Load test By Velocity Nodes - part 1

H

hounddawg

New member
Decided to kill 2 birds with one stone yesterday. I have been curious about this since I read it

http://www.65guys.com/10-round-load-development-ladder-test/


I was going to do the experiment using my .223 bolt gun but decided to try it on my recently built .260 tactical. The gun has a Savage 10 action, 24 inch Criterion barrel with a Precision Armament muzzle break set in a MDT LSS aluminum chassis. The barrel had 45 rounds through it for break in. break in rounds were a mixture 25 rounds of IMR 4350 and 20 rounds of 4831 SC using Nosler 140 CC's.

I have 500 123.3 SMK's on the shelf and decided to do a load workup using Varget

Velocity results were flat and all groups were mostly MOA but unimpressive. Bullets were seated .030 from lands

Name: 260 123 Smk Test

Notes: 38.9 grains varget
Shots: 3
Average: 2756 FPS

Notes: 38.7 grains varget
Shots: 3
Average: 2743 FPS

Notes: 38.5 grains varget
Shots: 3
Average: 2737 FPS

Notes: 38.3 grains varget
Shots: 3
Average: 2713 FPS

Notes: 38.1 grains varget
Shots: 3
Average: 2722 FPS

Notes: 37.9 grains varget
Shots: 3
Average: 2771 FPS

Notes: 37.7 grains varget
Shots: 3
Average: 2713 FPS

Notes: 37.5 grains varget
Shots: 3
Average: 2699 FPS

Notes: 37.3 grains varget
Shots: 3
Average: 2677 FPS

a couple of things that jumped out at me was that were that in one case a lower charge actually had a higher average which was probably due to a chrono error. However the velocity was between 150 - 200 FPS from the same bullet shot in my 26 inch barreled gun. The plus side is thqat the velocity had a very flat slope.

To illustrate the velocity difference between the 26 and 24 inch barrels here are some numbers from the break in using 140 Noslers over the same load of SC4350

Name: 140 Nos 44.1 gr 4831 Tactical rifle

Shots: 10
Average: 2547 FPS
SD: 25 FPS
Min: 2506 FPS
Max: 2578 FPS
Spread: 72 FPS
Barometric Pressure: 30
Temperature: 63


and from a test I ran last December using my competition rifle with a 26 inch barrel using the same load

--------------------------
Name: 140 Nosler 4831SC
Notes: 44.1gr

Shots: 5
Average: 2731 FPS
SD: 8 FPS
Min: 2721 FPS
Max: 2743 FPS
Spread: 22 FPS
Barometric Pressure: 30
Temperature: 50


Notice the velocity decrease from the 24 inch barrel. My first thought is I need to be using a faster powder. I have some IMR 4895 and next week will work up a load using that since I would like to get this gun up to around 2850 or 2900 FPS minimum using the 123.3 's.

I will be starting all over on my loads however since I have decided it is time to retire my Lapua brass due to the primer pockets are getting sloppy. I ordered 250 Peterson with small rifle primers last evening

thoughts ?
 
Last edited:
Several.

First, the 10 shot is supposed to be 10 shots, not 30. :) Without seeing the ES on the 37.9 load, not sure if you had one squirly load or not.

Second, almost every barrel I have shot over the chrono consistently had sped up in the first 100 to 200 rounds, so a 10 shot ladder test in those first 200 is maybe not a good idea. I have seen as much as 70 fps difference in the same barrel after a few hundred rounds and speed ups as much as 80 fps in the first few hundred rounds.

Third, if you graph out your data, looks like you still found a node or two.

When I run the 10 shot ladder test, I go by 0.1 grain increments around the charge weight I "think" I want to use. The procedure is valid, but consistency is king. I go slow and I shoot 2 rounds before I start the test to get a little heat in the barrel. Then I shoot 1 round every 3 minutes and put a puff of compressed air down the bore after each shot.

I load 2 rounds of each charge weight just in case I happen to have an issue. The last time, I did the ladder test twice (yes, just over an hour to shoot 20 rounds) to kind of check myself and both tests showed the same two nodes.
 
thanks for the reply but I used 3 shot groups instead of single shots in order to get a better idea of average velocity. Also I have never shot 200 rounds in one sitting across my chrono in one session nor do I ever plan on doing so, but thanks anyway. On the barrel temperature I use a Fluke meter setup with the thermocouple taped just in front of the barrel nut to monitor barrel temps. A 3 minute cool down in 40 degree weather is going to affect barrel temps more when the temps are in the mid 90's. That is just common physics. It is better to use a thermometer and do a cool down when the temps get 10 - 15 degrees F above ambient

What I am really more interested in is the velocity drop. I expected to see some drop but have a feeling the powders I have been using are not getting completely burned before the bullet exits the barrel
 
Last edited:
part 1.2

looked at the velocity data and plugged it into a ballistics calculator and came up with a muzzle velocity 2700 FPS @800 it would still be traveling at almost 1500 FPS so anything after that is gravy. BTW dropped some on the scale and this is the newer 123 SMK not the older 123.3 it has a BC of .510 .

here is the target with the OnTarget analysis

https://imgur.com/a/fSFH1

There was only 13 FPS difference between 37.7 and 37.9 grains averages

the key point for me on this target is the CEP numbers and the low SD on the Y axis (vertical)

Next weeks plan is loading up 15 rounds at 38.7. Five will be @.005 from lands, five @ .25 and the last five will be .050 from lands. I will the do the same with 38.8 and 38.9. If the velocities, the CEP's and the vertical spreads remain good the I will have my load for this round at 38.8 which will flexible with the charge weight

The step after that will be loading up some bullets with IMR 4350 and see if at the same muzzle velocity that bullet shoots the same
 
Also I have never shot 200 rounds in one sitting across my chrono in one session nor do I ever plan on doing so, but thanks anyway.
Click to expand...

I never have from one bolt gun either. Maybe 50 max. But what I referred to is multiple sessions with a new barrel to be able to tell when it has stabilized. Just my opinion having shot a lot over chronos with new barrels, that most speed up and there are some peaks and valleys that are anomalous.
 
I was discussing this earlier with a friend and he told me he first started using the velocity node method back in 2014. My friend is a regular winner in F Open so I guess there is something to it. Mark Cortina who is a world class shooter was blogging and posting about his variation on it back in 2013

http://forum.accurateshooter.com/threads/long-range-load-development-at-100-yards.3814361/

My bad I thought you were referring to 200 across the chrono not down the tube.
 
Last edited:
Why did you choose .025" increments? And is it just bergers that jump miles for accuracy?
Click to expand...

I have experience with this bullet in a similar gun which gets .3 groups jumping the same bullet .025 from lands. It is not that great a long range bullet in that gun but it will shoot the lights out to about 300.

However this is a different barrel and different throats so I will try one setting closer in and another farther out hoping that the closer bullet will shoot better or at least the same as the .025 and the .50. The closer you can seat in safely the less chasing the throat you have to do if it is a jump tolerant bullet

edit- the only Berger's I have shot are the 155.5 30 cals and they liked it real up close and personal in my gun. I mostly shoot Nosler CC's and Sierras. If I ever get to where my wind calling outruns my bullets accuracy then I might start shooting the high ticket bullets :)
 
Last edited:
You must log in or register to reply here.
Back
Top