I've made paper cartridges for a handgun but none for rifles.I understand the paper doesn't need to be "nitrated" for long guns.They can be but don't really need it, but it's not a necessary step in other words, Is that true?
There is no need for rifle cartridges to be nitrated. The paper is dragged out by the bullet and discarded. Some went to extra trouble to ensure the paper did not burn and disintegrate in the barrel (eg Chassepot). Musket cartridges also had no need to be nitrated as the paper was put into the bore after the powder was poured into the barrel so sat upon it and was blown out. It was needed as both a wad to seal the bore and as a sabot to hold the ball. It is only when the paper remains may stay in the chamber that paper and gut cartridges need either nitrating or chemically converting to gun cellulose, commonly called gun cotton.
There were several ways to deal with paper cartridges. One was to attach the bullet to the powder case and have it dragged out. This leaves the base behind so that was dealt with by, for exampLe, storing the powder pressure behind the bolt and releasing it after the pressure in the barrel dropped once the bullet/powder case has been expelled. Another is to have a greased felt wad at the rear of the cartridge which remains, but is then pushed up the barrel by the next round being chambered. The greased wad being pushed out of the barrel by the bullet of the next round being fired, also cleaning and greasing the bore as it goes.
The common nitrated paper cartridges were the revolver ones where the gap between the chamber and bore makes other methods tricky. People often use old or reproduction rifles and complain of fouling in the chamber and often this can be traced to them failing to understand how the original worked and trying to use nitrated paper which must leave the remains as it is still paper. It is only the 'gun cotton' or ' flash paper' that can be entirely consumed and they have fragility and safety issues. Otherwise one is not trying to consume the paper but, on the contrary, to preserve its integrity as it travels up the bore attached to the bullet.
My personal experience is with the Westley Richards Monkey Tail and the Chassepot rifles. The Westley Richards seals the bore with the greased wad of the last round so the new round is safe from the remains of the rear of the preceding one. The Chassepot cartridge goes to much trouble with silk gauze wrapped around the powder case to keep it from burning up and be expelled whole and a rubber disk to contain chamber pressure behind the bolt to blow out the cartridge base once the bullet has left the barrel and the pressure drops. Both tie the powder case to the bullet. I understand, but have not used one, that the Sharps rifle went from paper case to a linen case to do the same thing. Many try to simplify the Chassepot cartridge, which is complicated, but I found that the closer I got to the original design the better it worked.
Apologies for over answering the question.