powder and bullet weight relation.

[TexasHaag]

If loading 3 different bullet weights for the same rifle, a 175, 200, 220 and IMR 4227 for subsonic in a .300 AAC Blackout. The data to me is conflicting.
the 190 shows 10.4c, the 208 is 9.8, and the 220 goes back up to 10.1...
Question? why does the heavier go up in powder.... Logic says lower still, maybe 9.5?

These are all subsonic the numbers came from Hogdons subsonic load data...
I know to start high and work down.

175gr, 4227 10.0gr
200gr, 4227 9.8
220gr, 4227 9.6

what does the collective say?

thanks
texashaag

 

[Bmghunter]

Probably start low as you say. I think the oddness related to the shape of the bullet and their ogives which will hit the lands at different times which causes the pressure to spike differently so the heavier might spike slower therefore a higher charge is ok? All is a guess.

 

[Evintos]

Bullet bearing surface length can affect pressure. Looking at weight alone wouldn't give an accurate picture of what the bearing surface would be.

 

[Doom]

Your sub's are not driven by pressure but by velocity to remain subsonic. It appears that the idea is to stay around 1050 fps.