I think you meant 178 grain not 198 grain (typo). The Hornady loading manual is pretty conservative. I have used Alliant Power Pro 2000-MR with the 178 Horn Match ammo in my M24R to get the velocity I want for 800 and 1000 yard shots at Quantico, but the COAL = 2.880" (so its a single load round).
The Alliant Powder manual with 175 SMK max is 47.7C (compressed) with a velocity of 2760. The 178 gr should be downloaded a little bit relative to 175 SMK, but regardless I think that load data is probably too hot
at magazine length, but its worth experimenting with 45.0 to 47.0 (max
) grains in a ladder test of your rifle - just load it a bit long (2.85"+). I got 2763 fps with 47.4 in a Lapua case with Fed GMM primer at 2.880. (ES =31, SD =13). In fact I shot a respectable 183-2x (out of 200 possible points) at 800 yards last April with my M24R, but I think some fine tuning of the load is still in order. Here's a short clip at 800 yds that day.
http://vid289.photobucket.com/album...ntico April 2016/MOV_6537.MOV_zpseyh7faqp.mp4
...good luck and let us know if you find a magic recipe...but I recall the ES and SD with 47.0 grains was impressive with the 178gr bullet (single digit SD of 8 I think). 46.0 grains of PP-2000-MR should get you to 2600+ fps. I still haven't seen pressure signs with this load up to 47.4 at 2.880", but work up slowly - as it has lots of mojo...
Warning: I don't know the overall length of the 178 ELD/ELD-X bullet, but presumably its longer
than the 178 BTHP match bullet that I used - so please download from what I stated as I suspect you are using a longer bullet that will displace more internal case capacity, even if its the same weight. Maybe start at 44.0 to 45.0 and slowly work up in 0.2 increments of 3 rds each to see what groups well. Also, I was not using CCI #34 primers with this load, which are mil-spec primers and are basically magnum primers, so don't use this data with that primer(!) I used Fed GMM primers.