Thread: Trying something, Eric Cortina method of load development

When I posted earlier about the feeler gauges, I should have said that I used them with my comparator inserts and calipers. As calipers are not accurate like micrometers are, I figured 3 thou of feeler gauge is a real 3 thou. So leaving the calipers fixed at one setting and measuring the increases in seat depth with feeler-gauges

Measuring the desired length is one thing. Getting the same length from your seating die less the 10-20 thou etc consistently can also be a challenge.

finally picked up the Winchester mod 70 today after waiting weeks for a replacement firing pin.
Will be re starting this process in the next week.
I have a box of 140gn berger VLDH
and 1 box of 140gn Nolser partitions
I may seat the partitions to sammi spec, but the Berger VLDH I will be doing the full seating depth test after finding the most consistent speed charge weight.
I also have a box of sako gamehead ammo to run through it for shits and giggles just for comparison.

Originally Posted by Rated M for Magnum

It's very hard to argue with Eric's results. I watched his video about neck sizing vs full length sizing and thought, alright I'll give it a go. It made a bit of a difference. These are two 3 shot groups shot about a month (possibly longer) apart, from the same rifle ( Howa 1500 308), same
type of projectiles from the same box, same powder from the same bottle, etc.

What I'm getting at is the only difference was I full length sized the brass and the group size halved. I know 3 shots is only indicative and maybe Jupiter was fully aligned with Uranus for the second group on the left, but...I'm converted. I'll be full length sizing for this rifle from now on. Attachment 150656

If i were examining this i would be thinking the group on the right just had slightly too much pull into the shoulder. Note how your vertical dispersion is almost identical.
Howa 308s are like this with light projectiles flat base. Its hard to shoot em badly at 100m.

Right after a bit of hiatus this is back on.
I did the jam measurements and got 2.858" with 140gn Berger VLDH
My mag in the mod 70 allows for 2.843" which just happens to be 15thou off my jam and seems like a great place to do my charge ladder.
All above measurements are ogive length not COAL.
After cleaning, annealing, prepping and priming 150 cases yesterday I'm ready for a range session.
I have 18 rounds loaded for my charge ladder, hoping to get to the range in the next day or so.

I also slapped together a load for nosler 140gn partitions the other day.
Got an avg speed of 3000fps and E.S of 16fps with a load the shot just over 1" at 100 yards so I'm pretty happy with that for a low tech non pointy drop anything on the spot load.
I've loaded up 5 more for confirmation and I'll shoot them at the range when I get a chance too.
If the partitions shoot around an inch I'll be happy as.

How did 61.5, 62 and 64 group?

Originally Posted by JaSa

How did 61.5, 62 and 64 group?

Up to 63gn they all shot pretty much the same, they started to open up at 63.5gn and I started to get pressure at 64gn so settled on 63gn
Aldo anything over 63gn was compressed so I'd rather stay away from that if I can.

Cool.
Looks like a pretty forgiving projectile to load with a big node from 61.5 -63.0gr. 63gr is a good choice in that case. Could even back down to 62.5 if you shoot within a big temperature range throughout the year.

Originally Posted by JaSa

Cool.
Looks like a pretty forgiving projectile to load with a big node from 61.5 -63.0gr. 63gr is a good choice in that case. Could even back down to 62.5 if you shoot within a big temperature range throughout the year.

It was a pretty hot day when I shot the ladder I'm comfortable that it would be safe in any weather

I suspect the Bergers will ve far less forgiving, but thats ok I don't mind fiddling with them to get them shooting, I also have some of the 168gn to try in my rem mag so got a fair bit going on at the moment

wow....3000fps with 140grn partition and its grouping inch.......hmmmm methinks I may just have to try some of this H1000...... thats got to put a world of hurt on any deer out to 400 yards with ease....

Originally Posted by Micky Duck

wow....3000fps with 140grn partition and its grouping inch.......hmmmm methinks I may just have to try some of this H1000...... thats got to put a world of hurt on any deer out to 400 yards with ease....

Ummmm I mean shit it's no good sprays around like a shotgun

LMFAO..... shhhh your secret safe with me...

Ok charge weight ladder results:

61.5gn 2966, 2967, 2922

62gn 2957, 2957, 2963

62.5gn 3030, 2976, 3012

63gn 3010, 3054, 3037

63.5gn 3059, 3051, 3052

64gn 3133, 3075, 3097

They all shot pretty good but far the best was the hottest which shot under 1/2 inch, which was surprising considering the E.S the velocity was all over the place.
I think I'm going to try a full seating depth ladder at 62gn which gave an E.S of 6fps and shot .9 inch 3 shot group.
I was going to do a seating depth ladder at 63.5 but the problem with that is that it's already a compressed load so I don't think it's a viable option.

What is interesting is that some of the loads with a higher E.S actually shot tighter groups, I can see why Cortina doesn't shoot is charge ladder at paper, it would be easy to be sucked into less consistent load (velocity wise).
As Cortina says group size on charge ladder is irrelevant.
Here is a pic of the best group I got today, aside from the fact it's very compressed it would be easy as a novice to look at that and go "job done"
But the E.S on that load is 58fps and who knows how erratic it might be over a larger sample this was only 3 rounds....
The load I am going to "tune" has an E.S of only 6fps which if I can get it to group better will be far more reliable when working out drops for longer shots, as it stands that load already shoots under an inch (.9") but I think I can get it better with some tuning.
Here is the half inch sucker group for reference