Velocity data

[ruger_steve]

Ok, so up until now I have only shot back to 300 yards but this weekend I plan on moving back to 600 where they have new electronic targets as I'm going on my own.

I am trying to work out now how much extra I will have to put on the scope so I'm not randomly shooting about on Sunday and similarly what loads to load my ammo. I have some Lapua Scenar 155 and 167gn ready to go but wondered if I'd need heavier? I am shooing from a Ruger Precision Gen 1 with Wildcat Mod and Busnell Elite 2.5-16x.

My other question is regarding velocity graphs. Looking at my reloading data I have the starting weight and the velocity that would produce, and then the maximum load and the matching velocity for that. Is all of the data between linear and if plotted on a graph, in a straight line?

Eg. (according to Vihtavuori app)
40.7gn = 2418 fps
45.8 = 2717 fps

So could I plot those at two ends of a graph and reliably use the data in between?

Thanks,
Steve

[WelshShooter]

If you're talking about using the published min/max load velocities and to extrapolate expected velocity for your powder load, that wouldn't be best practice. Actual velocity can differ a fair bit from published loads based on some variables, most importantly barrel length. While doing load development for my 6.5x47 Lapua I noticed that there were some drop offs in mean velocity compared to a linear regression, ie increasing powder charge in equal steps does not always equate to an equal increase in velocity.

You'll get much more success from measuring the velocity of your own ammunition under similar environmental conditions to when you will be shooting. Some ballistic software even allow you to record environment conditions for your 100m zero and then enter the actual conditions on any given day. This generates bullet drop at given distances for those conditions.

In fact, the Lapua ballistic software on mobile does this pretty well (I've used it to 1000 yards and it was fairly close!). As you're using Lapua bullets and Viht powder, sounds like a perfect combination for this app!

[ruger_steve]

I have knocked this up to kind of show what I mean.

Does this look right? The values in between the first and last literally just follow that line. Or is that line likely to curve?

[ruger_steve]

If you're talking about using the published min/max load velocities and to extrapolate expected velocity for your powder load, that wouldn't be best practice. Actual velocity can differ a fair bit from published loads based on some variables, most importantly barrel length. While doing load development for my 6.5x47 Lapua I noticed that there were some drop offs in mean velocity compared to a linear regression, ie increasing powder charge in equal steps does not always equate to an equal increase in velocity.

You'll get much more success from measuring the velocity of your own ammunition under similar environmental conditions to when you will be shooting. Some ballistic software even allow you to record environment conditions for your 100m zero and then enter the actual conditions on any given day. This generates bullet drop at given distances for those conditions.

In fact, the Lapua ballistic software on mobile does this pretty well (I've used it to 1000 yards and it was fairly close!). As you're using Lapua bullets and Viht powder, sounds like a perfect combination for this app!

Thanks for this. think you posted it while i was writing my update.

The main reason why I am doing this is I am petrified that I am going to go back to 600 yards on Sunday and the round is going to disappear someone and anywhere.

[mag41uk]

If you already have settings for 300 going to 600 is straight forward.
An extra 10MOA will get you on target

[1066]

Just guessing at your figures - if you were zeroed at 300 yds you will need to come up around 10 minutes for 600yds (2700, 155gn, BC .5) but as Welsh say, the figures in the book could be way out, you need to find out what your loads are doing - also I would stick to one bullet until you get some reliable figures. Bisley are now quite hot on any misses. What about a session on the zero range before you start. The official zero targets are calibrated for 155gn bullets at 2,700 I believe and will certainly get you on the target right from the start.

[1066]

:) :) Sorry slow typing there, you beat me to it.

[JSC]

Add 10 MOA to your 300yd elevation and you'll be on the target somewhere at 600.

If you still have doubts and can keep your eye to the rifle scope when you shoot, fire into the sand and that will give you a good indication whether your initial elevation is close enough.

No graph of MV vs. charge weight is going to be completely linear as Welsh says. And don't forget temperature changes will have an effect on your velocities as well.

(Oh look, I was beaten to it by two people!)

[WelshShooter]

This is a terrible picture but illustrates my point, see picture below of my load development performed for 69gr Scenar in 223 using RS40 powder I believe.

The primary Y axis on the left shows mean velocity over 5 rounds and the x axis shows powder charge. I applied a 6 degree polynomial as a line of best fit (blue) against mean velocity. I also plotted extreme spread of velocity per charge as shown on the secondary y axis on the right with another 6 degree polynomial as a line of best fit (red).

You can see that charges 21.9gr and 22.8gr do not produce a linear response should that have been assumed. Although its not a dramatic difference (20fps or so) this error would stack up if making this assumption based on published load data.

[ruger_steve]

Thank you all for the info. 10MOA up it'll be. And a great idea about shooting into the sand first.

I crapped myself the other week, shot of about 10 rounds and had absolutely no idea where they went because they weren't showing up anywhere on the target, but I KNEW the gun wasn't out since my last shoot. So I packed up to take it to the zero range to be told by an RSO 'Oh is that target still not working? I thought I had fixed it'. About £15 and 15 minutes of my time later.. thanks. Moved to the target next door and spot on.