So the royal small arms 1916 has a broad arrow on the left side of the barrel in that area, do you know what that might mean in terms of who used it?
Horizontal arrow, British.
Vertical arrow, New Zealand.
Starter pack guide to Enfield markings:
https://www.milsurps.com/enfield.php?pg=gh7.htm
https://www.milsurps.com/enfield.php?pg=gh10.htm
https://www.milsurps.com/enfield.php?pg=gh11.htm
https://www.milsurps.com/enfield.php?pg=gh12.htm
Past that, things can get pretty esoteric. The Lee Enfield pattern rifles had a very long service life, and the individual guns themselves had a habit of "travelling" between different armies, gaining stamps (or getting over-stamped) along the way.
I have a No 1 Mk III that was made in England in 1917, got the British broad arrow on the receiver, and then after the war must have been sold to Canada (best I can guess), where it got the rifling shot out of it in training between the two wars, because the barrel itself has a C broad arrow (Canadian acceptance stamp), and a Longbranch Arsenal marking.
It's a whole weird thing, because Longbranch only got stood up at the beginning of WWII, by which time the Canadian army had moved on to No. 4 Mk I pattern rifles. But at the very beginning, the Canadian army was desperate for as many "sticks that go bang" as they could get, so some number (several thousand, no one really knows, the documentation is lacking) No. 1 Mk III rifles were re-barrelled and pressed into service. Most of those ended up with "Home Guard" type units, or POW Guards (lots of POW camps scattered around Canada during the war).
It's a fun game to play, look at all the stamps on an old surplus rifle, and ponder on "the stories this rifle could tell" - but you never really know for sure.