Not quite.
"EVALUATION OF PRETREATMENT PROCESSES AND LONG-TERM STORAGE ON MAGAZINE SPRING FOR THE M14, 7.62MM, RIFLE," LaRiviere, Feb 1966, Springfield Armory, MA
"PERFORMANCE OF 5.56-MM 30 ROUND MAGAZINES AFTER EXTENDED LOADED STORAGE," Foltz, Grego, Escalona and Ritschel, ARDEC, Picatinny Arsenal NJ
The purpose of this test was to determine if storing of a loaded 5.56-mm, 30 round tan follower magazine [part number (P/N) 13021312] with M855 ball ammunition for an extended period of up to 5 yr would degrade the magazine spring to the point that its spring force would not properly load ammunition into the host weapons: the M4A1 and M16A4. It is important that the magazine spring supply enough force to chamber the next cartridge properly, otherwise the weapon may misfire (ref. 1). . .
Beginning in April 2011, three hundred 5.56-mm, 30 round magazines were loaded with M855 ammunition. Prior to loading, each magazine’s spring force was measured in accordance with (IAW) DR 13021312, note 2, which allows the spring force when depressed 0.25 in. to be between 2.5 and 3.5 lb. Once loaded, all 300 magazines were placed in a storage bunker located at the U.S. Army Armament Research, Development and Engineering Center, Picatinny Arsenal, NJ. In 6 month intervals, over the 5-yr period, 30 magazines were removed from storage and fired, 15 on an M4A1 and 15 on an M16A4. The cyclic rate of the weapon was recorded as well as the spring force of the magazine when empty.
In a previous evaluation of long term storage conducted on M14 magazine springs, it was shown that the majority of spring force degradation due to extended storage occurs in the first two years, as shown in figure 1. Therefore, it is probable that if the 5.56-mm, 30 round magazines still fire properly after 2 yr of storage, then longer intervals of storage would not cause system failure since the majority of spring set would have already occurred (ref. 4).
There is a loss of spring load due to extended compression.
HOWEVER:
The minimum spring strength specified on the drawing IS NOT the the minimum strength required for reliable operation. Magazine springs can be considerably softer than the print minimum and still work fine. Think about it, they have to be otherwise many springs wouldn't work correctly right out of the box.
Also note the curves flatten out after the first two years, so it is only after two years that continuous compression that there is no further degradation of spring strength.
So, the next question: How many cycles to wear out a spring?
Well, the M14 test is try and answer this and configure a machine to compress about 20 M14 magazine springs from empty length to full magazine length. After 10,000 cycles the springs lost just over 3/4 pound of strength. Since the M16 magazine spring is a different material, there might be some differences in spring life.
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