討論:MK-108航空機炮
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Normally, gas-operated or delayed-blowback mechanisms are used in automatic weapons of rifle-calibre and larger because the chamber pressure in such weapons would be very high. Therefore, if a simple blowback system (where there is no positive lock between the bolt and barrel) is used, the bolt may recoil and open the breech while the chamber pressure is still high, causing damage to the weapon and split cases (see blowback article for more information). To avoid this, simple blowback guns have to use low-powered cartridges or a very heavy bolt.
In an APIB gun such as the MK 108, this problem was mitigated by using a chamber longer than necessary to hold the cartridge case. When the trigger was released, the bolt was moved forward by a powerful spring. It not only chambered the cartridge but kept pushing it forward, following the case a small distance into the chamber. Cases with a rebated rim were used, so that the extractor claw could hook over the rim and still fit within the chamber. Primer ignition was timed so that the bolt was still moving forward when the propellant ignited. The expanding gases from the fired round then had to stop the bolt, reverse its motion, and expel the bolt again from the rear end of the chamber. Before this happened, most of the gases had escaped via the barrel, dropping the chamber pressure to a safe level. The heavy bolt then continued to move backwards into buffer springs, which pushed the bolt back into battery after a fresh round had been fed.
The APIB principle permits a higher rate of fire and lighter bolt than a simple blowback, but the length and speed of the travel of the bolt within the chamber are limited by the stresses the sliding motion, executed under high gas pressure, puts on the case. To keep these within limits, the bolt needs to be very heavy or the barrel short. The designers for the MK 108 opted for a short barrel, permitting a light bolt and a fairly high rate of fire. --Flame 歡迎泡茶 2011年7月15日 (五) 00:39 (UTC)
外部連結已修改
各位維基人：
我剛剛修改了MK-108航空機炮中的1個外部連結，請大家仔細檢查我的編輯。如果您有疑問，或者需要讓機器人忽略某個鏈接甚至整個頁面，請訪問這個簡單的FAQ獲取更多信息。我進行了以下修改：
- 向 http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=1041 中加入存檔鏈接 https://web.archive.org/web/20090113130439/http://www.nationalmuseum.af.mil/factsheets/factsheet.asp?id=1041
有關機器人修正錯誤的詳情請參閱FAQ。
祝編安。—InternetArchiveBot (報告軟件缺陷) 2017年6月9日 (五) 15:00 (UTC)
外部連結已修改
各位維基人：
我剛剛修改了MK-108航空機炮中的1個外部連結，請大家仔細檢查我的編輯。如果您有疑問，或者需要讓機器人忽略某個鏈接甚至整個頁面，請訪問這個簡單的FAQ獲取更多信息。我進行了以下修改：
- 向 http://www.quarry.nildram.co.uk/WW2guneffect.htm 中加入存檔鏈接 https://web.archive.org/web/20110520120112/http://www.quarry.nildram.co.uk/WW2guneffect.htm
有關機器人修正錯誤的詳情請參閱FAQ。