Ok.  After about 2 years of thoroughly testing almost every reasonable 5.56 powder you can buy on the market, we have decided what the best "all around" 5.56 Powder is.  It is Hodgdon Benchmark.    Read on to see why...

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Some "Premium" loads
In order to understand what powder is top tier, you have to directly compare it to other powders that are comparable.  Alliant AR Comp is comparable.  AR Comp, we rate #2 best powder for 5.56 you can buy.  Here we can see, 3 different bullets, in 2 different rifles, same loads..compared..
55 Grain Sierra Blitzking
55 Grain Hornady V-Max
55 Grain Nosler FB Tipped

All very similar bullets.  And we can see...absolutely lights out accuracy from both benchmark and AR Comp.  Similar results, but Benchmark is marginally better, because its barely more consistent we think in results..
Benchmark Best of the BEST
Lets discuss why this powder is stand out in the 5.56 world.  What makes a powder stand out and overall "best"?  Here is how we define "best", and this is no industry standard, this is just what we think, after basically using about ~30 different powders in 5.56.  We have the basis now to discuss what makes a powder good for 5.56.  Before we get into it, we just want to say, that one can "use" almost any powder for 5.56 and make it "work" all the way from N130 or Reloader 10x, which are on fast side, to the far other side, which would be SW Precision Rifle, Varget, RL15 or Alliant Power Pro 2000-MR.  But the super super fast powders and the super slow powders in the range, although can work in 5.56 in "some" ways, they are not designed to work in all weight bullets, and thus, are recommended for different loads.  Reloader 10x, or N130 might be good for say 40-50 Grain bullets, but above that, too fast.  Just like Precision Rifle and Varget can work for 55 grain bullets, they are not very good for that weight, and best suited for 69 grain and ABOVE in weight.  The powders with medium burn rate in the 5.56 range, such as Benchmark, H335, AA2230, AA2460, TAC, Power Pro Varmint, are better "overall" choices for wider range between 50-77 grain.  This is why we only tested like 30+ different powders, because many could be used, but why? When you can use 30 that are better suited?  Here are the criteria we used to say what is the best:
MAJOR REASONS
  • Good velocity using 50 grain bullets to 77 grain bullets
  • Case fill:  Does it need to compress to load 50-77 grain bullets?  If so, how much?
  • Accuracy:  How is its accuracy consistency compared to others?
  • Temp stable?  How temperature stable is the rifle powder?
MINOR REASONS 
  • Cost
WHO CARES?
  • Metering
We don't care, and most don't care we would guess, about metering, because a lot of people "hand" meter, and charge 1 at a time, carefully.  If you do this, metering means nothing.

Reason #1 Velocity:  If you look at a reloading book for 223/5.56 you will see using ~50-65 grain bullets that Benchmark is near top velocity, or it IS top velocity at same pressure.  So its top tier here.  Now other powders can compete in the velocity front with Benchmark.  Some are AR Comp, but most notably, what we think is pretty much "King and Queen" of Velocity in 5.56 is Accurate 2230 and Accurate 2460.  Accurate 2230 can be loaded to near 26 grains using 55 grain bullet and that is up around 3300 FPS in a 20" barrel.  That is top tier.  Accurate 2230 has "similar" burn rate to Benchmark and AR Comp as well. 
Reason #2: Case Fill.  Benchmark, using a 55 grain bullet would slightly need compression, but no big deal at all, when you use max charges of near 25.5 Grains.  And you would not use 25.5 grains of powder with a 55 grain bullet, because it is far more accurate and great velocity using 25.0 grains, across every gun I ever tested, every 55 grain bullet.  And using 60 grain V-MAX, 60 grain Berger and 62 grain bullets, it still liked 24.5-25 grains of powder, which we think is still under or near max load and lights out accurate.  Benchmark is like the "perfect" fill in the case, with almost every bullet you can put in the rifle, that is 50-77 grains.    Accurate 2230, since it is a small grain ball powder, as well as Accurate 2460, have better case fill characteristics than Benchmark or AR Comp.  You can put 27 grains, for example, in a 50 grain bullet, loaded to NATO pressures, but you cannot do this with Benchmark or AR Comp because those powders start overflowing the case when you get near ~25.5-26 grains depending on what case you are using.
Reason #3: Accuracy.  This is where Benchmark starts to run away with the title.  Accurate 2230 and Accurate 2460 are arguably better Velocity and Case fill than Benchmark or AR Comp, but they are simply not as accurate as Benchmark in our thorough testing.   AR Comp is "comparable" but we think its just marginally less accurate, and when you test dozens of back to back, same gun, same load tests on same day, you start to notice it, slightly.  Benchmark is simply top top tier in Accuracy using 50-65 grain bullets.  I have achieved top accuracy using 55 Grain Blitzking, 55 grain Berger, 55 Grain Hornady V-Max, 55 Grain Nosler FB Tipped, 55 grain Hornady FMJ, 60 grain V-MAX, 60 grain Berger, 62 Grain Speer Gold Dot, 64 grain Game Changer and Game King from Sierra and its great accuracy using 69 and 77 grain Sierra Match King.  Although for 69-77 better powder choices would be Varget, or Shooters World Precision Rifle, or IMR 8208 XBR, or Reloader 15, or Norma 203B in our view, although those last 2 are less temp stable. 
Reason #4:  Temp Stable.  This is only important with Rifle, and only really an issue when you are shooting past a few hundred yards.  So for Hunters who take game from 50-200 yards, this doesn't matter hardly at all.  The longer range, the more it matters.  For example.  A non temperature stable powder, such as CFE 223 has large change in velocity every single degree F change.  So CFE 223, over a 100 degree change in temperature, would be somewhere around ~175 FPS change.  175 FPS change?  That is gigantic bullet drop difference.  Take a powder that is temp stable, such as Hodgdon Extreme Powders, or something moderately temp stable, like Ramshot TAC, you have much less affect.  Benchmark for example, over 100 degrees would be slightly under about ~50 FPS.  50 FPS is less than many people's reloads extreme spread.   That is near as good as it gets.  Here are some temp stable powders for people that don't know:
Varget, Benchmark, Hodgdon 4350, Hodgdon H4895, IMR 8208 XBR, AR Comp, Reloader 10x, Reloader 16

In our view, if you are a rifle user, there is "zero" downside, except maybe price, for picking a temp stable powder, as they are superior to non temp stable powders, overall.  Benchmark is not the most temp stable, perhaps H4350 is, then Varget, but its good enough.  Now you know why H4350 and Varget are so insanely popular.  BUT, Shooters World Precision Rifle, we think is better than Varget, and temp stable as well.  Please consider this. 
MINOR REASONS
Reason #2: Cost?  Temperature Stable powders like Benchmark, are typically $5 or so more per pound then non temp stable, generally.  Hodgdon Extreme powders are top tier powders.  Benchmark is one of them, and also similar H4895 is another one.

This is our opinion after testing nearly everything, and re-testing, and re-testing, and over and over out of many guns. 

Benchmark.  KING OF THE 5.56 POWDERS.  Here is a ranking....of our personal favorites...top 10 probably...
  1. Hodgdon Benchmark
  2. Alliant AR-Comp
  3. VV N133
  4. Shooters World Precision Rifle
  5. Hodgdon Varget
  6. Alliant Power Pro Varmint
  7. VV N135 probably
  8.  Winchester 748
  9. Accurate 2230
  10. Ramshot TAC
Honestly when you get down to #6-#10 those are all like toss up and good for slightly different reasons. 
Powders we don't recommend for 5.56?  They can be used, but issue with them is listed
  1. H322 - Too fast (burning)
  2. VV N130 - Too fast
  3. Alliant 10X - Too fast
  4. Alliant Power Pro 2000 - inconsistent results, extreme spread
  5. Hodgdon CFE 223 - inconsistent results, extreme spread
If you liked this explanation, please donate to our site so we can do more in depth studies on your favorite powders for 9MM, 5.56 and Valkyrie.  Thank you!
16" Proof Research Carbon Fiber Barrel  100 yards
Three powders, and 1 winner.  Benchmark wins again.  Now, its understandable if you don't count first shot, or last shot out of AR15, as it could be off slightly, but if you could the best 4 shots, in each group, that makes Benchmark win even more, on Average across all.  As many other groups have 2 shots outide main group, or more.




20" Shilen WOA Barrel  100 yards
Hello?  That dead center group with the first shot of the volley being out of main group is still the best group, by far out of all, and the other 2 groups are right near MOA.  But now we can also see why AR Comp is so dang good.  It can compete in the Velocity and Accuracy department most of the time, with Benchmark. 
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