I tried several loads today in my 56UF No. 4 Mk 2 with CA 7.62 barrel:

DAC ‘59 Service Issue 7.62 NATO Ball - pulled bullets, dumped powder into measure, re-metered the charges at 39.0 gr thru my Redding measure.  Reseated the service 147 gr hard point BT bullets.  This ammo had a range of powder weights as loaded from 39.8 to 42.2 gr from 40 rounds.  

The results were much better than shooting the ammo “as loaded” and also better than the 150 gr SMKs subbed for the service bullet keeping the original powder charge.  

I was surprised how well these service bullets shot.  10 rounds, 200 yards off bench, 3.7 inch center to center (1.8 MOA).  Shots 9 and 10 scarred the edge of the X ring, a hair off a 100-9x score.  

Of the 40 rounds I shot with these pulled bullets and re-metered charges, there was 4 fliers in what would otherwise be sub 1.5 MOA groups.  This service ball ammo has very inconsistent powder charge weight causing vertical dispersion (as seen in the targets in the OP with both the service bullet and with the 150 SMK) and approx 1/10 fliers likely due to bullet quality.  Even still, for service ammo, groups were respectable.  

Conclusion

The No. 4 in 7.62 had a reputation for not being as accurate as the .303 on the target range.   My conclusion is  this was likely due to sub-standard quality/consistency of the loaded service ball ammo. 

I don’t know if the NATO accuracy standard for the 7.62 ball cartridge was less than the .303 standard, but I can say that for several .303 service loads I’ve tried, the .303 performed better than the 7.62.  Perhaps this was what the British NRA and Canada DCRA struggled with in the 1960s as they converted their .303’s to 7.62 for Service Rifle match shooting.  

Short Range Load

For something completely different, I tried this load:

Case - DAC 1962 Neck Sized

Primer - WLR

Powder - H4895, 42.0 gr

Bullet - 125 gr Speer TNT varmint

COL - 2.70 in.

200 yards, prone, 10 shots:

Shows how unsteady I was in prone today, walked it all around the outside of the X ring.  Group was 2.6 MOA. Nice light recoil and makes a good short range load or varmint load.