what I found in the end was that the 10,75x52R rounds from collath 500 had a HWM headstamp. well this means "Harald Wolf Mastergunworks". send Harald Wolf an e-mail about itand here is his answer:He have never loaded ammunition in this caliber because the order stopped because of the death of the customer. the gemtleman from austria had have a beatyful double rifle from Springer's but actually made from Francotte in Liege.
there were made some hundred cases with correct headstamp that he sold two years ago on egun after laying around for 15 years. also some hundred softpoint bullets, made from Delsing in Germany after an original. harald found that Springer's dont have knowledge about the round and show now interest for the components or loaded ammunition.
the bullets for the 10,75x52r springer were very light for the diameter, 16,7 gramm flat( must be arround 265 grains) with a small hollow point.
original ammunition was made till into the 1920 years from Georg Roth and Hirtenberger in austria and maybe in czechoslovakia. he did not find anything about ballistic and service pressure.
this old austrian gentleman had made ammuntion for his double rifle from russian 7,62x54R ammo after WW 2.

this german gunmaker sells 10,75x52R dummy rounds, made from this component's
http://www.dekopatronen.de/html/weitere_patronen.html
they cost 12 euro each and I will at least order one for the collection. if someone here also have an interest,I have send small parts in a registered letter to canada for 3 euro iirc and can make this for you.