Are these better for the 10.5" than slower burning powders like BL-C2 or RL-15?

Burn rate depends on the bullet weight.  Not barrel length.  Peak pressure happens after 1.5-2" of initial bullet travel.  Peak pressure also happens after complete ignition and corresponds to the fastest generation of gas.  Smokeless propellents burn faster with increasing pressure.  So complete burnout happens shortly after peak pressure, in the .223 Rem, that is about 8" of bullet travel with the slowest propellents.

a bit confused by your post.

I presume you mean a 10.5 inch AR.

What bullet are ya loading?

What is the intended use for this load?

I have had good luck with Reloader 15 and H335.  Started testing H322 and like this too.  I have 10x and reloader 7 to test yet.  I have a 16" DPMS ar15 1:9 twist.

I'm not sure why you would really need to more to a "faster" powder for a shorter barrel, but then again I am no expert.  My advise is to try the powders that others have had success with first.  Then if you don't get results move to something else.

Try these H335,  H322,  Reloader 15,  Varget,  BLC-2,  Reloader 7

My apologies...10.5" AR 1/7 twist LMT 62grn. steel core