Dilligaf I don't want to discourage you with your Mk2, I purchased an "Irish Contract" ROF/F 1/54 a few years ago and I'll share with you my first experience at 50yds with FMJ 174gr handloads, loaded to MkVIIspec velocity and producing 2520 at 15 feet in my No4. I wanted to know I would be on paper, I used a standard sheet of paper with a 2" square orange aiming point placed on top of the front sight.
My son was spotting for me with only my 10X42 binocs at the time, didn't bring the Spotting Scope .....and he called the first round.
I fired again. He couldn't see it.
I fired again. He couldn't see it. WTF!!! A Buckshot pattern FFS!!! Did I get .308" FMJ's mixed up for .3105"???
On examination of the target before wasting one more precious round, I discovered a keyhole, so I was right they are all over the pace ,...hmmmmm...
Looked more closely at the target and saw not a keyhole but all three making one enlarged hole. Whoopeeee.....
Those POF rifles were made on the same tooling as the ROF Fazakerly I'm sure you know that, and they should be able to shoot. Maybe a complete going over of the stock set up is in order. I fired from a bench rest as well with butt bag added and of course using the smaller aperture as you did. Maybe adding a butt bag to your set-up, buying some S&B FMJ rounds, which shoot nicely in mine, and practising the target let off for the No4 trigger.
Don't get discouraged early on, I never saw an Enfield that wouldn't shoot. A co-worker took his old sportered 1917 BSA, matching with CBroad Arrows out with us last time to the range, and it was all over the place. When I was finished with my AR I took it to my bench, took out two S&B FMJ's I had in my ammo box and fired both at 100 yards. They printed about 1.5" from each other, I showed him and then realized he was mixing up every weight and type round he had left over for years!!!!
I had a downloaded version of an Aussies book on setting up the Enfield for accuracy and it is worth reading. I had to reformat my drive and lost it and don't remember his name right off. I'd say settle down on a good bench rest and get used to the trigger let off first, before any working on the stock set..