Thread: Trying something, Eric Cortina method of load development

Have you watched Eric's vids on 'reading groups' ?

No, best do that, no doubt will be interesting.

Reviving an old thread of mine as I'm back at it again. This time working up a load for a 30-06 ackley improved
After fire forming with some sako brass and cheap 155gn fmj, I loaded a charge ladder starting at 59gn working up to 60.5gn with 178gn eldm's seated over adi 2209.
I actually did a lower charge weight ladder starting at 57gn but I cocked up my jam measurement and it was a disaster, still the velocity of the lower charge ladder gave me confidence to start higher (without the projectile jammed hard into the lands )
Found a good consistent velocity the higher I went with charge weight, for now I will settle at 60gn which gave an ES of 9fps and a SD of 4 fps which I thought was pretty darn good.
I have since loaded a seating depth ladder to find where the velocity node intersects with accuracy as at the seating depth I used the charge for weight ladder the accuracy was less than stellar at 1.5"-2"
My seating depth ladder starts 3 thou shorter than my charge depth ladder and continues dropping 3 thou each increment for 10 loads all at the same charge weight. I'm sure I will find accuracy somewhere I my seating depth ladder if not I'll look at doing a bedding job on it, as the rifle currently sits in a b & c stock with alloy inlet chasdis but the barrel although free floated is not bedded around the taper.
So far so good, if I can get the 60gn load down to sub moa at 2940-2950ish fps with 178 eldm's it'll be an absolute slayer and I'll be stoked


Charge ladder veloicties



Seating depth ladder ready to shoot tomorrow all going well

Originally Posted by ebf

@Danny, what you describe above is what I've been doing for the last 5 years.

IT WORKS...

I use a hornady modified case & gauge to get lands measurement, but it requires some "feel" and a light touch. Helps if you repeat with several projectiles (most projectiles have pretty large variation when it comes to BTO) and average the value.

Hardest part for people to get their head around is not shooting groups during initial load dev.

Neck tension is the holy grail of accurate ammo. There are several approaches to maximize this in terms of your reloading process.

Neck tension= annealing.

Originally Posted by TeRei

Neck tension= annealing.

Yup I aneal my cases and definitely notice the neck tension feels a lot more consistent when seating

Interesting afternoon at the range shot my seating depth ladder and have nailed a pretty sweet load.
So yesterday the load that had the best ES and SD shot a less than stellar 1.8" 3 shot group, the ES was 9fps and the SD 4fps which I thought was pretty damn good and warranted further investigation even if the 1.8" 3 shot group at 100y from the charge ladder did leave me feeling a little concerned.
I put the group out of my head and set about loading a seating depth ladder 10 steps, 3 rounds loaded at each step, 3 thou difference seating depth between steps so 30thou difference from closest to jam to furthest from jam.
I went back to the range and set about getting things set up, today I decided not to run the magnetospeed on the barrel as I wanted to make 100% sure there were no external influences that could affect the harmonics, especially as the barrel is an extremely light weight profile and fluted as well.
Immediately right from the first load (which was 3 thou shorter than the charge weight ladder groups) the groups were better, they sort of fluctuated a little then at 12 thou into my seating depth ladder they tightened right up to .8" then 15 thou .5" 18 thou saw the group back out to .7" as did the next 3 groups after that slowly increasing in size again but all sub moa.
Then at 27 thou it shot a .2" clover leaf group, the last group after that was only 2 rounds as I ran out of prepped brass but it opened back out up to 1.1".
So in conclusion I will settle on the 15 thou group that was .5" and some might ask why not the .2" seating depth and my reason is the .5" group was right in the middle of a big stable node of sub moa group producing seating depths from 12thou-27thou the last group in that node was the .2" group before it opened right out to 1.1" just 3 thou deeper so my logic is that the .2" group is right on the very edge of that accuracy node where as the .5" group is closer to my jam and has good grouping over 15 thou of tolerance so is right in the middle of that accuracy node.
Whilst this may come accross as tedious and OCD it definitely works, the other issue is that the factory trigger on this rifle is a heavy bitch and will need sorting I suspect it will be easier to shoot good groups once I've had the trigger lightened.
All in all happy to have a nice accurate load sorted. I will load up 6 or 9 confirmation loads to krono for velocity validation as I didn't krono the seating depth ladder.
End result should see 178gn eldm's at a velocity in excess of 2950fps.
I'll post pics of the charge ladder and seating ladder later this evening

Originally Posted by dannyb

Interesting afternoon at the range shot my seating depth ladder and have nailed a pretty sweet load.
So yesterday the load that had the best ES and SD shot a less than stellar 1.8" 3 shot group, the ES was 9fps and the SD 4fps which I thought was pretty damn good and warranted further investigation even if the 1.8" 3 shot group at 100y from the charge ladder did leave me feeling a little concerned.
I put the group out of my head and set about loading a seating depth ladder 10 steps, 3 rounds loaded at each step, 3 thou difference seating depth between steps so 30thou difference from closest to jam to furthest from jam.
I went back to the range and set about getting things set up, today I decided not to run the magnetospeed on the barrel as I wanted to make 100% sure there were no external influences that could affect the harmonics, especially as the barrel is an extremely light weight profile and fluted as well.
Immediately right from the first load (which was 3 thou shorter than the charge weight ladder groups) the groups were better, they sort of fluctuated a little then at 12 thou into my seating depth ladder they tightened right up to .8" then 15 thou .5" 18 thou saw the group back out to .7" as did the next 3 groups after that slowly increasing in size again but all sub moa.
Then at 27 thou it shot a .2" clover leaf group, the last group after that was only 2 rounds as I ran out of prepped brass but it opened back out up to 1.1".
So in conclusion I will settle on the 15 thou group that was .5" and some might ask why not the .2" seating depth and my reason is the .5" group was right in the middle of a big stable node of sub moa group producing seating depths from 12thou-27thou the last group in that node was the .2" group before it opened right out to 1.1" just 3 thou deeper so my logic is that the .2" group is right on the very edge of that accuracy node where as the .5" group is closer to my jam and has good grouping over 15 thou of tolerance so is right in the middle of that accuracy node.
Whilst this may come accross as tedious and OCD it definitely works, the other issue is that the factory trigger on this rifle is a heavy bitch and will need sorting I suspect it will be easier to shoot good groups once I've had the trigger lightened.
All in all happy to have a nice accurate load sorted. I will load up 6 or 9 confirmation loads to krono for velocity validation as I didn't krono the seating depth ladder.
End result should see 178gn eldm's at a velocity in excess of 2950fps.
I'll post pics of the charge ladder and seating ladder later this evening

Wats the rifle and history?
Pics?

Originally Posted by Tahr

Wats the rifle and history?
Pics?

Weatherby mk v ultralight in 30-06 ackley improved, barrel is a factory unfired 30-06 springfield that has been reamed to ackley improved.
I have swapped the trigger out with a lighter one, so hopefully I can get back to the range on Monday and verify. At suggestion ftom a mate I have loaded 5 rounds at my chosen seating depth and 5 rounds at 6 thou further into into the node just to double check.
I have also loaded up 5 extra rounds of each for krono purposes only once the load is chosen

Originally Posted by dannyb

Weatherby mk v ultralight in 30-06 ackley improved, barrel is a factory unfired 30-06 springfield that has been reamed to ackley improved

Sounds primo. Pic?

Nice, you won’t be disappointed with the decision to go Ackley Improved.

Originally Posted by Tahr

Sounds primo. Pic?

I'm trying but there appears to be an issue uploading pics since the forum upgrade overnight @DAF when i try yo upload pics i get a pop up saying "nzhuntingandshooting.co.nz says .jpeg file upload failed"

Originally Posted by Tahr

Sounds primo. Pic?

ask and you shall recieve




here is the seating depth ladder.....after tallking to my mate Jock he reckons I should also try the seating depth at .644 again as well, so I have loaded up 5 at .650 and 5 at .644 his logic was that the .644 was right in the middle of the node as opposed to the .650 which is actually closer to the front of the node.
either way which ever shoots better will be the depth settled on, I have also swapped out the trigger for one that has been fettled by a gunsmith to remove that challenge.

looks great..a few 180grn round nose for walking in and another couple of cast lead loads with charge of trail boss up thier bum for finishing anything off or the young lasses to shoot a cheeky hare with and you will be sorted LOL...

Hard to go past that 0.638 grp.
The paint job of the stock looks great too.

Originally Posted by chainsaw

Hard to go past that 0.638 grp.
The paint job of the stock looks great too.

yes at a glance, but it's right on the edge of the node, the very next seating depth just 3 thou deeper opened out to about 1.2" so I'd be more inclined to go somewhere in the middle of that node which is what I've loaded my 2 lots of confirmation loads to 1 lot at .650 and 1 lot .644 I have also swapped out the trigger for one that has been lightened and polished.

the stock finish is a matte gray over textured paint, with gold and white marble effect finsh. pretty happy with it, I also fitted a new limbasver, javelin flush cup and free floated the barrel it's come up great