Henry Ernest Dudeney/Puzzles and Curious Problems/322 - The New Gun/Solution

Puzzles and Curious Problems by Henry Ernest Dudeney: $322$

An inventor undertook that a new gun which he had manufactured, which when once loaded,

would fire fifteen shots at the rate of a shot a minute.

A series of tests were made, and the gun certainly fired fifteen shots in a quarter of an hour.

However, the Government refused to buy the gun, on the grounds that it did not do the job as advertised.

Why?

For the same reason they did not buy the gun in the puzzle published as $99$ - The Rejected Gun in Dudeney's $1926$ collection Modern Puzzles, of which this is a retread:

An inventor offered a new large gun to the committee appointed by our Government for the consideration of such things.

He declared that when once loaded it would fire sixty shots at the rate of a shot a minute.

The War Office put it to the test and found that it fired sixty shots an hour,

but declined it, "as it did not fulfil the promised condition."

"Absurd, said the inventor, "for you have shown that it clearly does all that we undertook it should do."

"Nothing of the sort," said the experts. "It has failed."

Now, can you explain this extraordinary mystery?

Was the inventor, or were the experts, right?