Alliant Power Pro Varmint
This power is similar in burn rate to perhaps, Accurate 2460.  The load data for Accurate 2460 is in the ballpark.  This powder is about as close to the "best" all around power you can buy for 5.56 as humanly possible.  It can do lighter bullets, it can do heavy, it can do it ALL.  Do not stop by GO and collect $200, go straight to the store and buy this, now.

This page is dedicated to this U.S. Marine "POGMarinesFPS The reloading bench"  He likes Varmint too!  For those not aware, a "POG" is basically a term that means your not a "grunt" or a front line Marine, your role might be support, logistics, headquarters, etc.    Look him up on YouTube HERE  (click on HERE)
Berger 77 OTM cases
23.6 top, 24.2 bottom.  Not bad.
Alliant Power Pro Varmint
This is a fine "flattened" sphereical powder.  This powder fits very densely into a case.  This could be the wonder powder for 223/5.56.  This could be it.  We have tested no other powder than has done velocites with the brass as good as it looks, than Varmint.  I believe the explanation for why the powder is superior to other ball powders in Standard Deviation, etc, is because the others are a pure "ball", totally round shape to them.  These are FLATTENED speherical.  Flattened spherical is more consistent burn characteristic apparently.  Which makes sense.  
Lets highlight the cases
How can this powder do velocites 2900+ FPS in 75 grain, without blowing primers, or massive case head stamp issues, or huge brass burs, etc?  This is a wonder powder..lets look at some brass from the:
24.8 grains 2.255 OAL on left (2900 FPS)
25.0 grains 2.255 OAL on right (2930 FPS)
I just do not understand it.  Those primers are not even that flat.  They have small ejector side indication, but its mild.
More cases
24.8 grains 2.255 OAL on left (2900 FPS)
25.0 grains 2.255 OAL on right (2930 FPS)
These are the 2 worst looking brass from this lot.  The ejector swipe is NOT a bur that is sticking up, the brass surface is not jagged, its smooth.

This is WAY WAY over max pressure.  But why is the pressure not showing up like it should?

This might be the hunting round of the century.  1430 lbs of energy, 75 grain Hornady bullet going 2930 FPS from a 20" barrel?  That is very very powerful.
Some robots can run
Right click picture to see "view background image" for more detail.
Some minor ejector marks, but nothing even what I would call "medium or very bad".  Since there is no load data on this, its hard to say how "far" over maximum these are, but I can almost guarantee the Berger 77 OTM is at least ~1 grain over maximum.  Berger 77 OTM is like ~30k or so longer bullet than comparable Nosler CC or Sierra MK.  So its sticking way down in the case compared to those, thus it cannot accommodate near the same loads, the pressure will be much higher.
26 grains with 55 is not near ceiling of how high this can go, but that is already way past maximum loads.

Do not load over manufactured rec, and if you do, it is your responsibility solely, of course.
Alliant Power Pro Varmint
Here we go again with the groups.  If by this point, you don't think holding a "tighter, exact spot" at 50 yards versus 100 is better for testing, here is another target with really tight groups.  We chose 50 because the groups at 25 with some were through same hole, and its hard to measure anything from that.

Onto the powder.  Is this the wonder powder for 223?  The hidden gem?    Let me take this time to "advise" Alliant company. 

Whoever knows Alliant, please pass this on.  "Hey, Alliant, I think you could have the "best" powder lineup of anyone out there.  But you have one issue for improvement, your load data is very weak.  Please, go learn from Western Powders on how to build a load guide.  They are masters.  Your load data for Varmint?  you have like only a few bullets and its near 55 grain only?  What about 62 grain, 69, 75, 77, 80 and a few variants of popular 55 grain bullets?  You should also list what other powders your Varmint, for example, is "close to" in terms of burn speed.  you could do SO MUCH MORE!  You have probably the best product, but your marketing needs improvement.  Take varmint for example.  It could be the top selling powder I think for 223/5.56.  Right now, people think its like H335 or something like that.  But H335 cannot compete with Varmint "overall".  Nobody even knows about this powder.  Come on Alliant, lets step up the marketing effort, you can do it!"
Some of the Loads we tried
Load at your own risk.  What we load doesn't mean it will be safe for you. Do not load above recommended manufacturer book maximums.  2933 FPS from a 75 grain in 5.56 is way above book and high pressure.  But look at the brass? It doesn't even look that bad.  How can that be possible, is this a wonder powder?  How can I do 25 grains using a 75 grain bullet when Alliant says 25.x is the MAX at 55k PSI for 55 grain?  This powder must be very very pressurre stable.  Its flatly, ridiculous.  1,430 LBS of energy in a 5.56?  That is ridiculous.

Look at the STANDARD DEVIATION of this powder!  What the heck!  How can a spherical powder consistently do UINDER 10, even 7 SD?  That is unheard of.  Of course our method is very good, but even so.  Other Spherical powders did not come close to this one.