Powder is new, less than 2 years old.
I'm not concerned about the powder, only what GRT is showing relative to what I can infer from Nosler's and Hodgdon's load data.
Hodgdon is showing 55 gr of IMR4831 under a NP 175 as generating 61K PSI, but that's using a Nosler case, presumed water mass of 74 gr (that shows 64.9 gr of usable space under the bullet in GRT, which tracks with what Nosler shows).
GRT is showing that same load at 49K PSI
Pretty sure the issue is with GRT.
With the 160 gr A Frames, I started at 55.7 gr IMR 4831 and progressed up in .2 gr increments to 58.5, COAL of 3.33 (which I think is too long by a little). GRT says I should have been around 2825 at the top end, but my magnetospeed showed me right at 3K fps on the highest load. No signs of pressure on the brass or anything.
I'm not too concerned about over-pressuring on the 175s, will take the same baby steps to progress up, just seems odd to me the disparities I'm seeing.
One thing for certain with 160 gr SAF....my rifle seems to like pushing them pretty hard. Both of those 4 shot clusters are over 2900 fps, one almost 3K fps.
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