Extrapolate from 6PPC and 6BR Data

[BluntForceTrauma]

I've reviewed Hodgdon's load data for same bullets and powder for 6mmPPC and 6BR Remington and their data almost raises more questions than it answers.

Figured I'd go about 1 grain heavier than 6PPC data and about 1 grain lighter than 6BR data to get 6mmARC starting points.

However, Hodgdon's data seems off in some cases.

For example, the 6mm 107gr SMK from 6PPC with 28.5 CFE at 48,600 CUP nets 2,702 fps.

Same bullet from 6BR with 30.0 CFE at 49,000 CUP nets 2,632 fps.

More powder. More pressure. Same bullet. Same 24" barrel length. Less velocity? 

Doesn't compute.

I suppose one test barrel could be "fast" and the other "slow." That's a plausible explanation, but doesn't really help us rely on the data.

Anyway, screen grabs of Hodgdon data are attached for your convenience.

Thoughts?

[Trashy]

Thank you sit for the research. I just got back from the range and in the process of up loading todays data. Please take a look at it and provide feedback.

Trashy

[grayfox]

Krys, my initial suggestion is not to use cfe as your powder example... it has its own unique pressure curve, I’d start with one of the more traditional ones, like varget or h335, etc. just a thought.

[Lemonaid]

I'm going through the same thing in reverse! Comparing the 6mm ARC data to what I'm getting in my 6 PPC. I am reducing the Max charges from the ARC by about 1.5 grains to get close to the velocity that the ARC data for 24" barrels are listed.
Perhaps someone with QuickLOAD could check if the difference in case capacity/volume is enough to be why.
Empirically when enough ARC reloaders compare their number it might point out if the Hornady data is reliable or needs adjustment.
Next Range day (Saturday) I'm testing the Hornaday 108 ELD M and CFE 223 at 27.0 grains and will post the numbers for anyone interested.

[grayfox]

Yes, interested. I too hope someone w QL could chime in. It would be a data point.
I don’t have any 6br or ppc so anything I’d have there is purely theoretical.

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We need hodgdon to get some data and post along with the pressure data.