Depending on how much under 20" we are going with the 175gr bullet, you may want to spell out exactly how long since things start to change when you get way down below 14".
I would suggest staying away from this and 2000MR. These powders are slow and the muzzle report and flash are excessive in a 20” barrel.
Just fwiw, at 20" you are getting a nearly identical percentage of powder burnt with 42 grains of 4064 and 47 grains of cfe223, with a 168 smk. It's within 1%.
True, but the biggest problem is that they seem to have abandoned doing service rifle loads some years ago because they haven't added a powder to it in forever.
CFE is a weird powder. I think it was designed for shorter barrels in 223 and 308. It has its issues, like temp stability, and it may be a bit more blasty than some, but it can give you back all of the velocity you give up with going to a shorter barrel. I've always shot it with a can, so I don't really know if it gets crazy bad, but I see it as a way to change the compromise you are making in shortening barrel length.
To that point you do pick up a fair amount of velocity with 2000MR. As I recall I was getting on the order of 100 fps but I wasn’t look for additional velocity.
I tried CFE 223 under 150fmj, 168eldm and 175 smk with federal 210 primers. I could never get it to group well. Looking down the bore after a few shots it seemed to leave small flakes of what I presume is unburt powder. Somthing I never saw with stick powders. On the plus side it meters very easy in a powder thrower, wish I could get it figured out.
