Chrono readings and Strelock.

[RMS65]

I'm new to chronographing powder burners. I needed to set the chrono about 10-12' from the muzzle to get it to read reliably. Is that close enough I can use those velocities in Strelok?

Second unrelated question. Is it normal for velocities to climb a little bit as the ambient temps increase? Both my 6.5 and 223 went up about 25 to 40 fps as the day went on.

Thanks.
Ron

 

[Ledzep]

What kind of chronograph are you using? If this is an optical type chronograph I hate to say it but it's a better comparative tool than it is for actually measuring velocity, and I don't know that a guy can truly ever trust outputs from it without a grain of salt.

Velocity rise with temperature is usually powder dependent. Most rifle powders will increase pressure/velocity with increased temp. Often pistol powders will do the inverse. It can also be related to copper/carbon fouling, too, though. And I guess if you're using an optical chronograph it may also be related to the position and exposure of the sun, unfortunately.

 

[RMS65]

What kind of chronograph are you using? If this is an optical type chronograph I hate to say it but it's a better comparative tool than it is for actually measuring velocity, and I don't know that a guy can truly ever trust outputs from it without a grain of salt.

Velocity rise with temperature is usually powder dependent. Most rifle powders will increase pressure/velocity with increased temp. Often pistol powders will do the inverse. It can also be related to copper/carbon fouling, too, though. And I guess if you're using an optical chronograph it may also be related to the position and exposure of the sun, unfortunately.

Thanks. Yes I'm using a optical chronograph. It's a Competition Electronics. It might not be exact but it seems plausibly close given the advertised velocities and barrel lengths. I'm just wondering if there could be enough difference between the actual muzzle and 10-12' feet away to make a difference in Strelok. Is it 10 fps or is it 100 fps? I have no idea. I imagine there'd be minimal velocity loss in such a short distance. I just don't know.

 

[SoftCookie]

I use a similar chrono just to get my base numbers for Strelok then I go off the velocity that Strelok uses after truing. But again, this is also for 22lr.

 

[RMS65]

I use a similar chrono just to get my base numbers for Strelok then I go off the velocity that Strelok uses after truing. But again, this is also for 22lr.

What's "after truing".
Thanks

 

[MDof2]

After truing your ballistic solver / calculator. Kestrel, Strelok, Shooter, AB, Hornady DOF, etc.

It's highly unlikely that any variable in velocity from MV at 6" to 10' or 12' away from the muzzle will affect your solution, or data.
To check, enter what you are getting for velocity at 10' away, say 3000fps, then figure out what you hold is at 600 yards.
Now change your MV to 3002fps and see what the solution is for 600 yards.
Probably not a number you can shoot.

Whatever that MV number is, while precisely accurate or not, is often adjusted when truing your calculator at distance.
There are several videos on youtube on truing a kestrel or other calculators. Probably a good place to start to get your head around the topic.

I'd also consider a chronograph that is more user friendly than the CE.
Magnetospeed or the Garmin Xero are excellent options and will serve you well. Easy to set up, transport, doesn't require going downrange to adjust, etc.

In regard to your other point, yes, some powders are quite temp sensitive.
Several published temp / power charts available to reference as well in your testing.

 

[6.5SH]

Thanks. Yes I'm using a optical chronograph. It's a Competition Electronics. It might not be exact but it seems plausibly close given the advertised velocities and barrel lengths. I'm just wondering if there could be enough difference between the actual muzzle and 10-12' feet away to make a difference in Strelok. Is it 10 fps or is it 100 fps? I have no idea. I imagine there'd be minimal velocity loss in such a short distance. I just don't know.

From the Oehler M35 manual:

MUZZLE VELOCITIES FROM INSTRUMENTAL VELOCITIES
The velocity recorded by the chronograph corresponds to the velocity at the
midpoint of the screens. This velocity is lower than true muzzle velocity by
the amount of velocity lost between the muzzle and the midpoint of the
screens. Typically the midpoint is 12 feet or 4 yards from the muzzle.
Look in the tables provided by the ammo or bullet manufacturer to find the
velocity lost in the first 100 yards at your approximate velocity level.
Divide the 100 yard velocity loss by 25 to find the loss in 4 yards. Add the
4-yard loss to your chronograph reading to get muzzle velocity.

 

[SoftCookie]

What's "after truing".
Thanks

See reply above regarding truing. But I'll give you an example of the chrono data I have and what I use in Strelok.

Pro Chrono DLX set at 10' away I was getting an average of 1043fps
Garmin Xero set a few inches back from the muzzle, my average was 1107fps

I initially set my Strelok to use 1043fps and zeroed in at 50yds
I shot out to 100 yards using what Strelok suggested but I was way off the point of aim

For instance, Strelok says hold over 2mils for 100yards, but in reality, 1.7mils gets me in target. So by truing, I adjust Strelok by telling it that 1.7mils for 100yards was the correct adjustment. Strelok will then adjust my velocity to 1128fps.

Hope that helps explain it.

 

[carbonbased]

For instance, Strelok says hold over 2mils for 100yards, but in reality, 1.7mils gets me in target. So by truing, I adjust Strelok by telling it that 1.7mils for 100yards was the correct adjustment. Strelok will then adjust my velocity to 1128fps.

By “telling Strelok” do you mean that you enter a higher muzzle velocity or by changing the zero offset? Or maybe you mean changing something else.

Anyway, you change some parameter until the Strelok info lines up with the real world.

In other Strelok news, I believe I need to input weather adjusted muzzle velocity fps that I got from my Garmin over the winter (below). I think Strelok just automatically adjusts its output based on what temp you enter on the main screen.

 

[carbonbased]

Oh crap, perhaps you mean the truing section!

 

[smoothy8500]

Considering that certain errors affect imputs/outputs such as potential scope error (1-3% if it's a Leupold Mk4 ) or optomistic B.C. values (Hornady melting tips?), I just accept whatever the chrono "says" and true the Strelok with my dope at 600.

 

[SoftCookie]

Oh crap, perhaps you mean the truing section!

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That's it.