Interesting, I'd have thought it would be easier to use an original patent breech design. I have an as-new PH P1853 3-band en-route, will check it out when I get it. Do you see the seam for the sleeved area around the nipple boss? Or is it polished to a near-invisible line?
Either way, if fitted well, it should be just as strong - probably stronger as they used steel vice iron.
As for the PH tale, you can still buy new PH Enfields, but they are now made in Italy for Navy Arms using the PH gauge set. The fit and finish is not as nice as when PH made the guns in Birmingham before 1990.
The late Herd Woodend loaned the P1853, 4th model master gauge set to Parker Hale and they produced a slave set of gauges with which to build their replica. The original set was returned to Enfield Lock in 1978.
A lot of American re-enactors have a love/hate relationship with the PH reproductions, mainly because they reproduced a regulation War Department 4th model, which was never used in the American Civil War. The ACW guns were London Armory Co. and Birmingham sub-contractor-produced 3rd models. Unlike the 4th model Enfield, there was no parts interchangeability an each gone was hand-fitted. The barrel bands and lock plate designs were different, along with the lock plate nail escutcheons.
Interestingly, the 4th model P1853 was barely used by the British forces either. Most sat in stores until they were converted some years later to Snider-Enfields.
The story that they used RSAF Enfield tooling is just myth. That tooling was long gone by the 1970's. They did use the same gauges, which means PH muskets interchange parts with original 4th models and most snider-Enfields as well. They are also the only copy I know of with progressive-depth rifling like the originals.