Relationship between bullets weight and barrel harmonics

[Ron AKA]

So you mean that the barrel "wave" is the same regardless of the bullet weight/type? Interesting. I was thinking that the wave of the barrel has a different amplitude if the bullet is heavier, because the peak of the pressure will be different (higher on the case of a heavier bullet).

The barrel wave, is not really a wave. It is more a waggle like a fishing rod waggles, especially when you have a weight near the end of it. When the primer fires and ignites the powder, it starts a waggle of the whole gun, but in particular the barrel. The frequency of the waggle is determined by the barrel length, weight, contour, and to a lesser degree how it is bedded in the stock. Has very little to do with the bullet weight. Varmint Al claims that in a centerfire the bullet exits before a full natural harmonic wave is set up. The initial waggle is a forced response to the powder charge and recoil.

What is of critical importance is the direction of the barrel muzzle when the bullet exits. You can control that with velocity.

You can see some graphics at Varmint Al's site.

 

[Evil_Dark]

Yeah, I know that it is not visually like a wave, but I was imagining it more like a guitar string. But my limited english have its issues when I try to explain very technical things!
Thanks for the link, I will read more on the subject.
Dark

 

[Evil_Dark]

After looking at my shooting log and hand written data, I found my mistake regarding the load test that I made.
First load test (ladder test) my seating was deeper than the rest. So the COAL was 2.820" for the load test 39.5gr @ 40.6gr, and the COAL was 2.880" when I tested the loads between 41.3gr @ 41.7gr. For the same powder charge, I got 50FPS more with a longer COAL (0.060" longer). And funny, when I tried the loads between 39.7gr @ 39.9gr there were a even bigger jump in velocity, 80FPS+ for a 0.020" longer COAL.

My rifle have a very short chamber, with the cleaning rod method (measured with the 208gr ELD bullet) the COAL of the bullet should have only 2.630" to touch the lands. Is this can explain the high jump in velocity?

Dark

 

[Ron AKA]

After looking at my shooting log and hand written data, I found my mistake regarding the load test that I made.
First load test (ladder test) my seating was deeper than the rest. So the COAL was 2.820" for the load test 39.5gr @ 40.6gr, and the COAL was 2.880" when I tested the loads between 41.3gr @ 41.7gr. For the same powder charge, I got 50FPS more with a longer COAL (0.060" longer). And funny, when I tried the loads between 39.7gr @ 39.9gr there were a even bigger jump in velocity, 80FPS+ for a 0.020" longer COAL.

My rifle have a very short chamber, with the cleaning rod method (measured with the 208gr ELD bullet) the COAL of the bullet should have only 2.630" to touch the lands. Is this can explain the high jump in velocity?

I am not following those COAL measurements. I have never heard of doing a measurement with a cleaning rod. It is better to measure from the cartridge base to bullet ogive, and compare that to a measurement of what your base to the lands measurement is.

 

[BCBRAD]

That is the "theory" being spread by those who make the computer program that makes such predictions. I don't believe it. Varmint Al is on the right track with barrel vibration, and barrel position at bullet exit.

Was out shooting this AM, 5C and winds gusting from 5-10 mph, elevation 2880 feet.

My two 6 Dashers shot 0.5 moa ,5shot groups at 200m/219 yards which is pretty typical, they are rebarrelled Tikka T3's. I am in the process of changing to Varget from H-4350.

Also, the Savage LRP in 260 Rem was employed as well, 140 Hybrids jammed 0.008". 0.6 moa at 300m/330 yards

Followed QL in all these loads, referred to OBT sheet, came up with a charge weight and a velocity.

Minor tuning on charge weight and I'm done with load development with these changes in components .

ES was near single digit all way around , which means these loads will stand up at a 1000.

In no way am I saying the traditional methods to get a good load are not valid, but with the use of QL, OBT tables, and ultimately OCW is what we are after, QL and LabRadar are game changers.

A very good shooter will shrink these groups a lot further than I can.

 

[Ron AKA]

Was out shooting this AM...

But have you done a traditional Ladder Test to verify that you really are loading to a velocity sweet spot? If you have not, then how do you know you have really optimized your load?

 

[BCBRAD]

I have serious doubts that the equipment I am using , with me driving it, will do consistently better than 0.5 moa.

I have one 'rig' that will do ~0.3moa, load was found using 'non-traditional ' methods.

(velocity sweet spot).......for example, say a velocity of 2920 ft/s which seems to be a sweet spot for a 6 dasher using Varget and a 26" bbl, if you change to a different powder then the sweet spot of 2920 ft/s goes away due to the gas generated by the burning powder has different rates of acceleration thus differing the vibration signature.

So, a new ladder test would need to be done or a few key strokes on the computer to find that ever elusive sweet spot.

Just a different way of getting a result.

 

[Ron AKA]

I think you are letting your computer software over complicated the issue. I recall I switched from H322 to Varget with no significant change in velocity sweet spot. I also use the same sweet spot for three different bullets. I do it because it works. I have no computer program to keep happy.