IMR 4198 with 52/53 SMK I find to be exceptionally accurate. I just think it is a pain in the butt as it is an extruded stick powder.
I have tested the below and found it to be more accurate than me.
Quote from Ed Harris, I have found this basic article to be a fountain of good loads. (Ed's Red) fame....
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Best all-around accurate load I have found, regardless of rifle type or
barrel twist is to use the Sierra 52-gr. or 53-gr. benchrest bullets
and 22 grs. of H4198 or IMR4198; or alternately 23.5 grs. of H322, and
anybody's match primer, in whatever brass you have, but sorted by make
or arsenal and year. This is not a high velocity load, about 2950 fps
in the AR-15, but HIGHLY accurate. Shoots well in 7" twist or 12" twist
barrels. This load was recommended to me by Wally Hart when I started
shooting benchrest and I have concluded that if a .223 rifle will not
group with this load, it will not group with ANYTHING! In a full
blown benchrest rifle, taking GI cases assembled on a Dillon loader,
with no benchrest tricks whatever, the stuff averaged 1.39" for
twenty-five consecutive 10-shot groups at 200 meters fired the same
day, running a round-robin on five different makes of primers. Primer
make made no difference either! Likes CCI450 and Federal 205 best, but
Winchester WSR is also very good if priced compettively. DO NOT exceed
this charge with 4198, as this is a fairly fast burning powder for this
case. As for the H322, this surplus powder varies from batch to batch,
and while the 23.5 gr. charge suggested to me was a mild load with the
lot I used, others may run faster, so please be careful.
