Ladder Test, Muzzle Velocity, and Chamber Pressure

[steelbanger]

When performing a ladder test we are looking for rounds loaded with different powder charge weights to impact the target at similar heights. If we can assume that muzzle velocity has a larger effect on the height of impact than barrel vibrations it infers that we are getting similar muzzle velocities over a range of powder charge weights. If we plotted muzzle velocity vs powder charge weight the curve will have flattened out over that range of charges.

Does anyone have strain gauge data on chamber pressure that can give us insight into what is happening to the pressure curve over this range of charge weights correlated with muzzle velocities? Is the assumption that the muzzle velocity is similar across that charge range wrong? Are the barrel dynamics compensating for the variations in muzzle velocity?

No strain gauge? How about measured muzzle velocity to confirm or deny that the muzzle velocity does not change as much over the range of powder weights that are in the sweet spot?

 

[fgregorio]

I do ladder tests on a routine basis using 0.1gr steps over a 2gr span. A barrel has some 4 different harmonics and movement patterns. Maybe the sweet spot range comes when all those patterns cancel each other out for a span of energy levels coming from a range of loads.
First, find the perfect load from the ladder test using a jump at or below 15 thou.
Pattern 1- vertical barrel flex. Causing the muzzle to whip vertically. The sweet spot is when the projectile leaves the barrel when the muzzle is either at the most upward point or the lowest point. You can mitigate this effect by putting on a barrel tuner that sits in front of the muzzle. Hold the rifle from the buttplate and tap the barrel with your finger listening to a spot where the tapping makes a dull noise say 4 inches from the muzzle. Screw the weight away from the muzzle until the dull noise spot is at the muzzle.
Pattern 2- barrel whip. After finding the right sweet load, turn the weight of the tuner in 1/16 of a turn increments firing 3 shot groups, until you find the tiniest group.
Pattern 3- barrel stretching. I don't know how to deal with this one.
Pattern 4- donut shaped traveling wave. It goes at 20000fps and travels between the chamber to the muzzle and back non stop.when it hits the muzzle it actually opens the muzzle. Every time it hits the bullet it leaks gas between the projectile and the wall of the barrel. The base of the obt load theory is the mitigation of this effect.
If you tap the barrel again like you did at the pattern 1 procedure, look to find the spot where the tapping noise is the loudest and stick a layer of vibration damping polymer or a deresonator in that spot.

 

[fgregorio]

Check the long family website and read their obt article. You will find the exact answers to your initial question there.
This is the link:
http://www.the-long-family.com/OBT_paper.htm