Alliant Power Pro 2000 - MR
This power is not ideal for 5.56 overall.  This is because you can load over 30 grains for lighter bullets.  That is too much as most of the cases we use are under 30 grains.  This power is what we think, the SLOWEST burning powder that can be reasonably used in 5.56.  For example, what you would use for 69 grain bullets is similar to what you would use for Varget using 55 grain bullets.  Its even significantly slower than even Accurate 2520, which is on the slow end for 5.56.  If you want HIGH VELOCITY in heavier bullets for 5.56 such as 69-77 grain?  Then try this powder.
Bottom 4 are the Berger 77 OTM loads...
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Alliant Power Pro 2000 - MR
This is a fine sphereical powder.  This powder fits very densely into a case.  Of note, this is not a traditional spherical powder, like AA2230 or AA2460, or etc.  THis is a "flattened Spherical" powder.  This could explain why the SD is lower than the traditional "ball" shape powders.  This has a slightly more consistent burn characteristic, perhaps.
Brass
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Some pressure signs, minor, started to show up in the 25.6+ Berger 77 OTM loads with tiny ejector area impressions.
Alliant Power Pro 2000 - MR
It really liked the hotter load of the 25.8 Berger OTM.  That is a very tight group.
It didn't like the Nosler CC in those load volumes, but the 69 grain did better.  There is no point testing this powder with 55 grain, you would use this powder for 69+ Grain bullets "generally".  Of course you could use it for even 40 grain bullets, but you just won't get the velocity compared to say...Power Pro Varmint.
Some of the Loads we tried
Load at your own risk.  What we load doesn't Blue highlighted rows are commercial, premium bullets for comparison.  Good velocities.  Very good Standard Deviation, once again from Alliant.