Leaving the 6.8...

[LRRPF52]

As someone who has both I would go 18”. My 16” 6.8 is faster than my 18” Grendel when loaded to safe pressures.

What loads and speed are we talking about, and what does that look like at 75yds, 100yds, 150yds, and 200yds?

Every time I’ve run the numbers, the Grendel starting slower will catch up and overtake the 6.8 within pretty close range.

Hornady’s data for the 16” 6.8 SPC with 120gr SST is 2460fps with an inflated BC of .400 G1.

Hornady’s data for the 16” 6.8 SPC with 110gr V-MAX is 2550fps with a BC of .370 G1.

My data for my first 16” AA barrel build with 123gr A-MAX and SST is 2439fps with a Litz BC of .462 G1 (not Hornady’s inflated BC of .510).

You can load the 6.8 SPC faster than that. I can load the Grendel faster than that.

6.5 Grendel with 123gr SST at 2439fps G1 .462 standard atmospherics

50 2347fps 1505ft-lbs
75 2302fps 1448ft-lbs
100 2258fps 1392ft-lbs
150 2170fps 1286ft-lbs
200 2084fps 1187ft-lbs 3.6” wind drift for 10mph full value (hunting vital zone consideration)
etc. It still is supersonic past 900yds.

6.8 SPC 120gr SST .400 G1 BC at 2460fps same conditions
50 2354fps 1476ft-lbs
75 2302fps 1412ft-lbs
100 2250fps 1349ft-lbs
150 2149fps 1231ft-lbs
200 2051fps 1121ft-lbs 4.1” drift 10mph wind full value

With hand loads, I’ve seen guys load the 16” 6.8 SPC chamber with longer freebore into the high 2400-low-2500fps range from 16” barrels.

I can load a 16” Grendel to 2500fps with CFE223 or LVR and still not exceed MAP. Or I can just find my accuracy node and not even worry about pushing pressure because the bullet is going to retain a lot of velocity on its own, no matter what speed I spit it at.

That all said, because of the current ammo climate, I’m actually considering getting a 12.5” 6.8 since one of my local Sportsman’s Warehouses stocks the 200rd cases of Hornady AG and nobody seems to be buying them, or they just happen to be on the shelves whenever I go there every time.