If we see now a days parade films from marching WW2 armies, we see perfectly folded tent sheeds around and over the blanket rolls.
When there weren't cameras, they carried the folded tent sheed-ponchos under the main flap, because it is easier to get it out and use it as a poncho if it starts raining.
It is possible to use a nice looking woolen blanket, that is light and thin, and fold in it a sleeping bag:
You put the sleeping bag parallel on the blanket.
After you put the hood of the sleeping bag into the bag, you fold the foot part of the sleeping bag once, to shorten the sleeping bag to 3x45 cm= 135cm, that is three times the length between your elbow and the end of your fingers.
You fold both blanket sides over the ends of the sleeping bag, perfectly parallel edges are necessary. The sleeping bag fills that "pockets" nicely.
In the end both sides of the sleeping bag are the ends of the horse shoe, you want to form.
The third side you fold over too, round about 20 cm, creating a pocket of the length of the horse shoe. And than, beginning at the fourth side you roll as tight as possible the blanket with the sleeping bag into this pocket, and form immediately the horse shoe , the edge of the pocket belongs at the middle part at 2/3 of the roll and to the upper, outer direction, pointing in the end to the person with the open edge when attached to the rucksack.
Holding it tight with hands and knees, you immediatly attach at first the both lower ends of the horse shoe to the rucksack. Than you attach it (exactly!) in the middle upper point at the flap of the rucksack.
The first result will not convince you.
Perhaps the roll is to long or to short, perhaps not tight enough.
After 20 or 30 trials you got it and if you try to remember, what you did to get that convincing result, you will be able to manage it the next time in the first run.
Every 12 years old german boy scout can do that. YOU can learn it too!
That's a pretty good equipment, because you use the modern sleeping bag but give the old school image, and the woolen blanket protects the light but sensible sleeping bag against sparks if we sleep under a lean to shelter next to the fire.
The secret of this horse shoe roll is that you don't form a triangle, it is a square !!!
If you got a triangle your roll is to short.
135cm is the right distance to start with to learn it. But each rucksack of course requests a different length of the roll, perhaps 150cm, perhaps 125.
Don't count in cm, just remember (3 times) the length from your elbow to a point of your Hand! That's your personal measure, you have with you.
Good luck to everybody!
If you all trained it well, I'll send you a prussian Lieutenant to examine you!
;0)