Thank you JPE JB and Jim C for your responses. I will check and try all things mentioned. The heads I use are triple swaged .357 by a private person, and in another revolver I have, produce sub inch groups all cloverleafing to one hole - 10 rounds - shot standing unsupported. I take from that it's not me or the ammo at fault.
The throat to cylinder is 3 thou and very even. The forcing cone is a precise 11 degree as is the crowned muzzle end. The crowning was hand finished. Aristocrat rib not loose. Forcing cone cleaned of any lead using both choir boys and girls (LOL!)
I'm in the process of making up some .356 and .355 to test out on Friday.
If it still shoots rubbish then the barrel is coming off in favour of a bit of DONNELLY .357 8 groove 1 in 14 I've had hanging round for years.