223 with 7 twist

80 grain Nosler Custom Competition shot the best 10-shot group I've posted. If you are going to shoot long strings, like F/TR, use one of the Hodgdon Extreme powders (H4198, H322, Benchmark, H4895, Varget), IMR 4166, or IMR 4064. IMR 4166 is supposed to produce less copper fouling, which still happens even with coated bullets.
 
I have enjoyed some good results at 300yds with 69gr SMks in a NM AR (cleaned the prone rapid more than a couple times). My best results were with 25.0-25.2gr Varget (about 2800fps) in a LC case.

In my MK12 (18" Rainier Ultramatch 1:8") I run 23.5gr of 8208XBR behind a 75gr Hornady BTHP, which is good for 2750fps out of the 18" tube with the can on. If you're not mag-length limited, TMKs and ELDMs are worth a look.
 
I have enjoyed some good results at 300yds with 69gr SMks in a NM AR (cleaned the prone rapid more than a couple times). My best results were with 25.0-25.2gr Varget (about 2800fps) in a LC case.

In my MK12 (18" Rainier Ultramatch 1:8") I run 23.5gr of 8208XBR behind a 75gr Hornady BTHP, which is good for 2750fps out of the 18" tube with the can on. If you're not mag-length limited, TMKs and ELDMs are worth a look.

How does the Mk 12 shoot compared to the NM? I'm guessing it's a 20" WOA upper?
 
It was a very early White Oak Precision 1:6.5" 3-groove PacNor upper I was shooting in the 99-04 timeframe. Long range (even 1000) was shot using 90gr JLKs over 23gr (? old memory) of 4895. Not even sure WOA existed when I had John build that rifle. I have since sold it so no direct comparison and 2 very different rifles but with similar accuracy capabilities. I never put optics on the NM rifle but shot it for groups from a sling and sandbag prone. The MK12 has the NF 2.5-10x24 and I have grouped it from both bipod and bag.