In my earlier writings about working with the 5.6x61R I did mention having fired factory ammo from a real rifle over a chronograph. This was post -war ammo (during the Walter Gehmann period) and was not nearly as fast as the advertised velocity. I don't believe the 3.2 grams "Special Pulver" load was R5, I don't know what it was, but when R5 was ever used I never noticed a reluctance to say it was R5. I only sacrificed one round of this ammo to the chronograph, so whatever the lower velocity was, it would not be enough data to consider it the average velocity. At the same time, I had ammo loaded by my friend and mentor Gene Enterkin with 4350, which was also a slow powder. These velocities with the 70 grain (High Power) bullet were over 3200 fps but did not group at all. In order to be able to show my friend a decent group fired with his rifle, I knew I had to reduce the velocity to match the capability of the bullet. Being aware of the warnings against reducing slow powder loads (specifically 4831) I elected to use my standby IMR 4895. I got groups good enough to show Gene on his Hospice bed, at about 3000 fps with the 4895. Now, the reason for this dissertation. Raimey mentioned using VV140 in place of the powder he thought was R5 as Axel says it and VV140 have similar burning rates. Instead of VV140, I use 4895 to replace R5 as I believe it too has a burning rate similar to R5. Based on this, there is nothing wrong with using either VV140 or 4895 normal handloading cautions are used. If harder bullets are used, going back to the slower powders would be called for in full loads.
There was an earlier question about the comparison of 5.6x57 to 5.6x61 vom Hofe. With the vom Hofe, the limiting factor seems to be the bullet diameter where bullet limitations preclude higher velocity. The limitation with the RWS seems to be the rifling twist rate is 1 turn in 10 inches. This works fine with longer barrels as normal and the 74grain Kegelspitz bullet of the factory load. Bullets longer than the KS or short barrels that lessen the velocity seem to affect accuracy. The 5.6x57 bullet is .224" which is the current standard and is available with very good bullets, but instead of being too soft may be too long. In my own 5.6x57, I intend to use the factory KS bullet and use 60 grain Nosler Partition bullet in hunting handloads.
Mike