I eFed up a load development ladder test

[MarikinaMan]

Like it says, I eFed up a load development ladder test.

I loaded up Nosler 69gr HPBTs with Accurate 2520. From 223 all the way to 5.56 loads.

Here’s the results:
22.2gr - 2510 FPS
22.4 - 2500
22.6 - 2408
22.8 - 2346
23- 2569
23.2 -2434
23.4 - 2448
23.6 - 2559
23.8 - 2447
24 - 2454
24.2 - 2480
24.4 - 2618
24.6 - 2566
24.8 - 2589
25 - 2648
25.2 - 2759
25.4 - 2746
25.6 - 2769

I don’t get it. The velocity goes up and down. I’m not sure what’s going on. Either my chrono is toast, or someone went into my loading room and dropped my Ammo box and put the Ammo back randomly or the 20 degree temp drop in the desert today screwed me over. So frustrated. I loaded these in November and today was the only day I had a chance to clock em.

[MarikinaMan]

The Hornady 75gr HPBT ladder faired better but was still kinda off.

22.2 2398
22.5 2448
22.8 2395
23.1 2438
23.4 2533
23.7 2546
24 2559
24.3 2545
24.5 2667
24.7 2657
25. 2707
25.3. 2756
25.6 2785
25.9. 2812*
26.1 2848*

*Flattened primer

[ar15barrels]

Velocity changes with ammo/barrel temperature.
So if you shoot a string of the same charge weight, the velocity climbs as the string progresses.
You need to be very consistent in your shot-to-shot times when you are comparing different charge weights, or the actual shooting will effect the velocities.

You also need to control for how long a cartridge is in the chamber.
If your barrel is warm, letting the cartridge sit in the chamber warms the ammo up.
You should control for how long the cartridge sits in the barrel for every shot to eliminate that variable.
This is easy in a bolt gun, you simply chamber the cartridge and close the bolt a couple seconds before you are ready to fire.

You also need to control for ammo temperature.
Ammo left in the sun is warmer than ammo kept in the shade.
Ammo left out of the box in cold weather is colder than ammo kept in the ammo box until right before you load/shoot.

[MarikinaMan]

Im looking for flat spots in the velocity, but this data has scratching my head.

[MarikinaMan]

Thanks Randall.

I was loading mags one at a time to manage the test. I was shooting within 3 seconds from dropping the bolt.

[ar15barrels]

Im looking for flat spots in the velocity, but this data has scratching my head.

What do you expect is going to cause a flat spot in the velocity?
I doubt that most consumer chronographs are accurate enough to see such small changes in velocity as the small patterns are smaller than the intrinsic measurement error.
Most consumer chronographs are like +/-1% accuracy.

On a 2500fps shot, that is +/- 25fps on any given single shot.

[MarikinaMan]

What do you expect is going to cause a flat spot in the velocity?
I doubt that most consumer chronographs are accurate enough to see such small changes in velocity as the small patterns are smaller than the intrinsic measurement error.
Most consumer chronographs are like 1% accuracy.

On a 2500fps shot, that is +/- 25fps on any given single shot.

I was trying out this process http://www.65guys.com/10-round-load-...t-ladder-test/

[ar15barrels]

I was trying out this process http://www.65guys.com/10-round-load-...t-ladder-test/

Flat spots being a series of charges that are closer in velocity than the rest of the test.

You can't simulate a ladder test with a chronograph.
The ladder test works because it is showing you a visual representation of where in it's vibration node that the bullet releases from the barrel.
As you approach the end (top or bottom) of a node, the bullets will group together.
The velocities of those 3 bullets that group together will NOT be similar though.
The slowest bullet will still have been heading towards the node and the fastest bullet will have been past the node and headed the other way.
The one in the middle will be the one ON the node.

Trying to use a chronograph to find a vibration node in a barrel is like using a flashlight to smell a gas leak.

[MarikinaMan]

You can't simulate a ladder test with a chronograph.
The ladder test works because it is showing you a visual representation of where in it's vibration node that the bullet releases from the barrel.
As you approach the end (top or bottom) of a node, the bullets will group together.
The velocities of those 3 bullets that group together will NOT be similar though.
The slowest bullet will still have been heading towards the node and the fastest bullet will have been past the node and headed the other way.
The one in the middle will be the one ON the node.

Trying to use a chronograph to find a vibration node in a barrel is like using a flashlight to smell a gas leak.

I’m testing the system just to see for myself. I have a load from a traditional ladder test that I will compare it too.

I get what you’re saying. I find this method to have merits logically and quite intriguing. My hope is that I will find a load using this process, and compare it to my usual. I’m not gonna say it works, coz I haven’t even developed a load yet.

Not gonna happen with this effed up testing

[MarikinaMan]

Here is vid if you ever wanna look at it https://youtu.be/RgGrRlB38CI

[JackEllis]

I just looked back over my .223 test data. I generally step up charges in .3 or .5 grain increments. None of the 6 or 7 tests with varying charge weights show velocity falling off as charge weight increases. The slope of the velocity vs. charge weight graph may flatten a bit, but it never goes negative.

[MarikinaMan]

Interesting result when I finally graphed the data.

The 69gr test, as jumpy the data is, shows a flat spot at exactly at 24, my usual load from a traditional ladder test. There is also a flat spot at 25.4.



The 75 grain test came up with a different result, but close. 23.7 vs my usual load of 24.2.



I'm going to load up 10 each for the 75 gr and do some 200 yard groupings later this year.

[kcstott]

You can't simulate a ladder test with a chronograph.
The ladder test works because it is showing you a visual representation of where in it's vibration node that the bullet releases from the barrel.
As you approach the end (top or bottom) of a node, the bullets will group together.
The velocities of those 3 bullets that group together will NOT be similar though.
The slowest bullet will still have been heading towards the node and the fastest bullet will have been past the node and headed the other way.
The one in the middle will be the one ON the node.

Trying to use a chronograph to find a vibration node in a barrel is like using a flashlight to smell a gas leak.

The methodology is not looking for a vibration node but a pressure node. and the system works. It can be followed up with a traditional ladder from the pressure node you found but in reality why when you can shoot 30 rounds and get a one hole group worked up. It was not meant to replace a traditional ladder test, but to get good load data quick. I don't have the time nor do I care to waste my barrel life doing 100 round ladders

[nn21]

Here is vid if you ever wanna look at it https://youtu.be/RgGrRlB38CI

https://www.youtube.com/watch?v=9s9JymZntlk Gavin just did one, too. He steps it up at the end and does a 5 shot of each of his 10 charge weights.

[MarikinaMan]

https://www.youtube.com/watch?v=9s9JymZntlk Gavin just did one, too. He steps it up at the end and does a 5 shot of each of his 10 charge weights.

Nice. I hadnt visited this subject since last year. I actually shot loads that have been in a box for months. I'm watching the vid right now.