After our test in 5.56, we knew this powder was going to be good in Valkyrie because Reloder 16 was good in Valkyrie.  And if Reloder 15.5 uses pretty much 2-3 grains less, and is basically same density/case fill, then its going to be ideal for the cartridge. 
Here is a summary of good points about this powder
  • Low SD's
  • Low ES's
  • Good groups for random loads, not tuned
  • Loads are not compressed much at all, great case fill to do what you want
  • Of course its very temp stable, that is what the TS is.  "Temp Stable?"
  • For Valkyrie this and VV N540 are the go to powders

Reloder 15.5 Testing
Very nice neck turned brass
In Valkyrie, the compression is minor, so you don't mark up  the ogive seating the bullet
Federal GM Primers

We neck turned it all
Typical neck thickness for Starline Valkyrie  brass is 14-14.5k thick at thickest point, generally.  We turn it so is around 13.3-13.7k uniform all the way around, with give or take about .0004, or 4/10 of 1 thousands. 
Reloder 15.5 Valkyrie
200 Yards
We did 2 control groups, using Reloder 16, same brass, 26.5 grains, as this load is already established as consistently good.  And it did it again.  @ 200 yards out of the AR, 1.5 & 1.6 is great, we will take that.

Reloder 15.5 is another story.  It has better potential than the Reloder 16 because you can fit same amount in the case as the Reloder 16.  So since Rl16 we were using 26.5, you can see there is a lot of space to go.  This makes RL 15.5 ideal for Valkyrie.  And seeing that we got the 80.5 Full Bore's to do excellent 1.3" group first time out, with no tuning, that is as good as we could hope for.  The ELD-M Hornady matched the RL16 load too, at 1.6".  Not tuned.  So great potential.  And look at that:

RL15.5 24.0 grains is about 2664 FPS
RL 16 26.5 grains is about 2664 FPS

2.5 LESS grains to get same velocity.  That is great. 

This barrel is a Rainier 22" Ultramatch 2.  Its like 1:7.5 twist, so perhaps the 85 RDF a little outside ideal

So we have a winner here folks.  Reloder 15.5 is great for Valkyrie with large potential.  Take a look at the data below.

We got 4.7, 5.0 and other single digit SD's. with 2 ES of 12!  that is really top tier.  With tuning, it is sure to be consistent around 10 SD, and ES around 20 (if you shoot enough bullets)  That is all you could hope for in a powder, and in a narrow class of powders that can compete with that elite area.

Perhaps the largest competition for Reloder 15.5 is simply VV N540. 

More RL15.5 groups  this time 100YARDS
A couple good groups.  Look at data below.  really insane SD's and ES's here.
Reloder 15.5 Valkyrie Data
We have a winner powder here in the SD and ES area folks.  Low SD's except 2.  Good ES on majority, and several groups have potential with a few already good. 
Also, RL15.5 is good velocity.  Already in mid 2700's with what I would call pretty standard loads, not even pushing it with a 22" Barrel.  2800+ FPS with this powder will be super easy with 22" barrel. 

2.7 and 3.3 SD with ES of 7 and 8 on 2, 5 shot groups? That is as good as it gets.  I don't think I have seen that before to do multiple groups under 5 SD, it was like every other group for first 7 groups.

Please do not compare accuracy of Valkyrie to 5.56, because its not comparable.  5.56 is less picky with loads, and far more accurate in our opinion.  Getting some .6-.7 MOA first time out is really good for this cartridge. 
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