Pressure Test Retumbo Vs N570 .338 Norma Improved

[bbhank]

I was running Retumbo in .338 Improved and thought it ran pretty good. I had settled on a load that ran about 2850FPS with high single digit SD's for 5 round groups with the occasional 12-15 SD 5 round group.

The first photo is the is the Retumbo pressure test which had like 7 inches of vertical dispersion,

The Second photo is the N570 and the total vertical dispersion was 2.02" and 24 of 27 rounds shot a 1.3" group. This is with an ES of 199.2. The N570 was slower than the Retumbo, however I don't have any pressure signs. The problem is I cannot fit anymore N570 into the cases.

The Rifle is an ARC Mausingfield, K&P 8 Twist Barrel, Foundation Stock, TT trigger, Area 419 Brake!


Anyone else get pressure test results that look like this?

 

[FredHammer]

I just got done with N570 and 170 in 300WM. They are grain for grain equivalent for pressure/velocity. You could get more N170 in the case with the normal sized kernels. Not those Tic-Tacs of N570!

 

[Slides]

I was running Retumbo in .338 Improved and thought it ran pretty good. I had settled on a load that ran about 2850FPS with high single digit SD's for 5 round groups with the occasional 12-15 SD 5 round group.

The first photo is the is the Retumbo pressure test which had like 7 inches of vertical dispersion,

The Second photo is the N570 and the total vertical dispersion was 2.02" and 24 of 27 rounds shot a 1.3" group. This is with an ES of 199.2. The N570 was slower than the Retumbo, however I don't have any pressure signs. The problem is I cannot fit anymore N570 into the cases.

The Rifle is an ARC Mausingfield, K&P 8 Twist Barrel, Foundation Stock, TT trigger, Area 419 Brake!


Anyone else get pressure test results that look like this?

View attachment 8341193View attachment 8341194

Is that similar velocity or slower. If there is a significant barrel transit time/MV difference it's not the "powder's" fault so much as system response at that velocity, unless they are printing different at the same velocities?

 

[bbhank]

Its at similar velocities however I was hoping the N570 would be faster!

 

[secondofangle2]

without more info on charge, velocity, seating depth, it's hard to provide any guidance.

In general N570 will give you 50+ fps more than retumbo, and it will also decrease your barrel life by 33%

 

[Bobby Ball]

I've got chamber pressure measurements for both in similar powder charge weights. I'll post them when I get home.