My Howa 1500 was finicky with CFEBLK as well.
Nothing like you write about though.
I'm using Hornaday cases
I load mine with three different bullets. Two are .310 and one is .312 diameter.
The .310 diameter bullets are 130 grain spire point, flat base,fmj made for the SKS bores
The 123 grain SST also has .310 diameter
The 150 grain has a .312 diameter, spire point, flat base, soft nose.
These are my loads, loaded as long as the magazine will allow.
130grain fmj over 31.0 CFEBLK, over CCI250 primers = 2600fps. This was the best load for this bullet, around 1.5 moa with the odd unexplained flyer
150grain soft nose over 25.7 CFE BLK, over CCI250 primers = 2200fps. This was the best load for this bullet at slightly over 1moa, no flyers that weren't my fault.
I was hoping for better so went with REL7
123 SST over 30.0 REL7, over CCI250 primers = 2570fps. This load was the most accurate of all. 20 rounds into just under 1 moa at 100yds.
150 .312 flat base soft nose over 25.5 REL7, over CCI250 primers = 2400fps. This load put 20 rounds into 1.5moa at 100yds.
Also tried the 123, .310 diameter SST bullet over 28.5 AA1680, over CCI250 primers =2600fps. This load put 20 rounds into 2.1moa at 100yds.
The Howa action is very strong. You can load the 7.62x39 to higher pressures than you can for the SKS.
All of my loads listed are well over the maximum listed in most manuals for rifles such as the SKS.
I'm not going to recommend that you use them for your rifle.
They are safe in my rifle, without any visible pressure signs. Work up your own loads carefully as I did to get these.
I did try some .308 diameter 125 grain Speer flat base, soft point bullets in my rifle and accuracy was not acceptable, but not as bad as you indicate.