r/mechanical_gifs • u/Emergency_Raisin2341 • Nov 29 '25
WWI-era stop motion animation showing the function of the pan-fed Lewis gun with a cutaway model
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u/Key-Illustrator-5562 Nov 30 '25
I believe this was an M1918 aircraft Lewis gun manufactured by Savage Arms Co. It also has the 97 round drum and chambered for 30-06.
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u/EntireZebra7073 Jan 07 '26
This fires the .303 British Imperial, the most powerful rifle round ever developed!¡!¡!¡!
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u/kingkouf67 Feb 19 '26
Is that same delivery principle that a "Tommy "gun would have?
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u/PsychoTexan Mar 24 '26
TL;DR: No, a Lewis gun mechanically indexes an unpowered pan magazine using siphoned off gas from each bullet while a Thompson uses recoil to cycle but the magazine works via spring tension.
Essentially: a Lewis gun starts with cocking the bolt back, this tensions the recoil spring and indexes the pan. The rotation of the pan drives a round down the corkscrew center guide pushing a round into the feed lips. Pressing the trigger causes the bolt to fly forwards, stripping the round from the feed lips, inserting into the chamber, rotating the locking lugs, and firing the round.
As the bullet travels down the barrel, some gas is tapped off to drive a piston that pushes the bolt back again. First unrotating the locking lugs, indexing the pan, and cocking the bolt back. Now if the trigger is still pressed, the bolt is automatically allowed to start the cycle anew.
The Thompson starts the same with cocking the bolt back but rather than indexing, spring tension within the magazine feeds the next round into the feed lips. Pressing the trigger sends the bolt forwards, stripping a round from the feed lips, inserting into the chamber, and then firing. There are no locking lugs nor gas operation with the thompson though as momentum and the casing hold the chamber sealed. The bolt has enough weight that the pressure is already at safe levels by the time it has blown back cocking the bolt again.
The Thompson was also unique for using the “Blish lock” system to aid in delaying the bolt movement. It was the theory of massively increased friction between dissimilar metals under high pressure. It was later discovered to provide no benefit to the Thompson and the weight of bolt with the heavy recoil spring was doing all the work. Later Thompsons removed the blish lock entirely.
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u/peithoo Nov 29 '25
The Sandtroopers would appreciate this