I think that that is where the courts in the U.S. and the U.K. will differ Muir.
No court in the land or for that matter Europe would reasonably expect an article such as a firearm costing so little to have a life of greater than for sake of argument say 10 years. You would almost certainly be required to demonstrate that during the life of the firearm that it had been maintained properly and inspected regularly by a competent gunsmith when pursing such a claim, something that few of us could do.
If as you suggested you continued to use the rifle knowing that it may be possibly faulty then the court would undoubtedly rule contributory negligence and dismiss the claim awarding costs to the other side.
P.S. Yes I know that many firearms continue to be used that are 100 years old or even older, but what would the courts consider a reasonable expectation of serviceable life taken into consideration with purchase price. Not even Judge Judy would pay out on that one.