I've never down loaded mags, but I have had to replace mag springs in a M&P 40 1.0 LE trade in I bought. It was doing the same thing you described. Fixed them right up. I picked them up at Midwest Gun Works. Smith & Wesson M&P / M&P M2.0 Magazine Spring

 

I have owned a wide variety of semi-auto pistols over the years, and never had this problem before. I might gradually replace the mags springs with Wolff extra-power ones. It pisses me off that Smith has used cheap wire for these springs! Thanks for the info.

 

Same here. Had issues with some of the older 17 round 9MM magazines dating back to my 1.0 M&P. I bought new springs from Wolff Gun Springs that are 10% stronger than the factory magazine springs. I just bought a 10 pack because I knew I needed several at the time and figured at some point I'd need more.

https://www.gunsprings.com/SMITH+&+WESSON/M&P+SERIES+-+9mm,++.40/.357+/cID1/mID58/dID262#1004

Yes, mine are fully loaded. Yes, mine wasn't locking the slide back when the last round was fired.

You can see several of the old springs lined up with two of the new springs to get an idea of how much the springs had compressed over the years.

I've had issues with Shield Plus magazine springs. No replacements (extra strength) available for those yet so I'm downloading those mags by 1 round each.

So far, no issues with the Wolf 10+ strength magazine springs.

 

Thanks for the replies. I just sent this e-mail to Smith & Wesson.

Hello. I am writing to let you know that I am really disppointed in a product I have. 10 years ago, I bought an almost new Gen 1 M&P 9. I then puchased 20 new factory mags for it. Yesterday, I switched out the 3 mags that I keep loaded at all times that had been loaded for approximately 3 years and I checked the slide lock in the pistol with the 3 mags I just unloaded. I was unpleasantly surprised that 1 of the 3 no longer locked the slde back on an empty mag. Now I have had to purchase 20 Wolff +10% springs to remedy the problem and restore my confidence in what was otherwise a good pistol. This has cost me over $100 and is directly due to crappy wire used in your springs. To say I am pissed off is an understatement.

I don't expect them to do anything, but I damn sure will let them know.

 

I download by 1 with most of my mags.

Years ago, I had the same issue with Hk USPc mags and Beretta 92 mags. I left my carry gun fully loaded for a few months. Then, the slide would not lock back reliably when I shot the gun with that mag. The gun still functioned, but would not lock back. I switched mags and did the same thing - it happened again.... And again.

I ended up getting +10% Wolff springs and replaced the affected mags. And for the HK mags, I just replaced all 6 springs.

People argue that springs don't wear out from simply being loaded, and that it is thru use that they wear out. This proves that this is not always true. And, the Wolff Springs website has a page that says that the springs can wear out thru leaving the mag loaded all the time - and they make the springs.

Since then, I have underloaded almost all my mags - and never had an issue again.

Underloading was a trick that almost everyone did back in the 1980s and early 1990s too.

The only mags I don't usually do this with are Glock mags. For some reason, they don't seem to suffer from this issue.

 

No.
My M&P9 mags date back to ‘07, have never been cleaned, are left loaded for extended periods of time, and all function flawlessly.
I think I have 14-15 of them.

Same thing with my 1911 mags, but some of those are much older.

 

Thank you. I have owned SIGs, Glocks, Brownings and Rugers and this is the first time I have noticed the problem.

 

Using fully loaded magazines is fine when the pistol has locked back due to an empty magazine. The situation is quite different when a tactical reload is being executed; round chambered, slide in battery and now you want to drive another fully loaded magazine into gun hoping it will engage the magazine catch. We all know how much tension is in the magazine when that last round is loaded. When inserting the full magazine into the gun, slide in battery, the magazine spring has to be compressed 10+1 / 17+1/ 20+ 1 etc. there is literally almost no room at the bottom of the magazine for the spring to compress another 1/2 bullet diameter which is what needs to occur to lock the magazine into the gun. Not a big deal on the one way range, in real-ville, having a full capacity magazine not fully engage and drop out on the next fired round leaves one with a full magazine between their legs with an unloaded pistol now in full battery. Looking pretty silly standing in the doorway at the adversary with your empty paper weight. It's smart gear prep to download by one round if you are anywhere but the range.

 

mp9werks makes a darn good point here.

Now he's got me wondering if I've contributed to the Shield Plus magazine spring issues by chambering the top round, removing the magazine and inserting another round into it before forcing it back up into the magazine well. I'm now downloading those by one round (started awhile back when I was fiddling with the pistol one day after unloading my carry mags and found out the followers weren't rising far enough to lock the slide back. Still looking for someone making replacement +10% springs for them. Wolff's got the big mags. covered.

 

It really comes down to the brand probably. Some mags seem to have no issues, and others do.

I have read stories of 1911 mags being loaded for decades, and having no issues.

But like I said, I personally had issues with 2 specific brands.

I just generally underload by 1 in most of my guns. I have never had to replace a mag spring since.

But, do whatever you want to do yourself...

 

I have read stories of 1911 mags being loaded for decades, and having no issues.

It's more than "stories". It's been studied ad nauseum and the the conclusions are, magazine springs do not fatigue from prolonged compression, they fatigue from high cycling operation.

 

I make it a habit to change my mag springs every 5ish years to avoid malfunctions that may occur. It’s cheap insurance.
Wolff +10% is my go to spring.

 

I never bothered with that Shield Plus mag modification that some do to get 13 rounds into the magazine (the follower surgery). I only put 12 in my mags anyway, so that problem is a non issue for me

 

You can get a run of bad springs at times.

A few years back one topic of discussion on the CZ Forum was about trigger return springs. CZ got a bad lot/shipment of them from their vendor and owners were having a hard time keeping their new pistols up and running. Left a window for other vendors to develop/sell their own trigger return springs.

One guy bought a new P09 9MM and loved it. After a range trip or two and some dry firing the trigger return spring broke. He called CZ, sent it back, they fixed it and shipped it back to him. A couple weeks later the trigger return spring broke again. He got it fixed by CZ and sold it the week it came back.

Sooner or later all of us will buy something that breaks/wears out early or in a weird fashion.

 

Well, I had to replace 8 Beretta 92 mag springs for this reason, and 6 HK USPc mag springs. Those are pretty good brands.

They were loaded 100% for about 3 months each time when I started to have an issue. Like clockwork - the slide would fail to lock back on a range trip after doing that. Mag by mag by mag... Over time...

I have about 25 Beretta 92 mags. After changing those 8 springs with +10% springs because of this issue. I stopped keeping 15 in the mag. I keep 14 in the mag. NEVER had another problem with this again. Most of those mags are easily 10-15 years old. They are factory mags too.

Future HK USPC/P2000 mags... I only loaded 12 rounds instead of the full 13. Never had another issue with the slide not locking back again either with those mags.

Also, the +10% replacement mags for the HK were almost TOO strong. The gun barely functioned until the mag springs broke in. They were pushing up with too much force, and you could feel the slide struggling to function. It took a while for that to go away with the +10% mags in the HK.

So, by not loading to 13 round on HK mags I purchased after that, I eliminated that whole issue...

So, not much else to say. That is proof. Case closed 😁

 

I’ve had exactly 1 bad spring in a Beretta mag, and it was a GI mag. I simply pulled the spring back out to a slightly longer length and it ran good again. I carried that M9 in combat. Never had the problem before or since. In fact I have never had a pistol mag go bad with any brand. If you are having so many problems….maybe it might be something you are doing.

 

20 mags… .and left unused/empty for years. That puzzles me.

 

Some of us buy spares and put away for the time we feel we might need them.

Some of us buy spares and the next thing we know we've got a bunch of empty ammo boxes.

Then, the next thing you know, we're feeling the need for more spare magazines to put away for some time we might need them. Vicious circle.

 

Magazine springs are considered a wear item, just like the brake pads in you car.

 

As well as all the other assorted springs in your gun. I’d be more concerned with recoil springs going bad in guns like the Shield, P365, Hellcat etc., than a mag spring. I’ve read those should be replaced at 1,500-3,000 round intervals.

At any rate, know your gun and plan accordingly….

 

So...I went and bought 20 Wolff +10% extra-power springs, and went through and changed out all of the springs that were shorter than the new ones. Strangely enough there were some factory springs that when removed were as long as the Wolff springs. It is possible I guess that I switched some of these out years ago and don't remember doing so. I downloaded the three mags that I keep loaded to fifteen at the suggestion of mp9werks. What he said made sense, and it is the very same reason that I keep a 30 round rifle mag downloaded to 28, and always have. He suggested one, but I downloaded by two. If I need more than 15 rounds in an altercation, I have other problems.

 

When I had problems with the older (from my 1.0 9MM) 17 round magazines they would feed ammo to the pistol fine. They would not lock the slide back after the last round.

I field stripped the pistol and inserted the magazines. The follower would not push the magazine release up all the way. The new magazines that came with the 2.0 9MM would push the slide lock up all the way. Some of the older ones would not. The Wolff Springs 10% stronger springs fixed that.

Another picture of the magazines to show a visual difference the older springs had compressed over the years (for many years they weren't even loaded.)

Doesn't look like much, but it was enough. The springs are the same length new and have the same number of coils. These were a mix of 1.0 and 2.0 mag. springs (1.0 are the short ones) with the two longer ones being out of the 2.0 9MM magazines that came with the 2.0 5" FDE 9MM.

Never had the issue with the 1.0 .40 S&W magazines. S&W probably doesn't make the magazines. They contract them out to another company. That company may contract out some parts (such as the material the springs are made from) to another company. Some times companies get in bad lots of raw materials or parts and they end up causing problems with the consumer of the end product.

 

I don't load them down, but I don't +1 them.

Regarding springs,

I worked in product development for a computer company and had the opportunity to fabricate various things. On one occasion I needed a precision spring
and had to have some made. I met a Mechanical Engineer at a spring company (he called himself a springineer) who LOVED springs, weird I know but he was
a GR8 resource. After explaining the compression / expansion types of springs, and where they are expected to be linear and are not linear in rated force. I
asked about "spring set" where a spring obtains a "memory" after being under load for a long period of time. We were both firearm owners and he (with his
springineer hat on) explained that:

Many companies deliver firearms with two magazines the second as a backup / spare, but going further he advised me to rotate loaded unloaded times to prevent spring
set, or compression memory.

Take a used spring from a mag, hold it against a new one, and the used one will be shorter and weaker... of this I have no doubt as I almost crashed and burned
an important invitational match (luckily the timer was faulty during my run and I got a re-shoot) due to weak springs (poor feed on the last two rounds) that despite
the Springineer's advice I had previously left loaded, I do not do that now.

So, today I rotate them on an informal timetable to prevent feed jams.

After meeting the spring engineer I "NEVER" cut a spring to get a particular "rating" due to his insistence that spring length, load/unload force (Danger
of powered flight / force versus free flight / force I think he called it) is very different on springs that are too short for the application.