Feinwerkbau 300 S (German side lever)
Just back from a service by Feinwerkbau
The 300S is a recoilless match rifle which took the 10 meter world by storm, back in the 80s. The whole barrel/piston section is set on hardened steel rails which allow it to travel backwards during the firing cycle.
Accuracy is rated at 0.040 of an inch!!