I had a P17 sporterised by BSA as my hunting rifle for several years. Had the orig 19something barrel too. Rough as a sidewalk and fouled till the barrel was green. Pretty sure it was a 10 twist but it will not matter as any desired bullet will work.
SHOT SUPERBLY.
Was an honest 1/2 min rifle (3rds) and I really enjoyed plinking with it out to 1000m. Groups would grow if the barrel got hot but I am pretty sure, that will be the norm. If you can rebarrel, it will be a great shooter.
I used molied 165gr SST's over H4350, CCI BR2 primers in LC69 brass (took a bit more prep but worked really well). Would use Win brass these days.
I tuned the trigger to be a single stage with a crisp let off (not sure you can do that for service rifle). Bedded the action. Really needed that. Put in pillars. Swapped in a #### on opening kit (positive that will not fly in service rifle).
I have a really warm spot for the Lee Enfield No4's but I think the P's offer much more for the match shooter.
Jerry