IMR4064 vs. RL15

[crookedshot13]

Hello,
I would like to hear the 308 loaders thoughts on these two powders.

I'm using:
Rem 700 AAC SD 20" 1:10 twist
30F to 35F around -500 to -800 density altitude
155gr NoslerCC, 168gr NoslerCC, 175SMK
FGMM Brass
CCI BR2

Every powder charge was weighed carefully before the bullet was seated. (All at 2.800)

From what I understand, RL15 is supposed to work well with the heavier bullets, but I've seen the opposite.
46.5gr RL15, 155NCC was at 2705 fps, ES < 20 STD < 10
44ish (don't have my book handy) RL15 168NCC was at 2520 fps, ES < 20 STD < 10
43ish RL15 175SMK was at 2300 fps, ES > 100 STD > 50

But with:
43gr IMR4064, 175SMK was at 2540 fps, ES < 15 STD ~ 9

I want to hop on the RL15 wagon but my numbers are telling me not to.

What are the differences with these powders where this could have happened?

Do you 308 guys use RL15 for your 155/168 loads? What kind of velocities are you shooting for with a 20" tube and these bullets?

Any feedback is greatly appreciated.
Thanks

 

[Boomholzer]

It's your machine.
"43ish RL15 175SMK was at 2300 fps" and 2.80 for a SMK in FGMM smells wrong.
Rem 700 AAC SD 20" 1:10 twist
"43gr IMR4064, 175SMK was at 2540 fps" no doubt

Looking back through the book, anything "43ish" in factory Rem (per chamber and 175s or 178s) and FGMM brass was pushing >2500fps in a 20". Allot of data @ 2600fps in a Rem 22" per 43.0gr of RL15, in FGMM.

RL15 is a option, and a greedy one. To hear of a MV complaint in a 20" tube is kind of new to me.

 

[m1match]

Something isn't right, most likely with your chronograph. My 308 load for over a decade was 42.2 gr of 4064, cci BR 2, and 175 SMKs in Lake City 94 Match cases which gave me about 2620 FPS in a 24" Rock barrel. When I ran out of 4064 and had lots of rl15 for my 223 loads, I did some load development and ended up with 42.0 gr of RL15 with the same cases, primers, and bullets which yielded 2600 FPS in the same 24" Rock barrel. 2300 FPS is too low