Trying something, Eric Cortina method of load development

So I'm trying something different.
I have been watching Eric Cortina's vids on YouTube reference "chasing the lands" and how it's a really inaccurate method of working up a load.
So for those that are un aware basically it suggests using a method that relies on an average measurement to work out distance to the lands as a reference to your seating depth may not be the best approach.
Instead he suggests seating a projectile way out in an un primed but otherwise prepped case.
Then lube up the ogive with die wax.
Put the dummy round in then close the bolt on it basically using the lands to seat the projectile.
This becomes your no go or jam distance and in fact it is suggested you go minimum 10 thou back from this.
Then load up a charge weight ladder at your maximum length (as above jam minus 10 thou). 3 rounds at each weight.
Then shoot your ladder over a chrono to asses which charge weight gives you the most consistent fps (it may seem counter intuitive but Eric suggests not shooting these at a target, so you don't get tempted to go with a charge that shoots a fluke good group when there are more consistent speeds in your ladder).
Once you have worked out you most consistent charge weight then load up another ladder starting at your max length (jam minus 10 thou) load 3 rounds then load 3 at 3 thou deeper and do this working further away from your jam at 3 thou increments.
The idea being that the most consistent speed load can be tuned by seating depth.
The most consistent speed is what will get you accuracy out at extended rounds.
There's a fair bit more to it than that but that's a brief run down.
In my next post I will show my progress as I try this method.
My current load development is based far more on a bit of knowledge and a fair amount of luck.
I have good brass prep, and consistent loading practices but getting my load usually expended on seating my projectile at 20 thou of the lands or as close as I could get if the mag didn't allow then just doing a ladder of charge weights to find the best grouping.
Don't get me wrong this has worked extremely well and I've achieved some brilliant results (probably a fair amount of luck rather than skill)
Anyway after watching Eric's videos they just made sense to me and a lot of it is in layman's terms.

So with my model 70 270win I decided to have a crack.
Out of curiosity I measured the distance to the lands with a hornady OAL gauge and got an average length of 2.780" which would normally see me seating at 2.760 for my seating depth.
Using the Cortina method I got 2.840"
My maximum mag length allowed for a max ogive length 2.7605
So in keeping this able to be mag fed I started at 2.760"
I loaded all my charge weight ladder at this length going up in .5gn increments.
I'm using superformance for something different so started at 55.5gn through to 57.5gn
I shot them today with surprising results.

Attachment 150364

Great velocity and consistency at 56.5gn and then at 57.5gn the velocity was incredible for a 270win case but I was getting very slight ejector swipe.
I have no doubt my max load could be tuned but i don't want to be anywhere near pressure.
I am going to now load up a seating depth ladder at 56.5gn and shoot them at paper to see what accuracy is like.
It was really strange shooting the charge weight ladder over the chrono without a target but I'm really keen to see how the seating depth tunes the load.
Either way 3040fps avg is fair humming for a 145gn eldx and more than enough for a good hunting round

Following with interest mate. Please post results. I’ll be trying this when my labradar shows up next week.

Yup need to load my seating depth ladder next and shoot them at paper.
May not have time to do that till mid next week but will see what time allows.
Will definitely post my results good or bad :thumbsup:

ok bud..following you so far....now an OLD SCHOOL way of doing same....use your cleaning rod with the, object removing bit on end..eg flat end....push a projectile up the chamber and hold it as far in as it will go...may need pencil...or indeed you could just seat one only just in case and hold it in place...poke cleaning rod down from muzzle and mark rod at muzzle.remove case replace bolt,close bolt and reinsert your cleaning rod right down to bolt face,again mark...the distance between your two marks is now.............pretty darn close to your other measurement...its your maximum OVERALL length.....which in my poohseventy is no bloody use to me at all as a 130grn ballistic tip will be JUST in case mouth and no way in hell will it fit in mag....so all my rounds are made 1mm short of mag length and thats it...

Interesting results, load 56.5 seems pretty consistent, but in saying that they all were pretty good. Will be great to see how seating depth effects the accuracy.

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Originally Posted by Mooseman

Interesting results, load 56.5 seems pretty consistent, but in saying that they all were pretty good. Will be great to see how seating depth effects the accuracy.

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I'm also wondering if seating depth will effect velocity, as the deeper I seat the pills surely pressure and velocity will increase ?
Then again maybe it will be negligible who knows ?

Yes I thought the same thing, just remember the hot temps could be a factor when you get up towards the top loads and when seating the projectiles deeper it may spike the pressure to much.

pressure will DEFINATELY increase if you seat deeper.....take it to other extreme and you have weatherby...long freebore so case can dump pressure quickly so can have more to begin with.....by seating deeper your case capacity is less...again to extreme a 30/06 load in 308 case...

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Originally Posted by Mooseman

Yes I thought the same thing, just remember the hot temps could be a factor when you get up towards the top loads and when seating the projectiles deeper it may spike the pressure to much.

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Yup all over it, won't be going anywhere near the hotter loads just wanted to know for reference where I started to get signs of pressure.

Yep seating depth has a huge effect on grouping. As far as im aware its all to do with at which stage of the barrel harmonics that the bullet is exiting the muzzle.

From the seating depth testing ive done with various rifles and loads, the difference in grouping can be considerable.

My most recent test (last week) with 65gr SGK's in a model 7 223. I loaded several groups, starting at .005" off the lands and going to .030" in .005" steps. All but one shot at .6-.7 moa, .015" off the lands shot .25 moa.

Id already worked out what powder charge to use from ladder tests, and some group testing at whatever coal i started at.

Clearly this particular bullet in this barrel isnt that fussy, ie .6 moa isnt too shabby, but i'll take less than half of that any day if its available just by tuning seating depth.

Ive loaded up a bunch more at that coal and charge to test further to make sure it wasn't a fluke.

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Originally Posted by GWH

Yep seating depth has a huge effect on grouping. As far as im aware its all to do with at which stage of the barrel harmonics that the bullet is exiting the muzzle.

From the seating depth testing ive done with various rifles and loads, the difference in grouping can be considerable.

My most recent test (last week) with 65gr SGK's in a model 7 223. I loaded several groups, starting at .005" off the lands and going to .030" in .005" steps. All but one shot at .6-.7 moa, .015" off the lands shot .25 moa.

Id already worked out what powder charge to use from ladder tests, and some group testing at whatever coal i started at.

Clearly this particular bullet in this barrel isnt that fussy, ie .6 moa isnt too shabby, but i'll take less than half of that any day if its available just by tuning seating depth.

Ive loaded up a bunch more at that coal and charge to test further to make sure it wasn't a fluke.

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Yup Cortina states any load can be tuned by changing seating depth and shows targets shot showing where the nodes begin, peak and taper off.
He also states that there may be multiple seating depth nodes and dome are larger than others so you need to do a comprehensive seating depth ladder to find one of these larger nodes as they will be more stable and more forgiving to tolerances created by limitations of loading gear and to an extent the skill level of the person loading.
As previously stated I'm sure a lot of this is not new or ground breaking, just the way Cortina explains it makes sense to me.
It's really very Interesting seeing the results learning how my changes influence the results and why, also understanding how to interpret what is happening especially in the seating depth ladder.

https://i.ibb.co/Lzyp2X7/Screen-Shot353.jpg

The 56.5gr load looks good. Low SD, low ES but would be nice if speed would have been closer to the loads on both sides. Ideally around the 3015 or so. Might pay to load up again and get more data points? Definitely a load you would like to see how its grouping on paper and to invest time into seating depth differences.

@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.

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Originally Posted by ebf

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

IT WORKS...



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

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Yup quite a few people have looked at me like I've lost the plot when I tell them I shot my ladder today but didn't bother shooting it at targets :D