New to me RSAF 1918 No1 MK III*

[JerryEAL]

Check the safety spring also. Mine was out a little and the bolt was very fussy as to whether it would open or not. The safety would move ever so slightly after firing and I had no idea what it was. Changed the spring that solved it for me.

[musketjon]

. I have never seen any of my other gun's muzzles look quite like this, so I was confused if it was worn or something.

That's because your other barrels have 4 grooves instead of 5.
Jon