Load development with a chrono

[Seddo]

Hi guys,

For the first time i'm trying the idea of mapping velocity to see if you can really find a good load without putting any shots on target. When i got my 6mmBR i had a similar attepmt nd it turned out well, i took 15 rounds to the range, 3 rounds of 5 different loads. I fired one of each and cleaned between each shot for the first 5 rounds (my run in process) and then fired 2 of each load over the chrono (10 rounds). I got a pair of shots with a single figure ES so when i got home i loaded up 30 of them and shot a 600y f class match the next days and had almost no vertical. The lack of vertical got me interested so when i had 5" of barrel removed from my 6.5 Creedmoor i decided it was a good time to start plotting.

What i did this time was fire 9 different loads over the chrono for the 2 bullet weights i had in mind and plotted the results. I fired a shot and then reset the chrono as there has been some discussion as to the accuracy of the first shot over a magneto speed chrono. After the 7 shots i let the rifle cool before repeating the process for all the rounds. I got a bit impatient for the last strings and didn't let it cool as much as the previous strings.





As you can see from both charts there are flat spots in the velocity at various points in the charge range so this is where the loads should be more forgiving on target.

From the above data i picked the following loads to shoot groups with:
140gr - 41.4gr & 42.3gr  
123gr - 43.8gr & 44.7gr

In the next few weeks i will shoot the groups between 200-300y and see what happens. If everything goes to plan i should have a good load for each bullet weight and then it will be a matter of fine tuning it with OAL changes's if i get around to it.

Has anyone else tried this method of load development before?

[stinkitup]

Interesting read and like your graph skills [WHITE SMILING FACE].

Have read a few guys methods over on 6br and some use similar...i think that 123gr in the 44.5 or .6 would give some lee way either side by the looks. 140 looks tougher to.pick but there are def 2 flat averages there to try.

[LoneRider]

i wouldnt rule out 45.3 or 45.6 with the 123gn either....
or 42.6 with the 140gn.....just for for accuracy testing....
but...what do i know,ive never used a chrony...

[Brad Y]

Yes its possible to do it (particularly if you have had similar barrels chambered with same reamer and using same components as you will know a rough area). You need to look at the lines on the graph similar to reading groups on short range testing. Note while you might find a stable charge area you will have to work on harmonics with the free flight (seating depth) to get the group shape you want.

[Camel]

This whole process and the graphs have me scratching my head for a couple of reasons,

1. I cant read graphs and don't know what they mean.
2. I am a lazy bugger and just do things the old way, of load a few weights and shoot a few groups

But then Im not much interested in the target shooting scene. Yeah, I know, Im an old fart,

[Tony Z]

As someone who has developed LR rifles for others and myself i cannot see a connection of velocity ES with accuracy based purely on the numbers alone. There are hundreds of posts regarding this topic where the vast majority have virtually come to the same conclusion. You will burn out a barrel running the numbers game with the most common question being "why is my gun shooting so poorly yet my chrono says I'm getting single digit ES?".
Identical velocity is no guarantee of accuracy where long range is concerned. The simple fact is that 3 or 5 is not a ligitimate test. 100 is and when Henry Childs ran his tests using a 100 as a sample each of different loads the ES was identical to a point in each load. Simply if the same bullet, powder etc is used the same error will eventually show up. Basically what Childs is saying is fire enough shots and the single digit or zero ES disappears very quickly. Foolish to think otherwise. He did his tests on corrected velocities on a pair of Oehler 43s.
To bring it to the base line, components produce the ES and changing components alter ES for better or worse. The fact is that some components produce a lower ES where from there it is up to the shooter to find the right node. Velocity is totally irrelevant except for range charting but can be used for future tuning of the same barrel if primer or powder lots change or even if weather changes.
For example in 2013 at the SCC my 6 BR was a full minute higher at 1K than here at home. By dropping a half a grain of Re15 and velocity back to 2930 the accuracy was back, POI was where it was supposed to be and i went on to win the LG class with a half MOA aggregate. On the other end Trevor had to increase his charge to get to 2830 fps with his 284 and went on to shoot small group and run second at the same match.

Best of luck trying the numbers game Seddo but be aware no-one has run it successfully on its own to produce an effective combination.

[als008]

Hi Seddo,

Check out this series of videos on Youtube. It looks a lot like what your talking about in your post.

https://www.youtube.com/watch?v=O4K4l0KzRfg
https://www.youtube.com/watch?v=vTFogo7n-5E

[big G]

I'm going to load some 123 AMax with 2009 now.
I like what you have presented.
Biggy.

[Seddo]

I havent had time to test them yet, the barrel is with the gunsmith getting a thread cap made and the barrel cerakoted. I figured there was no point in doing any final work until it was completely finished.

[Tackleberry]

i go the other way get a load that groups well at 1000 yards and the run 5 over

the crono with at least 10 min between shots to get a better rep of speed and

if i'm happy with the velocity thats it if not i go up to the next node .

only takes one day and all done it has worked for me for years .


cheers D