Perhaps so, but that doesn't change that two 20pdr Parrotts still blew their muzzles off at Antietam, which is 9% of those engaged being permanently damaged. I'll accept that I cannot find stats for the 10pdr that indicate a similar unreliability, but you did claim that even the 20pdr didn't show that pattern.
I've seen mention of a NYT article to the effect that the Parrott was dangerous in drill, and in addition:
Major General Quincy A. Gilmore, U.S. Army, respected them. He reported: “There is, perhaps, no better system of rifled cannon than Parrotts; certainly none more simple in construction, more easily understood, or that can with more safety be placed in the hands of inexperienced men for use. The enormous and constant demand under which it has been rapidly developed, particularly among the larger calibers, to its present state of efficiency and excellence, gives promise of a degree of perfection that will leave little to be desired at no distant future.” Gilmore also recognized that the Parrotts had defects, particularly “their very unequal endurance.” Some burst in their early stages of use; others fired thousands of rounds before they became unusable.
Cole, Philip. Civil War Artillery at Gettysburg (p. 107). Colecraft Industries. Kindle Edition.
Other artillery commanders begged to be rid of the Parrotts. “I would most respectfully recommend that the 20-pounders be taken from the Macon Light Artillery, as it is a good company and deserves better than to have its members wounded and killed by defective guns,” advised Confederate Major John Haskell. E. P. Alexander once complained, “The 10-pounder Parrotts in my command I have condemned entirely, and have made arrangements with the Ordnance Department to exchange them all for 24-pounder howitzers, having found it impossible to get satisfactory firing from them, and I hope to be rid of every one when we take the field.”
Cole, Philip. Civil War Artillery at Gettysburg (pp. 107-108). Colecraft Industries. Kindle Edition.
Similarly, on this site:
https://www.civilwarhome.com/artillery.html
On the 2.9" and 3" Parrott:
The real difficulty was the gun's unpredictability. Some Parrotts served long and dependably, firing several thousand rounds with no problem. But cast iron cannon tended not to show wear and tear. The metal simply gave way whenever it gave way, after few rounds or many, so there always was a high level of uncertainty in connection with the use of cast iron guns.
Private Augustus Buell of Battery B, 4th U.S. Artillery (a Napoleon battery) later noted, perhaps with some sarcasm, that "so long as the Parrott gun held together it was as good as any muzzleloading rifle." (Buell, p. 22)
Unfortunately for the crews who worked them, Parrotts too often failed to hold together and became extremely unpopular with artillerymen. Buell himself best expressed the common view when he later said, "If anything could justify desertion by a cannoneer, it would be an assignment to a Parrott battery." (Buell, p. 147)
This seems to indicate that there is a general sense of unreliability in the Parrott, including the field gun calibres.
I'm not sure I follow. The point I was making is that the Krupp C/64 was definitely not a 100% reliable gun, in that it
did have a rate of failure (in the breech, and in premature detonation of shells) that was exclusive of drill problems. Nevertheless, they sufficed to defeat the French.
That the British dumped the 12 pounder Armstrong may simply indicate the British holding their arms to a higher standard in peacetime than these other powers in wartime; in wartime, the British would use the 12 pounder Armstrong.