My Parker-Hale .451cal Whitworth rifle, serial #888, from 1986, had the reduced-volume so-called patent breech.
The gauges used by Parker-Hale to make their reproduction rifles were borrowed on long-term loan from what was then called the Ministry of Defence Pattern Room. Initially located at Enfeld Lock, it removed to Nottingham when all Enfiled production ceased in the late 1980s, and under the care of BAe, occupied a new building in Nottingham. The curator, all this time, was the much-missed and dearly-loved Herbie Woodend MBE, a man I was very proud to call a close friend. I took a bunch of students there one day, and the gauges had just arrived back from P-H, after a long and involved battle to get them back. While the studes were oohing and aahing, Herbie and I uncrated them and counted them all back against the original manifest of the sealed pattern, made in 1853.
They were all there.
The Pattern 53 rifled musket did not have a patent breech, but did have a one-piece screwed-in breech plug. Anything that differs from that, apart from the various models of .451cal rifle which DID incorporate the patent breech - the two and three-band Volunteer and the Whitworth, is not based on the sealed pattern, but is likely an exigency of modern manufacturing.
tac