Neck tension and ES

[flyingfisherman]

How do guys, a few of you may recall my latest quest of finding an accurate load for my 7-08 which has a decent velocity for 1000yds. Im doing it as a fact finding/learning exercise to be honest as i dont shoot those sort of ranges very often. Again, you may recall that my performance at 1000yds was 2.5MOA of elevation using 140gn VLDs over H4895 with an Av Vel of 2770fps, ES of high 20s and running with 4-5 thou of neck tension.

 

 

I went away and thought i would prep 20 cases of which were the same volumetric weight, same length, annealed and run them with less neck tension. I did this and found 20 near identical cases (nosler custom) which have also had a light neck turn.

 

My next step was to find out my MAX load in my rifle. I did this can came up with 42gn H4895 (this was 0.5gn LESS than where i saw the usual pressure signs).

 

I then went away and loaded 4x lots of 5x rounds with varying charge weights. the results are below...

 

Test rifle: Predator 7-08, LW 1:10 24'' SS barrel, JetZ mod

 

Brass: Nosler Custom (2.0235'') neck turned and annealed (2 THOU NECK TENSION)

Primer: Federal 210 Match

Powder: H4895

Bullet: Berger .284 140gn VLD

 

Range: 100yds

Weather: Light and variable breeze (<3mph), +9 degrees

 

40.5gn

Av Vel = 2731

ES = 50

Group Size = 0.93 MOA

 

41.0gn

Av Vel = 2724

ES = 89

Group Size = 0.485 MOA

 

41.5gn

 

Av Vel = 2810

ES = 53

Group Size = 0.570 MOA

 

42.0gn

 

Av Vel = 2859

ES = 31

Group Size = 0.920 MOA

 

 

The conclusion that i have drawn from my testing is that the ES is significantly higher than my pet load therefore its not worth pursuing this particular combination any more..

 

Going back to the reason i started this thread was: Am i right that there is an optimal neck tension opposted to the least you can get away with? As i mentioned earlier, my pet load which runs at 2770fps with 40gn H4985 and 4 thou neck tension has an ES of high 20s and an average group out to 600yds of 0.5MOA.

 

Would it be worth repeating this test identically but altering the neck tension back to 4 thou? My only concern would be that the MAX powder weight would be less than with 2 thou neck tension so i would need to find the MAX powder load again before i did the test?!

 

As i said, its fact finding and learning because i have a great load which does 99.5% of my shooting very well indeed.