OCW method - second rifle test

@414gates @414gates 3 years ago

Because I was able to achieve what I consider to be a good result with my first OCW test, I tried the same test on a second target rifle.

This is a 375 RUM, using 300 grain Peregrine Rangemasters, with N570 and Federal 215 Match primers.

Again, I have a full two percent spread where the group centers are almost identical. 102, 103 and 104 grains. The left-most shot on the 102 is indicative of a pulled shot - Dan Newberry says if the flyer is not in the direction of the previous or next charge weight group center, it's a shooter induced error.

I will re-shoot this at 102.5, 103 and 103.5 to verify that the group centers remain the same. If that works out, I can work on the seating depth.

It's been very interesting for me to see the OCW test in action, and get what seems to me to be a conclusive result.

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@J @janfred

No.

Chris Long specifically developed the OBT theory as it relates to the annular wave cased by the powder explosion. The aim is to get the velocity SD down to a minimum by predicting when the annular wave is clear of the muzzle.

This is distinctly different from the Optimal Charge Weight theory that deals with the harmonic length of the barrel and how it whips around its axis.

@O @oafpatroll

Thanks [member=860]Againstthegrains[/member], that's helpful. I got the wave form thing but hadn't clocked to the 'momentarily stationary at peak and trough' bit.

@T @treeman

Thanks [member=860]Againstthegrains[/member], that's helpful. I got the wave form thing but hadn't clocked to the 'momentarily stationary at peak and trough' bit.

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Ya, i only caught on to that recently as well, like a piston in a motor - makes sense.

@A @againstthegrains

No.

Chris Long specifically developed the OBT theory as it relates to the annular wave cased by the powder explosion. The aim is to get the velocity SD down to a minimum by predicting when the annular wave is clear of the muzzle.

This is distinctly different from the Optimal Charge Weight theory that deals with the harmonic length of the barrel and how it whips around its axis.

I completely agree with you. The swing analogy was more for illustrative purposes and understanding. It is much easier for us mortals to imagine a swing with a stationary phase, than a metal bar with a wave like pulse travelling through it.

@T @tripodmvr

My understanding is that OBT does not reflect the movement of the muzzle, but it calculates when the pressure wave is at or near the knox of the rifle. The pressure wave distorts the shape of the crown so as to form an ellipsoid shape. The node calc is then when the crown shape is least deformed and the wave at the knox. That is also why the node can be as wide as 1gr in width - the wave moving away, reflecting and moving forward again creates this.