308 Win 175gr TMK ladder test (300yds)

[Metal god]

Hey guys , I need help understanding this target .

I had been discussing a previous ladder test I did using the same components in another members thread .

Savage FCP-K 24" barrel
308 Win
Sierra 175gr TMK
AR-Comp powder
Lapua cases ( virgin )
Fed match primers

I thought I'd start my own so as not to completely hijack the other thread

So here's the target

I have the scale and velocities highlighted

The issue I had last time I ran the test was that the wind was blowing pretty strong . I had to hold for the wind which I was told screwed up my results . I also did not use a chrono . This time I there was very little wind and my hold was on each dot . As you can see half way through I went out and made the dots bigger . I was having a hard time holding on the small ones because my cross hairs completely covered them .

Each shot was fired from a cold bore at ambient temperature . At the time that was between 69 and 71 degrees through out the ladder test with the first couple shots at 69* and the last couple at 71*

The last 4 shots/charges had a slightly stiffer bolt lift . Although they had a bit more resistances I would not call them sticky and there was no extra effort needed at the lop .

Cases of the last 4 charges

What do we see here and what does it all mean ? Note: 41gr velocity dropped and did not follow the trend . I'll do a water volume test of these cases and see if that 41gr case has any differences .

I see two possible nodes
40gr (in between 39.8 and 40.2) because of the velocities stabilizing
42gr (in between 41.8 and 42.2) because of the POI

What say you ???

FWIW here is the target of the first ladder test As you can see the charges are not the same . Two reasons for that .
1) I never reached max charge/pressure the first time.
2) Since I knew I was safe at the lower charges I started and ended with higher charges in order to reach the max pressure .

 

[Jimro]

You'll get better data firing 3 shots per charge weight, but I think you have enough for a SWAG.

Your 41.8, 42.2, and 42.6 shots show minimal vertical dispersion.

Your 39.4, 39.9 and 40.2 shots also show minimal vertical dispersion.

The primers for the last four charges look fine to me as of today at these temperatures, but that may change quite a bit come August.

I recommend you load up five shots each at 39.6, 39.9, and 40.1 gr, as well as 41.9, 42.2, and 42.5 grains.

Shoot them to see if they all group inside the same group, and if so, congrats, you have two good loads for your components. If not, share your data and we'll try to help.

Jimro

 

[Metal god]

3 shots per charge in a row or round robin . If round robin then I'd be doing a OCW test correct ?

Jimro : can you explain your charge suggestions . I know where your coming from but don't understand why your only dropping .1gr . I do these ladder test in .4gr increments so when I find a stable zone I can split it in half leaving a .2gr high and low in order to give me a OCW-ish cushion .

I don't see how .1gr is going to show much difference . How I hold the rifle to my shoulder will cause a bigger velocity ES then .1gr will . FWIW I've tested this and found it to be accurate .

I'm not challenging your suggestions , only trying to understand them better while explaining where I'm coming from .

Thanks MG

Side note to all , I was looking at the last three shots and the vertical sting is very small but there velocities rise consistently . What is better to be looking for , vertical sting like the last 3 shots or a consistent velocity like the difference between 39.8 & 40.2 ?

 

[JeepHammer]

I have to go with Jimro,
I've never been able to get accurate data with single shots.
At least 3 shot groups timing cool down between rounds (not guessing).

Keep in mind that point of aim/point of impact can be corrected,
It's group consistency you are looking for.
No 'Groups', no way to tell charge consistency.

I also have to go with MG, 2/10 grain increments.
I might try 1/10 grain on bench rifles, but no powder thrower is accurate to 1/10 grain, so every charge will have to be hand weighed.

I'm also big on sandbagging the rifle, dead rest on bags/rest, no 'Nugging' the rifle into place, this allows 'Human Error' to enter the test in a big way!

A 'Test Fixture' would be ideal, but not practical... taking all 'Human Error' out of the situation.
Trust me, way more work than its worth if you only work up a couple loads a year to the Nth degree and you have good bags & steady hand!

 

[Metal god]

If you take 3 shots each letting barrel cool . It's not a ladder test . It's Dan Newberry's OCW http://optimalchargeweight.embarqspace.com/#/ocw-instructions/4529817134
and there would be no need to do it at distance . 100yds would work but I've done it at 200yds before . It worked well and I was able to produce a good load . My issue with it was that it took me 60+ total rounds for the final result . The straight up ladder test should reduce that by 20rds I'd think . I'm 10 rounds in now , lets say I try my two choices of 40gr and 42gr and load ten each . Now I'm at 30rds and now should be able to eliminate one of those charges . If the one I choose grouped great then I'm done if not then I can try adjusting seating depth at 10rds each but could likely do it in 5rd increments . I should be able to find a load in under 60rds .

My last ladder test that produced a good load took 35rds but to be honest here I've only been able to use the ladder test once that worked to produce a good load . This one I'm doing now is my 5th try including the other that used the same components . Only one has worked and is why I'm here asking the questions .

Do you guys not feel the ladder test method has any use or merit ?