Applied Ballistics Pro Support Thread

[hogpatrol]

This may help:

Pressure Definitions

 

[JPeelen]

Thanks for the 2nd clarification. I now understand where I was confused. I had read the AB and Kestrel Documentation before creating this post...however the way diff in Barometric and Station pressure was described led me to believe that the airport reported Pressure should always come close to Station pressure (though not 100% matching). I dont know if AB guys are reading this...but I would suggest that in the concerned portion of the guide (attched), they add one example, something like this: Raton Airport located at ~4k Feet elevation will have Station Pressure of 24" but its reported Barometric Pressure will be ~30.2".

Adding an example with some numbers might help less smart users like me.

Modern instrumentation allows us to measure the local temperature, air pressure and relative humidity at the firing point(!!!). From this, modern electronic devices can easily compute what is needed for the ballistic solution: air density and speed of sound.
If we used this straightforward approach, we would not need to think about the numerous definitions of "air pressure" that are so thoroughly confusing the shooters. Be assured that even professional military ballisticians (I could quote two publications.) sometimes get lost in this respect.
Altitude density in particular is a tool from the time before electronic devices were available. It is a rather crude method based on simplifying assumptions. But it was all that could be handled at the time.
Todays computing power enables us to use less confusing methods.

 

[sjoliat]

Has the abmediaresources.com page been hacked? I tried to pull it up and was redirected to a spam site.

 

[T.Rhodes]

I’m going through Litz’s “Applied Ballistics For Long-Range Shooting “ and have a question about the velocity equation 5.3 in appendix B.

Can this be used to establish a new velocity for different bullet even if a new barrel was installed ( 24” to 30”) and a twist change from 8 to 7 1/2? In my case, for 6.5cm going from 140grain ELD-M to Berger 153.5 LR Hybrid.

I would appreciate input/thoughts on if this, is it valid or too many changes to be of use finding what a good velocity should be.

Tia

 

[JPeelen]

As Bryan Litz in his book (p. 69) writes regarding this equation: "The assumption is that the kinetic energy at the muzzle [of a given barrel] is constant."
You are going to change to a longer barrel. So you first need to measure your 140 gr bullets from the new barrel. Then you can apply the equation to estimate the velocity of 153.5 gr bullets, provided the load works "at the same pressure", as Bryan Litz writes on p. 68.
As said above, the equation is only an approximation that is based on the assumption that old and new bullet will have about the same muzzle energy from the same barrel.

In other words, the equation has no element to express barrel length. So it cannot consider the effect of barrel length change. In my opinion the effect of twist is negligible.

 

[T.Rhodes]

Good point. I should have done that - measured 140 ELD-M's out of new barrel. I don't have any more of the Hornady's, but do have some Berger 140's. So as far as just getting velocity on a 140gr mass out of the new barrel, it may be in the ball park...maybe? If that is close, then the equation may give a velocity to load to. I expect to see an increase in velocity going from 24" to 30" barrel length.

Thank you for your input.