Here is a resume i wrote some time ago to adress the confusion about chamber length:
Danish Rolling Blocks and chamber length confusion
The original Danish RB round was 11.4x41.5R rimfire. Load was 52grains in 1867 and changed to 60 grains of BP behind a 385 grains boolit.
Denmark ordered 20000 rifles from Remington to be delivered within 6 months. That backfired for Remington because Sheffield could not deliver enough barrels.
The Danes got to make their own RB’s without paying royalty as a result.
5 production lines was set up and each of them had a master gunsmith which was in charge of quality. Each smith had to manufacture his own set of Go-No Go gauges and have them certified by the factories master controller. This becomes important later!
All is well and from 1867 to 1878 @78500 RB’s are manufactured.
In 1884 the Danes start to develop a replacement for the RB and at the same time they start to ponder a way to modernise the RB’s. In 1896 they were officially converted to: Smokeless, centerfire and jacketed bullets.
And now comes problems in heaps falling on the arsenal, Because of the 5 different Go-No Go tools it is clear that bores range from 11.25mm~.443” to 11.75mm~.463”. You can’t design a standard round with jacketed and smokeless that will work within those ranges with any kind of accuracy and without huge variations in pressure. So a LARGE long throat is devised to size the bullets for the smaller bores.
That is why some Danes will chamber a 45-90 without problems and why the 11.4x56R thought exists.
In the development of the final cartridge choices in smokeless was dismal and experiments led to the 56mm cartridge. But that meant grinding down the hammer for chamber access and that was dismissed along with slower reloading of the rifle. Only 100 rifles were ever converted and they can be easily identified by the ground down hammer. Most/all were scrapped so the likelihood of hundreds of them popping up in the US is nill. You have a ”standard” 11.4x51R chamber.