A Heerenbüchse is a very peculiar and slightly quaint-appearing gun (readers take notice of the also peculiar spelling, such as in the original query, for the inventor's family name was Heeren, adding later nobility titles; hence not a "Herrenbüchse" a.k.a. gentleman's rifle, although many happy buyers subsequently feel so promoted... ;-) ).
Humorous shooters might call it "an over-engineered reverse lever-action with falling block". Apart from Nagel & Menz in the Grand Duchy of Badenia as the original rights holders, the guns were later frequently made in Ferlach by various gunsmiths, at rather corresponding prices.
The cartridge, namely the 6,5x57 R as the rimmed sister of the 6,5x57 Mauser, but with a slightly too low CIP-set max pressure limit (!), is extensively treated in the venerable "Blue Bible" reloading handbook of RWS, last in its 9th edition 2002, which is also online accessible. The RWS propellants may however have changed somewhat in the meantime, and many German reloaders now anyhow prefer the Swiss RS powder.
The guns were never ever intended for black power, and the twist rate and groove depth might not be exactly conducive to the use of lead bullets.
A copper-clad (galvanized) or high gascheck lead bullet ("Kupferschuh") would be mandatory for any experiments, I surmise.
(1) The nitro cartridges initially had a 10 grams jacketed bullet weight,
(2) and lateron a light 6,0 grams SP was offered, with a straighter trajectory for wider mountain (or plains) shots on smaller cloven-hoof game, notably on chamois, and also for roe deer. As a comparison, the 6,5x57 (R) was used in Germany for hunting situations where the French used the 7x54 MAS-Fournier, and US-Americans the .25-06.
(3) Lateron, the sometime added 8,2 grams H-Mantel claimed a middle position between these two bullet weights.
Regards,
Carcano
