A Chinese high-speed train set another world speed record during a test run Friday, breaking its own record set just two months ago. The Chinese Ministry of Railways calls the feat “a major achievement of China’s technology innovation,” but doubts linger over just how much of China’s bullet-train technology can be described as its own.

This new world record was accomplished during the test run for a train called the CRH380A. According to a report by state-owned Xinhua News Agency, the train hit a topspeed of 486.1 kilometers, or 302 miles, per hour on the tracks between Zaozhuang City of Shandong Province and Bengbu City in eastern Anhui Province, part of a new high-speed rail line that will eventually link Beijing and Shanghai.

The previous record was set in late September when another CRH380A train achieved a top speed of 416.6 kilometers per hour during a test run between Shanghai and Hangzhou, capital city of east China’s Zhejiang Province.

“It not only marks a milestone in the construction of the Beijing-Shanghai high-speed railway, but also is a major achievement of China’s technology innovation,” Wang Yongping, spokesman of the Ministry of Railways, was quoted by Xinhua as saying.

Foreign high-speed train producers who taught China how to make bullet trains disagree. Most executives at those companies shy away from commenting on China’s high-speed technology out of fear of offending the country’s government, but a few who are willing to talk say that while China has succeeded in making the bullet trains go faster, the fundamental technology behind those trains remains more or less identical to the technology foreign companies provided originally half a decade ago.

“What China has is the same trains with beefed-up propulsion and other tweaked systems” to achieve faster speeds, an official from one foreign high-speed rail company says. “Fundamentally China has made little to no big technological advancements.”

It also makes little sense to go at speeds above 400 kilometers an hour if you consider the physics of high-speed trains, the same executive argues. At those speeds, he says, there is so much wheel slippage, and the energy requirements are so high, that “it makes no operational sense.”

Above 400km, he adds, the wheels and brake systems absorb so much strain that they need to be inspected more frequently for hairline cracks and other damage, which makes cost of operation punishing high.

Given all this, it should come as no surprise that the Ministry of Railways is expected to limit the Beijing-Shanghai trains to 380 kilometers an hour once the line is complete.