PF230176 barrels markings 2/52

Curious about some barrel markings

On top made in england in a semi-circle with a sideways I or 1 followed by ZZ, (no idea) and on the left side J8 (Inspector mark?).

Right side has F50 and broad arrow. (ost of the gun's parts are stamped F50, that im confident is made in Faz in 1950) feb 52 for final assembly.

Usual 18.5t proof mark left side at 9 oclock.

The sideways 1 then ZZ has me stumped, cant find any references for that...

Inverted Capital D inside a circle above and forward of the extractor screw, inspector marking?

if anyone could point me at some URLs please?

D in a circle indicates a method of machining where everything was taken from the thread as opposed to threading after machining. I know that there are some who are going to disagree and talk about draw lapping, Scottish Country dancing classes, needlework lessons at Fazakerley etc etc, but take it from me.............

Thanks, is the sideways 1 then ZZ an inspector stamp? Ive seen it on 3 guns now. One, one of the "infamous" irish blondes just out of grease wrapping so un-used. My gun and one other 1/2 FTR'd in 53, all seem pretty good barrel condition so I dont think its an armourer's stamp.