Thread: Trying something, Eric Cortina method of load development

Originally Posted by Three O'Three

I like Erics videos except the one where he criticizes neck sizing. The comments defending neck sizing were awesome and really wound up Eric.

Iv been watching his videos for a while now. Listening to those F Open guys like him and F Class John and Keith Glasscock.. their anti neck sizing thing seems to come from the super super custom super tight chambers they use. Even when they say they are shooting a standard 284.. they aren't, it's all cut on a custom made reamer just for them. Hence the full length sizing so that the bolt closes.

Originally Posted by Three O'Three

I like Erics videos except the one where he criticizes neck sizing. The comments defending neck sizing were awesome and really wound up Eric.

about 80% of the top shooters for fclass and or bench rest bump 1-2 thou its no more accurate then neck size and your no worse off on accuracy ether
but a 1-2 thou shoulder bump is far more reliable and consistent (you don't have to bump every 3-4 shots) as eric says he is 100% correct in those statements

for something like prs you would be stupid to neck size only
having a tight one that doesn't chamber smoothly could lose you a match

Originally Posted by dannyb

You raise a valid point, I should be very clear I am no Olympic marksman this is true, but I can shoot and at 100 yards I'm confident in knowing if I have pulled a shot or not.
Your also correct 3 round groups mean zip in bench rest, however I don't shoot F class or PRS or any of that, I am just using Cortina's methods to develop a load for my hunting rifle.
If my hunting rifle shoots consistent speed and tight 3 shot groups that's plenty good enough for me.
I'm sharing my experience because the way it is explained just makes sense to me and if I can use some of his methods for developing my hunting loads and his explanations help me understand whats going on and what relationship the changes I make are showing in my groups then surely this is a good thing.

Your also right there is nothing wrong with a sammi spec load that shoots well in your rifle and if you have that great
I load all my own ammo so this opens up opportunities to improve or gain better accuracy so why not have a crack at it.
Plus I enjoy the challenge, I'm not out to prove anything or make massive claims, all my loads thus far for my rifles are sub moa some considerably even with 5 shot groups but you know what ? The deer don't seem to care much if I hit them an inch high or low or whatever so whilst this might seem a little OCD it's really just me playing and having a bit of fun so I won't loose too much sleep over it all.
Hopefully I'm learning too

@dannyb; Thanks for starting this mate. Learn't a heap. Much like you I don't comp shoot, just want to get the best out of my gear and it's fun. I operate under the principle that there is no such thing as a stupid question, so here goes; I've read quite a few references to SD in this thread, I'm in the dark. The only SD's I'm familiar with are sectional density and seating depth. Can anyone assist? Cheers

Originally Posted by RugerM77

@dannyb; Thanks for starting this mate. Learn't a heap. Much like you I don't comp shoot, just want to get the best out of my gear and it's fun. I operate under the principle that there is no such thing as a stupid question, so here goes; I've read quite a few references to SD in this thread, I'm in the dark. The only SD's I'm familiar with are sectional density and seating depth. Can anyone assist? Cheers

SD = standard deviation
ES = extreme spread

Thanks mate.

Just spent a few interesting hours in the shed. I'm working with a long action Ruger M77, Shilen barrel in 7 x 57. @dannyb I see your seating depths and jam depth, in a .270. I used both the jam method and @mickyducks old school method. The curious thing, bearing in mind my calibre, with a Nosler BT 150, old school 3.188 held on lands. Jam approx 60 thou more. Tried several different brands, all had similar results. Example Rem coreloct @ 3.100 old school. I'm thinking I must have heaps of freebore, especially when I see your .270 seating depths. The good thing, though, long action magazine. Even jam measured Nosler, above, fits in mag well. Cartridge has a long neck which is going to help too. Don't know if I can manage seating adjustments in increments of 3 thou though.

I now use a different method of finding jam, take a fired case and paint some loctite on the end of the projectile that goes in the case mouth, put the projectile in the case mouth making sure to leave it longer than your freebore.
Chamber the round carefully closing the bolt then leave it for 30 minutes to let the loctite set.
Carefully eject the loctite round and measure it for your jam measurement.
Works well and once you have your jam you can soak the round in hot water to release the loctited projectile.

Great idea, thanks. I was a bit concerned about the difference between jam length and projectile toucjing the lands. Interesting that Cortana says back off 15 thou from jam. Projectile definately going to be touching lands still. What's hard case is; I shoot the old Norma 150 grn soft point spire point, under minute of angle easy. Using a cleaning rod its COAL length is 3.100. I've actually got it seated at 3.130. Absolutely no pressure. So I guess the lands jam is the way to go. I've only ever used the guesometer, close enough is good enough. I'd only accept MOA or less though. I wonder what's going to happen with a bit of science. Thanks dannyb

I have used all sorts of methods - split case necks and close on long seated bullet, Stoney Point (now Hornady OAL gauge) method, Sinclairs tool for measuring seating depth (lies in cupboard unused), measure to the bolt face from muzzle with cleaning rod then push a bullet into the bore and measure from muzzle again deduct one measurement from the other. The last method is fraught with inaccuracies due to differing bullet lengths even out of the same batch. The Hornady method can give differing measurements depending on how hard you push the projectile fwd. Can sorta work OK if you take many measurements and then average the results.

Now I just use Alex Wheeler's bolt click method only. Extremely accurate and repeatable. Also useful for tracking throat advancement.

Only thing it won't work on plunge ejector type bolts with the plunger in place. You must remove the plunger which is probably beyond the ability of the average guy. None of my rifles are plunger eject.

Just remember the measurement is only a starting point for optimum seating depth.

Have a look here https://www.wheeleraccuracy.com/videos
Have a look at "Finding your lands".
"Clickers" is similar but is dealing with tight brass.

There's some really competent guys out there, just some of them aren't always in your face.

Will do. Thanks

@zimmer had a good watch, very informative. Going to struggle with out an accurate seating die, two calibres on thier way as I speak though. This time I also watched Cortina's video. Should have done that in the first place. @dannyb case lube on the projectile makes a huge difference. Measured jam with 5 different projectiles 3 times each one. Max variation of 3 thou. Pleasantly surprised. As soon as my flash seating dies arrive I'll be into it. Rifle already shoots two loads MOA but I've got two boxes of other projectiles that shoot OK but not brilliantly. I'll try and tune them. Got pleant of 2209. Going to do the load ladder, chrono it, then back them off 20 thou from jam and work backwards. I use 760 with the two winners but I'm sure 2209 will do the job.

@dannyb. Thanks for kicking this off mate. It's a really informative read. As a consequence my whole reloading practise has changed. I was a trial and error, hit and miss guy, because I didn't know any better. Been doing that for roughly 40 years.

Quick background; My main rifle is a M77 Mk1 long action with a Shilen barrel chambered 7 x 57. The magazine well is long enough to allow projectiles at jam length to feed.

I developed a load averaging well under minute of angle using my former method. 150 Nosler BT, 45 grn 760 @ 2550 fps. Good, but could be better. Of note, the lowest ES I could obtain with that combo, varying the load, was 21.

The current component shortage led me to googling and ringing around provincial sports stores. I picked up Accubonds, Corelocts, 140 grn Nos BT's and N204 at old school RRP's. I already had sufficient 2209 and 760.

The next step, obtain a Forster Micrometer Bullet seating die. That done, into action. It took a while, as spare time for me is a rare commodity.

I'll try not to bore with a lengthy diatribe and let the photo's speak. Except to say the ES was obtained by increasing loads by .3 of a grain. The seating depths were in 5 thou increments due to component shortage.

The ES was measured using 3 a shot sequence, with a fourth shot to verify if it looked promising. So all ES shown in picture was obtained with a four shot sequence.

Now for the proof of the pudding. Last Monday morning I put the method into practise. Rem Coreloct up first, starting with -5 off jam length.

Not bad, as I'd never been able to got the Corloct under minute of angle before. Of interest to me was that the load was 4 grains over ADI's stated maximum with no pressure signs. 2700 fps, quite respectable. Shots in sequence 1 minute apart, a good five minutes between groups. 3 shot groups due to component shortage. Fascinating to watch the pattern develop.

Next up Accubond, same morning.

I cheated a bit with this one, trying to save components. I hoped to pick up a tight spot quickly. That's pretty much what happened. Again, fascinating to watch it unfold in front of me.
Now I'm really hanging to try the Nos 140BT. Two really good loads so far.
A quick rider: I'll say so my self, without a hint of modesty, I have a reasonable trigger finger.

Thanks again mate.

I'd say job done with those 140gn ABs now go hunting. Some on here could have a chuckle at my comment.

@Tikka7mm08, that's something else I'm hanging to do