ok..'messing' with hammer spring is now well advanced.
I've obtained an original CF FAL hammer spring which is ~8mm longer than the .22lr one though the wire guage is identical. I've trimmed that 5mm below that of the .22lr hammer spring and the gun now cycles subsonics with a fair degree of reliability.
I emptied a box of 50 remington subs with no jams
50 RWS subs generated 3 'short strokes where the empty case was ejected afresh one chamberd but the hammer wasnt cocked. the gtouping was improved to less than a 10p peice at 25yds on rapid fire.
50 eley match grouped inside a 5p peice at 25yds with no failures to chamber or cycle the hammer but a couple of failed case ejects (nipped in behind the breech block and jammed the hammer).
the Winchester subs did the best overall with no failures and a nice consistent group
I'll continue trialing with a few more boxes and make sure its sorted.
Most importantly ...no light strikes in evidence
Looking promising
next job is to remove the flash hider and fit the SAK mod to see how quiet it is.
That Flash hider is on bloody tight! got the right size spanner on it and not a hint of thinking about moving