set it ten feet in front of the gun and it was cloudy outside. Results pretty consistent but the chrno was coming in at 3300 and the Hornady maual has in it 3000. Which do I trust for getting the turret made?

Load is .243 70 SMK w/ starting load of Varget...book says 3,000 velocity.

 

[FroggyOne2]

How long is your bbl vs the one in the data used in the book. I believe most company's use a 24 inch test bbl for their data. You could simply have a fast bbl. If your not getting any pressure signs of any kind, I wouldn't worry about it.

 

[GaryCrow]

Move it to about 15' from the muzzle, you could be getting muzzle blast across the sensors.

 

[wyoming .260]

If the chronograph is the flip open variety make sure it is open completely flat. as any tiny change in angle will give you faster speeds then real life. The chrony people say if not fully open, say less then 1 degree of angle will add 75-80 fps. had a tripod quick detach mount on one and it added maybe two degrees of angle and 150 fps to previously tested speeds........

 

[fredhorace77]

Borrowed a friends chronograph to get the speed of my load for a turrent I'm having made for my Burris C4. First time using a chronograph. Set it ten feet in front of the gun and it was cloudy outside. Results pretty consistent but the chrno was coming in at 3300 and the Hornady maual has in it 3000. Which do I trust for getting the turret made?

Load is .243 70 SMK w/ starting load of Varget...book says 3,000 velocity.

i would double check your chrono to another model...or also shoot another type of firearm thru it with a some what known velocity...i always use a .22lr for double checking my chronos...always reads about 1080 fps out of my 22lr and then i go to the big gun to see what it says...considering that your having a turret made i would double check first...no sense in wasting money on the turret to have to have it remade again if you were wrong

 

[jonbearman]

Are you supposed to shoot level across the screens?Meaning the barrel is perfectly level with the chronograph or just fairly close?

 

[TheSnake]

Are you supposed to shoot level across the screens?Meaning the barrel is perfectly level with the chronograph or just fairly close?

If you are looking for consistency in speed from shot to shot then I don't think this matters. If you are looking for a true reading of actual velocity, than I think this makes a difference. The further you move away from level, the further the bullet has to travel to break the barriers and the slower your reading will be. With the screens being so close together, a little bit can make a difference.

Did a quick search and yes I am correct.

http://precisionrifle.wordpress.com/2012/07/20/chronograph-tips-15-practical-tips-to-increase-accuracy-reliability/

 

[brian427cobra]

I don't trust Chrony brand chronographs, if your a Reloader I suggest buying your own, as for the Turrets, they look cool on TV, but in the real world they don't work, how often is the Density Altitude(temp baro humidity altitude) the same as what the turrets are calibrated for? Answer is never.

 

[Rustystud]

I own 5 chronographs and none display the same velocities on simultanious shots.

Nat Lambeth

 

[wboggs]

You can't too compulsive with the exact number on these inexpensive chronographs. You are looking for a relative value. Having said that, they are vast improvement when only the factories and testing labs had access to these . I still remember Weatherby claims for 3400fps with a 180 gr in the .300 Wby using a 26" barrel. As they say, we've come a long way, baby.
Bill

 

[Lapua40X]

...
Did a quick search and yes I am correct.

http://precisionrifle.wordpress.com/2012/07/20/chronograph-tips-15-practical-tips-to-increase-accuracy-reliability/

Great tech. info. Thanks for the link.

 

[Seeking_Coyotes]

Move it to about 15' from the muzzle, you could be getting muzzle blast across the sensors.

I'll try it. I was so afraid of shooting the chrongraph. Just tried to eyeball it at ten feet.

 

[Seeking_Coyotes]

How long is your bbl vs the one in the data used in the book. I believe most company's use a 24 inch test bbl for their data. You could simply have a fast bbl. If your not getting any pressure signs of any kind, I wouldn't worry about it.

I have a Savage Model 10 Predator Max 1 with the 24" fluted barrell.

 

[Seeking_Coyotes]

If the chronograph is the flip open variety make sure it is open completely flat. as any tiny change in angle will give you faster speeds then real life. The chrony people say if not fully open, say less then 1 degree of angle will add 75-80 fps. had a tripod quick detach mount on one and it added maybe two degrees of angle and 150 fps to previously tested speeds........

Had no idea about this. It is a flip open model and I think it was flat on the tripod top. What if the V in the front and back are not square to the target exactly? Does this give a false reading?

 

[wboggs]

Anything that alters the distance between the star and stop screens changes the velocity reading. The screens should be perpendicular to the shot, as much as possible.
Bill

 

[rardoin]

I would also consider firing groups at distance intervals so you can see the actual external ballistics on your setup. You can back calculate MV from this data and compare to the chrony. If I were to have a custom turret made I certainly would measure the actual drop at 100, 200 and 300yds first. JMHO

Robin

 

[wboggs]

Also, how does the custom turret account for changes in temperature, humidity, altitude, etc. ? You will have to fire your load to get drop figures at far beyond 300yds if you want it for long range work. Sounds like they be overrated to me.
Bill

 

[Seeking_Coyotes]

Amazing the chronograph is 100 fps slower on a clean barrell. Also shot is a good half inch outside the group on first shot on a clean barrell.

 

[Seeking_Coyotes]

I would also consider firing groups at distance intervals so you can see the actual external ballistics on your setup. You can back calculate MV from this data and compare to the chrony. If I were to have a custom turret made I certainly would measure the actual drop at 100, 200 and 300yds first. JMHO

Robin

Robin...if you would be willing to help me double check the chronograph through your method please send me a pm and I can get the drop figures this weekend out to 300 yards.

 

[brian427cobra]

http://www.jbmballistics.com/ballistics/calculators/calculators.shtml