Here is my Jungle Carbine. I think they are the most attractive bolt action military rifle ever. This one is from ROF Fazakerley. Here are some of the differences from the No. 4 made to lighten them. The hole in the bolt handle is much larger and material has been removed below the sight. The sight 'only' goes up to 800 yards while the No. 4 goes up to 1200. My No. 4 is a Mk I* which means simplified war production. You can see one of the differences in the serrated bolt release catch on the No. 5 just to the rear of the back receiver ring. The No. 4 doesn't have the catch but instead has a very shallow grove in the right receiver rail just behind the bolt head. I think it is better and easier to use on the No. 4 and was surprised they didn't use it on the 5. Here is the No. 5 with the hand guard removed to show lightening flutes machined into the receiver. This is one of the best ways to check for modified No 4s being offered as real Jungle carbines. The stock, flash hider and butt pad are relatively easy to fake but the flutes are a a pretty involved operation unless you are doing a production run. I made the seller remove the hand guard to verify when I bought this one in 1991.