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Most metallurgists agree with what you related. Many actual users and some metallurgists disagree. As I stated I was merely relaying what some M&P user have claimed work for them and make no argument for or against the practice.
However, Wolff Springs feels that magazine springs kept loaded suffer more fatigue faster:
5. How often should I change magazine spring? Should I unload my magazines, rotate magazines, load with fewer than the maximum rounds?
Magazine springs in semi-auto pistols are one of the most critical springs and are the subject of much debate and concern. Magazines which are kept fully loaded for long periods of time, such as in law enforcement and personal/home defense applications, will generally be subject to more fatigue than the weekend shooter's magazine springs in which the magazines are loaded up only when shooting.
Magazine design and capacity also affect the longevity of the spring. In many older pistol designs, maximum capacity was not the always the goal such as with the 7 round 1911 Colt magazines will last for years fully loaded. There was room for more spring material in these guns which reduces overall stress and increases the usable life of the spring.
More recently higher capacity magazine have become popular. These are designed to hold more rounds with less spring material often in the same space. This puts more stress on the spring and will cause it to fatigue at a faster rate. Unloading these magazines a round or two will help the life of the spring. Rotating fully loaded magazines will also help the problem somewhat but it is not always practical.
In applications where the magazine must be kept loaded at all times, a high quality magazine spring such as Wolff extra power magazine springs, will provide maximum life. Regular replacement of magazine springs will provide the best defense against failure from weak magazine springs. Regular shooting of the pistol is the best way to be sure the springs are still functioning reliably.
Some testing on airgun mainsprings http://www.network54.com/Forum/79537...++damage-++n-t
"OBJECTIVE: To determine the effect on a mainspring if airgun is left cocked for an extended period.
Preparation: Airgun was disassembled, thoroughly degreased, examined, lightly lubed with a mixture of Silicone oil & moly, and then reassembled.
Procedure: After reassembly, airgun was fired 10 times to eliminate any excess lubricant which would contribute to dieseling. Muzzle velocity recorded at each period in time was the average of 5 shots. VO = prior to test; V1 = gun left cocked for 1 week, 24 hrs per day (168 hrs); V2 =gun left cocked for 2 weeks, 24 hrs/day (336 hrs); V4= left cocked for 4 weeks (672 hrs); V12 = left cocked for 12 weeks (2,016 hrs) and V24 = 24 weeks (4,032 hrs).
At the end o each period, the gun as uncocked and left uncocked for 72 hrs to allow the spring to regain as much as possible of its original power (memory effect). The gun was cocked and uncocked a number of times to get the cylinder walls lubed and then 2 shots fired over a chrono. The average of these 2 shots were taken.
All pellets have been sized and weighed then batched according to weight, so all pellets used in this test were of uniform size and weight. All airguns were .177 cal and all velocity readings are in feet per second.
V0 V1 V2 V4 V12 V24 % Vel Decrease
HW30 655 648 630 592 521 481 26.6
HW50 705 682 678 640 565 513 27.2
HW35 715 698 689 652 576 533 25.5
R1 975 965 944 891 789 739 24.2
Vulcan3 818 808 785 739 640 599 26.8
Webley
Hawk 655 638 630 589 519 476 27.3
BSA Merc 695 679 668 630 552 511 26.5
FWB124 795 774 770 728 645 596 25.0
There were 2 spring failures (breakage) suffered by the Webley Hawk on weeks 4 and 12. No others suffered the same fate. I attribute spring failure to the absence of a spring guide in this make and model. While the percentage reduction in velocities varied, reduction was generally around 25% of original velocity taken prior to commencement of test.
It should be noted that these percentage decreases are theoretically optimistic as the air gunner would more likely experience reductions in velocity greater than the statistics shown here. Dieseling, weight & size (diameter.) of pellets used, improper lubrication, temperature, conditions of usage etc. can all have an adverse impact on the life and power of a mainspring. This test does show that leaving a spring airgun cocked, no matter for how long, will adversely affect the life and power of any mainspring. Custom springs will be more resistant to decrease in power but the process will still occur over a longer period of time. I do not suggest that you change the ways you hunt but I point out, as Tom Gaylord has done very well, that be prepared to pay the price of higher maintenance."
And finally, I can tell you from my own experience that drag race engine builders which use extremely high pressure springs to prevent valve float by large valves at very high rpm recommend backing off the rocker arms whenever possible to reduce spring fatigue.
However, Wolff Springs feels that magazine springs kept loaded suffer more fatigue faster:
5. How often should I change magazine spring? Should I unload my magazines, rotate magazines, load with fewer than the maximum rounds?
Magazine springs in semi-auto pistols are one of the most critical springs and are the subject of much debate and concern. Magazines which are kept fully loaded for long periods of time, such as in law enforcement and personal/home defense applications, will generally be subject to more fatigue than the weekend shooter's magazine springs in which the magazines are loaded up only when shooting.
Magazine design and capacity also affect the longevity of the spring. In many older pistol designs, maximum capacity was not the always the goal such as with the 7 round 1911 Colt magazines will last for years fully loaded. There was room for more spring material in these guns which reduces overall stress and increases the usable life of the spring.
More recently higher capacity magazine have become popular. These are designed to hold more rounds with less spring material often in the same space. This puts more stress on the spring and will cause it to fatigue at a faster rate. Unloading these magazines a round or two will help the life of the spring. Rotating fully loaded magazines will also help the problem somewhat but it is not always practical.
In applications where the magazine must be kept loaded at all times, a high quality magazine spring such as Wolff extra power magazine springs, will provide maximum life. Regular replacement of magazine springs will provide the best defense against failure from weak magazine springs. Regular shooting of the pistol is the best way to be sure the springs are still functioning reliably.
Some testing on airgun mainsprings http://www.network54.com/Forum/79537...++damage-++n-t
"OBJECTIVE: To determine the effect on a mainspring if airgun is left cocked for an extended period.
Preparation: Airgun was disassembled, thoroughly degreased, examined, lightly lubed with a mixture of Silicone oil & moly, and then reassembled.
Procedure: After reassembly, airgun was fired 10 times to eliminate any excess lubricant which would contribute to dieseling. Muzzle velocity recorded at each period in time was the average of 5 shots. VO = prior to test; V1 = gun left cocked for 1 week, 24 hrs per day (168 hrs); V2 =gun left cocked for 2 weeks, 24 hrs/day (336 hrs); V4= left cocked for 4 weeks (672 hrs); V12 = left cocked for 12 weeks (2,016 hrs) and V24 = 24 weeks (4,032 hrs).
At the end o each period, the gun as uncocked and left uncocked for 72 hrs to allow the spring to regain as much as possible of its original power (memory effect). The gun was cocked and uncocked a number of times to get the cylinder walls lubed and then 2 shots fired over a chrono. The average of these 2 shots were taken.
All pellets have been sized and weighed then batched according to weight, so all pellets used in this test were of uniform size and weight. All airguns were .177 cal and all velocity readings are in feet per second.
V0 V1 V2 V4 V12 V24 % Vel Decrease
HW30 655 648 630 592 521 481 26.6
HW50 705 682 678 640 565 513 27.2
HW35 715 698 689 652 576 533 25.5
R1 975 965 944 891 789 739 24.2
Vulcan3 818 808 785 739 640 599 26.8
Webley
Hawk 655 638 630 589 519 476 27.3
BSA Merc 695 679 668 630 552 511 26.5
FWB124 795 774 770 728 645 596 25.0
There were 2 spring failures (breakage) suffered by the Webley Hawk on weeks 4 and 12. No others suffered the same fate. I attribute spring failure to the absence of a spring guide in this make and model. While the percentage reduction in velocities varied, reduction was generally around 25% of original velocity taken prior to commencement of test.
It should be noted that these percentage decreases are theoretically optimistic as the air gunner would more likely experience reductions in velocity greater than the statistics shown here. Dieseling, weight & size (diameter.) of pellets used, improper lubrication, temperature, conditions of usage etc. can all have an adverse impact on the life and power of a mainspring. This test does show that leaving a spring airgun cocked, no matter for how long, will adversely affect the life and power of any mainspring. Custom springs will be more resistant to decrease in power but the process will still occur over a longer period of time. I do not suggest that you change the ways you hunt but I point out, as Tom Gaylord has done very well, that be prepared to pay the price of higher maintenance."
And finally, I can tell you from my own experience that drag race engine builders which use extremely high pressure springs to prevent valve float by large valves at very high rpm recommend backing off the rocker arms whenever possible to reduce spring fatigue.
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