N560 and N565 in 6.5 PRC

[Ironworker]

I shot both Hornady and once fired Federal brass at today's range session . Hornady load was 57.2 grs of H560 behind 139gr Lupua average velocity 3183 FPS SD 12' . Just under 1/2 100 yd groups ,zero pressure signs,bolt opened smooth as silk . Federal brass is 15grs heavier that Hornady 57,2 grs of V-V N565 behind 139gr Lupua produced average velocity 3,.139 SD of 9.9 and 5/8ths 5 shot group severe Bolt lift . Shinny ejector on a couple pieces. Why with a slower powder did I have less velocity out of 28" bbl. Same seating depth .

 

[FeMan]

As long as everything else is the same (case, bullet, charge weight, etc.) , a slower burning powder should yield a slower muzzle velocity. The slower powders can be capable of higher velocities but require increases in charge weights. Since you changed brass and the case volumes are different, it isn't apples-to-apples though.

I don't have a burn rate chart handy that lists N565, but looking at the burn rates in Quickload (Ba) N560 appears faster than N565. That is assuming their burn rates listed are accurate.

 

[MikeWhy]

All else being equal... What's different?

- Heavier case, thicker wall.
* Thicker wall: higher neck tension?
- 15 gr heavier case has 1.8 gr smaller H2O case volume.
* Smaller case volume: higher pressure.
* Pressed charge with smaller case volume? Check seating depth.

One would think higher pressure leads to higher MV.
It's quite the puzzle.

 

[Ironworker]

I thought cause of higher pressure,I'd get higher velocity . Yes its a puzzle. Powder charges will be decreased in Federal brass.

 

[Laurie]

I thought cause of higher pressure,I'd get higher velocity .

You're confusing peak and total pressure, ie the area under the pressure / time curve. Use a smaller capacity case with same powder / charge weight / bullet / primer etc and you increase peak pressure. A larger capacity case will then normally give rather lower peak pressure, but the option of increasing the charge weight to input a greater amount of energy and obtain higher MVs at same peak pressures.

That's with one powder, but you've changed two variables in one set of tests - case make and probably capacity; and powder grade / burning rate. Normally, you'd expect lower pressures and MVs from the slower burning powder, but other factors can change outcomes. That's why we research loads data, then do careful work-up load development in our own rifles, each of which behaves as an individual.

 

[Beiruty]

My sims say N570 is the best for heavy bullets 140-145gr for the 6.5 PRC

 

[rhovee]

N560 gets higher velocities than N565 in that case. I haven’t seen N565 do anything H1000 can’t. But N560 gets some very good speeds. It’s similar to RL26. They really poured the hot sauce on N560.

 

[ebb]

Use VV165 and save the barrel.