Chrono speeds

[orchemo]

I have used two chronos over the past year. I seem to get results about 150-200 fps slower than the Nosler test load data. I typically set the chrono about 15 feet in front of the muzzle.

The Nosler data is from a test barrel? Presume a longer barrel than the typical hunting barrel? Do they measure from the tip of the barrel or a specific distance in front of?

While not too worried about velocity, as long as it shots. I find it interesting.

Thanks

 

[SJB358]

Same here Eric, I have rarely found Nosler data to be the same as what I get out of my rifles given the same charge.. Some of their data seems odd, as I have never seen 63 grains of RL22 give 3000FPS with a 160 anything.. 66-67 yes, but never 63..

Same for their 270WSM loads, but the chrono does help and their powder choices are pretty spot on as far as I am concerned. They will produce the speed in most of them, just takes a little more in most rifles.

 

[DrMike]

Note that Nosler lists muzzle velocity. Extrapolate back and you will approximate listed velocities. Also, you must allow for variation in chamber dimensions and adjust for barrel length.

 

[orchemo]

Thanks Mike. That was my thoughts, just had not taken the time to calculate velocity back to the muzzle

 

[Jimbeaux82]

so if you set a chrono approx 15 ft from the muzzle, what correction would you use to get MV?

 

[orchemo]

Found a formula for those interested

http://www.longrangehunting.com/forums/ ... ity-61081/

 

[Wincheringen]

I did get the same published velocity as the book for my 280 with RL22. I was a little surprised since their test was with a 24" barrel and mine is a 22". I could probably try a different chronograph but as long as it makes it out of the barrel and pokes some holes down range that is good enough for me.

 

[orchemo]

I also used the ballistic app on my phone and adjusted the increments to 5 yds, then played with the muzzle numbers until I had measured speed at 5yds.

 

[Antelope_Sniper]

If you set the chronograph at 15 feet, add 8 FPS to the reading to get actual muzzle velocity. In other words, the differenece is withing the margin of error, and not worth worring about.

Now that you've started chronographing you will begin to see all the factory that can affect your velocity.

With the same bullet and powder, you can vary 100 fps by changing primers and another 100 by changing brass. The difference between 100 degree day and 70 degrees can be 100 FPS, and you can loose another 100 between 70 and freezing.

So add it all up, and just by changing brass, primers, and shooting on a different day you can very 400 fps.

Throw in barrel length, chamber size and freebore, and well, you get the point.

As a beginning chronographer it's best to have as few expectations as possible. Use it alot, and begin creating your own data set. Shoot the same load in different rifles. Test the same load in the same rifle at different temperatures... After a few thousand rounds over the chrony you will begin to get a feel for "reality".

As for published velocities, I don't believe them until I've verified them with my chrony, in my rifle.

 

[FOTIS]

Nosler speeds are off.

When has the last time someone used 67 gr RL22 to launch a 140 BT at 3350 from a 7mm rem mag?

 

[SJB358]

Nosler speeds are off.

When has the last time someone used 67 gr RL22 to launch a 140 BT at 3350 from a 7mm rem mag?

No kidding! That would be a screamer though!

 

[Oldtrader3]

Nosler speeds are off. In most large case capacity cartridges, I have to go up about 2 grains to equal their MV's.