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There are a number of types of breech blocks used in automatic weapons. The most common, of course, is the bolt, although we frequently extend that term to include bolts that do not rotate. There is also the sliding breech block.

In classifying automatic weapons, the distinction is frequently made between long recoil and short recoil operation

I have seen several weapons with sliding breech blocks described as using long recoil. However, it appears that the long/short recoil distinction is meaningless unless the breech block moves fore and aft (e.g. a bolt). I cannot conceive of any sliding breech block configuration where the breech block would not move entirely with the barrel.

Is there a distinction between long and short recoil when the breech block is not a bolt or bolt variant? Is there a long/short recoil distinction with a sliding bolt?
Posts: 12 | Registered: January 10, 2021Reply With QuoteReport This Post
Sigless in
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I am not an engineer so if I say something inaccurate I am happy to be corrected.

If I understand correctly, long recoil is when the piston that tappets off gas from the bore moves the entire length of cycle along with the bolt carrier.

Short recoil is when the piston moves just far enough to impart sufficient kinetic energy to the bolt carrier to throw it the rest of the length of travel necessary to cycle the action.

To my understanding, long vs. short has to do with the distance which the piston travels. If this is inaccurate or overly simplistic I will defer to the real experts.
Posts: 13696 | Location: The Edge of the Ozarks | Registered: December 04, 2003Reply With QuoteReport This Post
semi-reformed sailor
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Wait till you read about these cannons that use a blowback type of recoil....I used to work on these in the service....

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I didn’t try to answer because I’m still not quite sure what the question is.

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Posts: 18466 | Location: 18th & Fairfax  | Registered: May 17, 2003Reply With QuoteReport This Post
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You might define the elements a bit closer because until now it leaves the impression that you want to compare the principle of Webley Fosbery revolver with a HK G11. I doubt this is what you are looking for. Your feedback will therefore be appreciated.
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Long Recoil:


Frommer Stop

Browning A5

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Posts: 24678 | Location: Johnson City/Elizabethton, TN | Registered: April 28, 2012Reply With QuoteReport This Post
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The rearward movement of the barrel cycles a recoil operated weapon. Most automatic pistols over 0.38 use this method. It is also common on heavy machine guns, such as the M2 and 40mm Bofors. It is not common on rifles but is sometimes used, such as in the M-82. It is common for semiautomatic shotguns.

In a blowback operation, the barrel remains fixed. The mass of the breech and any spring resists the opening of the barrel until safe. This is the most common method used in automatic pistols under .38. The PPK uses this system. This method is rarely used in rifles. An oddball is the 20mm Oerlikon. This method is also used, combined with some delaying mechanism on larger calibers, such as in the MP-5.

In gas operation, some of the expanding propellant is tapped off the barrel and used to cycle. This is the most common system used in rifles and light machine guns. It is rarely used in pistols.

There are sometimes combinations, such as the MG42 that uses gas and recoil.

Recoil operated weapons are often divided into long recoil and short recoil. In long recoil, the breech block remains closed until the barrel reaches the end of its travel. E.g. Bofors, and most semiautomatic shotguns. In short recoil, the breech block opens before the end of travel. E.g., M-2 BMG.
Posts: 12 | Registered: January 10, 2021Reply With QuoteReport This Post
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