Hmmm... what's going on here?

[Lefty Trigger]

27.5 - 30.2 in a 26 inch 8 twist barrel .040 off lands. The 30.2 load bucked the wind the best @3050 FPS. This was shot @300 with a 10 - 15 mph tailwind. three sighters and then adjusted down 1 and left 1 for the last 17. I was holding a bit left becasue of wind switches and the group center was right on my aimpoint. The orange circle is a 3 inch stick on

edit went back and looked at the same load in a 29" barrel that I did a bit more chrono'ing on and between 28.0 and 30.0 all but one load had single digit SD's and ES below 20. Seems the sweet spot for that bullet is 3050 FPS for both rifles, it took .2 grains more in the 26 incher to get me there

I have played around with it using the Sierra 60 "Varminter" bullet in a 12 twist and got some awesome numbers but really should not have shot my test loads because we had a crazy strong wind from the left. At one point I had to shop and go down range and stand my target holder back up! I shot them anyway and while the groups were not great (because I struggle with the wind) at one point I was getting single digit ES/SD numbers and one load (32.4gr) gave me a never seen before load of ES 0 / SD 0,... never had that before, ever!

 

[P1ZombieKiller]

N150 and N550 are going to have different power curves, so I'm wondering if one powder generates a short-sharp acceleration whilst another generates a slow-whoosh.

It may be that whilst both propellants ultimately generate the exact same MV, the two projectiles weren't in exactly the same window of harmonics.

I nominate "whilst" as the word of the day. I think I just learned a new word to use...

 

[Ned Ludd]

What I think you can safely assume from your load development work is that the N550 loads generate far less vertical dispersion over the charge weight test range than do the N150 loads. That's about it. Because you fired a single shot each at various charge weights over a wide range of charge weights, the entire group of shots fired with a single powder cannot be "collectively" considered a developed load. In other words, you cannot assume because the whole charge weight test window group with N550 showed much less vertical than the N150 test window group that N550 is the better powder. Only if you were to select a single optimized charge weight and seating depth with each powder could you compare the two in any meaningful way. It is entirely likely that an optimized load with N150 would shoot groups that are just as tight as an optimized load with N550. At that point, you would then want to consider the the benefits and/or drawbacks associated with each powder, such as possible differences in temperature-sensitivity of the velocity, and the overall velocity attainable. As a single base powder, the N150 is likely to be the batter choice based on temperature-sensitivity, especially over long strings of fire. However, you'll probably get a bit more overall velocity with the N550. One of those attributes may be more important to you than the other, depending on your intended use.

 

[D-4297]

N150 and N550 are going to have different power curves, so I'm wondering if one powder generates a short-sharp acceleration whilst another generates a slow-whoosh.

It may be that whilst both propellants ultimately generate the exact same MV, the two projectiles weren't in exactly the same window of harmonics.

Yup . That pretty well covers it . Had a similar issue trying N-150 in a .308 ...Did not work for me , but N-530 works like a charm . The N -150 worked for my shooting bud , and it sure as Hell worked for Acyer at the F-Natls. , Like using Varget , and H 4895 . One has a faster burn rate , but you an get either to match out velocity . And one will do exactly what your target showed . Don't over-think it . Just load it , and shoot .

 

[CamTheBam]

Thanks for all the replies, guys!