Defence corrispondent Telegraph 2002

"Earlier this month an MoD inspection team flew to Afghanistan amid reports of a number of stoppages affecting Royal Marine commandos hunting al-Qa'eda fighters.

The team, including two experts from Heckler and Koch, was horrified to find the problem was far worse than previously thought.

A demonstration by a company of Marines returning from a mission showed a third of the companies' rifles, between 30 and 40, not working properly.

The Marines were told to treat their return to Bagram by Chinook helicopter as a landing in a hostile environment. The whole exercise was filmed.

As the helicopters landed at Bagram, throwing up a huge dust cloud, the Marines poured out of the helicopters and ran to the firing range to fire their weapons.

Problems they encountered ranged from stoppages caused by dust in the rifle's working parts to magazines falling off. Even those who managed to fire their rifles had to work hard to get the safety catches off.

There was a stand-up row at a meeting in the MoD last week when a senior Army officer accused the Marines of causing the stoppages by not keeping their weapons clean.

Royal Marines officers dismissed the claim, saying that the modified weapon was too high-maintenance and they had been forced to clean it as often as five times a day.

One said: "If you're jumping out of a Chinook into that kind of heat and dust, it wouldn't matter how clean the rifle was beforehand. The minute you got off, it would be covered in shit."

Heckler and Koch experts identified five serious problems needing to be rectified:

The oil's ability to lubricate the weapon is breaking down in the high temperatures;
The impossibility of switching off the safety catch under fire;
Too much dust getting into the magazines, preventing them from putting rounds in the rifle chamber;
Too much dust getting into the rifle itself. Experts suggested a protective cover over the working parts;"

And these are military guns with large tollerences built for these kind of conditions, not custom built guns headspaced to 2/3 of a cunt hair and 2 lb triggers.
But of course as you pointed out I do not have enough personal knowledge in this field as I know fuck all about rifle design or function. I get all my knowledge from the internet.

Regards