Sierra 130gr Prohunter in .270

[treeman]

I'm no expert, but if you play around in half grain increments, that should be about right for a 270. If you are in the middle of a node, 0.5 grain on either side will still be accurate, but if you are not, then half a grain could be a problem. The idea of the nodes, is that it is not only a spot where the rifle is accurate, but it is also a spot where the chosen load is in the middle of an accuracy band, so that if there is some variance in temperature or powder charge, the rifle load will still be consistent. If you are at the edge of a node, on a hot day the rifle will perform poorly and on a cold day it will be Ok, or vise versa.

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True, but from about the .270 it is considered that one grain is the increments to use. 1 gr is less than 0.5 % in regard to .270 loads - your bullets are out by more than that and your cases and your ogive more than 05 % variance is likely as while, especially with Sierra or Hornady type bullets.
One gr increments are fine, perhaps pay more attention to COL if you wish to fine tune a load.
You will find patterns and trends as you go shorter and longer, after finding a good load that is.

[Againstthegrains]

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True, but from about the .270 it is considered that one grain is the increments to use. 1 gr is less than 0.5 % in regard to .270 loads - your bullets are out by more than that and your cases and your ogive more than 05 % variance is likely as while, especially with Sierra or Hornady type bullets.
One gr increments are fine, perhaps pay more attention to COL if you wish to fine tune a load.
You will find patterns and trends as you go shorter and longer, after finding a good load that is.

With COL, on a .270, every 2mm deeper will increase the pressure by the equivalent powder charge of 0.5 grain, and every 2mm increase in COL will reduce the pressure/thus velocity by the equivalent powder charge of 0.5 grain. So if your rifle/magazine configuration will allow it, and you want to seat the bullet right out to the lands, then you may find yourself using powder charges that are very close to the max to get the velocity that you want.

[Messor]

It’s a 270 guys, you don’t give numbers based on calculations, you give numbers based on chrony readings, meaning empirical measurements. When in the mid 50’s regarding pressure, the burn rate simply CANNOT be calculated, it is what it is at that specific pressure. So we cannot say 1 grain will do this, or seating change will do that.

It’s a hunting load, and it’s Sierra.
What you do is stay off the lands, you chrony up, that is the only way.

The 270 is a shooters rifle, not a gong shooting creedmoor, you check the results on paper, not in reloading manuals or the interwebs.

[treeman]

Yes when reaching the upper pressures things become very unprecedented, as you say there is no longer a nice curve to follow.

You can still however use 1 gr increments when doing load development.
I often get the impression that people seem to forget that just yesterday we were loading these same weapons with same propellants and same primers bullets and cases, using only the cases and ears to tell us what we were doing.
We got a load from the book worked up higher loads till cases and primers told us to back off a bit.
To measure is to know - we are much luckier and safer now though.