If your only getting 2400fps from a 20'' my 18'' will be a lot slower, I'm getting 2450fps ave with 120gn ELDM"s Shooter World Match Rifle, with 29.4gns, and getting just under 2400fps with 123gn ELDM's with A2520, with 29.4gns and low 2420's with SWMR my next trip to the range I plan to run the A2520 @29.6gns to see how it preforms, these loads were shot with 120gn ELDM"s 123gn ELDM's and shot 1.5'' groups @100yds, tho not super impressive groups at 100yds yet, but I plan to tweak my seating and crimp on my bullets to see if I can improve upon my group size, but IMO for a gas gun {AR} that's not bad groups at all JMO and my barrels are still not copper fouled or seasoned quite yet, The reason I asked about the H335 is I have about 6lbs of it and have not tried this powder at all out of anything, I originally purchased this powder for my 5.56 AR's Thought it might work in the Grendel, I have also been reading some info about RL15 powder being comparable to SWMR powder? anybody got any info on that? if so what are you loading in the Grendel? I know velocity is not everything, but I would like to over 2400fps from my 18'' barrel with decent accuracy! 