Shield Plus Slide Not Locking Open - not thumb

[flyingbrass]

My Shield Plus didn't want to lock on empty from new. I'm well aware of the thumb touching the slide stop being a common cause of this problem, but that's not what is happening here. I have an original "1.0" Shield that taught me the thumb lesson.

The Plus was on the verge of wanting to lock the slide open, as in it would maybe 10-20% of the time. I sent it back to S&W and included a note with the problems:

1) Completely dead front night sight
2) Optic cover plate was sitting above flush at the front (is the problem with the cover plate or the optic slot?)
3) Failure to lock slide open with 10 round mag (the 13 worked at first)
4) Hitch in safety lever (though I mentioned this wasn't a big deal)

I received the pistol back 33 days later. The front sight had been replaced. The optic cover now sits flush with the top of the slide, though daylight can still be seen underneath. I hope the slot itself is in spec, but I don't know and still wonder. I was sent 2 new magazines. The safety is the same. The repair notes are sparse and vague about what was done.

I prefer to work on and solve issues myself. This is only the second time I've sent a gun back to the factory for anything. My previous experience with Ruger was much quicker, and their repair notes were more detailed.

When I tested the returned Plus, the slide wouldn't lock open at all with any of the now 4 factory magazines. It would occasionally lock open before. The same ammo has no problem locking slides open in all of my other pistols, including my original earlier Shield "1.0".

The Plus' slide stop releases far easier than my early Shield. During my first shooting session, the slide dropped once when I set the pistol down on the bench after removing the magazine. This is the opposite of the usual with these and similar S&W pistols. Usually, slide stops are relatively difficult to disengage. Looking closely and comparing, the slide stop notch on the Plus is chamfered more than my 1.0 Shield. This reduces its engagement depth.

The Plus's magazines, all 4 of them, don't exert much upward pressure on the slide stop compared to the earlier Shield's magzines (which now have Wolff springs, but factory were about the same). This, I believe, is the main problem. I don't yet know the cause. It could be dimensions of the slide stop itself (relationship of nub that contacts follower to part that engages the slide), the slide stop spring pressure, or, the worst case for a repair scenario, the position of the magazine within the frame (magazine sitting too low). BTW, the slide will lock every time if I deliberately push the magazine up into the frame when shooting.

I put a 500 mL water bottle on my food scale with fishing line tied around the top of the bottle and a loop several inches away. I zeroed the scale. Then I hooked the fishing line around the slide stop and lifted the upside down frame until the slide stop had fully raised. Then I backed off until the slide stop just began to lower. I read how much weight the scale lost. Measuring slide stop spring tension this way isn't easy or accurate, but it's the best method I could come up with.

The figures varied, but I settled on about 7.5 oz average for the original Shield and about 11.5 oz for the Plus. Aha! This must be the problem. Also, I found that the edge of the Plus' spring was contacting the edge of the locking block which caused extra resistance as the slide stop neared its most upward position.

In addition, the top of the slide stop where the spring rides was the typical stamped ugliness of S&W parts. I smoothed it out and lightly broke all of the other edges that might catch on either the locking block or the frame to add resistance. I reshaped the slide stop spring slightly, which brought the measured weight down to about the same as my orginal Shield that works flawlessly. The reshaping also brought the edge of the circle part of the spring end slightly away from the locking block. It made little to no contact, while there had been a hitch from this before. Is the spring supposed to touch at all?

After this, the magazine follower still wasn't as vigorous at raising the slide stop as my 1.0 Shield, but at least it no longer had a hitch near its highest position and was raising better. I was proud of myself and thought I had solved the problem.

I test fired using single rounds in a magazine. For the first 3-4 rounds the slide locked open. I then tried a different magazine, which didn't lock, then I went back to the first magazine, which no longer locked. I tried the other mags with only an occasional lock. Damn.

I put my Shield 1.0 slide/barrel/RSA on the Plus' frame. The combo wouldn't lock. I swapped recoil springs, putting the 1.0 Shield's spring in the Plus. No change. I put the Plus' slide/barrel/RSA on my 1.0 Shield, which locked.

I think it's safe to say the problem is narrowed to the Plus' "lower."

To double check ammo, I deliberately limp wristed the 1.0 Shield shooting with one hand. It locked open 3 times in a row. The problem is not from weak ammo or a limp wrist. FWIW, the ammo is 115 grain FMJ that averages 1120 - 1160 FPS out of a CZ-75 depending on temperature. I've never had failures with slides locking open in other pistols with this power level or even quite a bit lower.

The attached pictures show before and after smoothing the top edge of the slide stop and where the end of the spring was/is making contact with the locking block. What I did helped a little, but it hasn't solved the problem.

I'd appreciate any suggestions. How common is this?

I'm considering asking S&W to send me a new slide stop and new slide stop spring to try. If that doesn't help, I'm thinking the problem is most likely with the location of the magazine within the frame, as in the magazine isn't being held quite high enough, which would be a more involved repair. I'd rather not send this pistol back yet again for who knows how long. If I do and it comes back the same I'll be really ticked off. I can envision a tech firing it once, getting slide lock that time, and saying ok, it's fine - couldn't replicate the reported issue.

I've been shooting semi-auto pistols for over 35 years, and I know when something isn't right. This isn't right.

 

[haywood]

Do you have a Gunsmith available to show the gun to and explain what you have found? Maybe that approach would work instead of sending it in.

 

[flyingbrass]

Update:

I called S&W. They wouldn't send or sell me a slide stop. I asked if slide stops for the Plus and earlier Shield models are the same and was told they are not. So, I sent the pistol back. One day short of 6 weeks later it returned with a note that they couldn't duplicate the problem, which is what I thought might happen. I probably shouldn't have cleaned it before sending it in. Last time I cleaned it, the slide locked the first several times and then went back to its usual behavior.

After seeing an eBay add offering a Shield slide stop compatible with 1.0, 2.0 and Plus models both in 9mm and .40 S&W (and .30 SC), I suspected, contrary to what S&W had told me, that all the slide stops might actually be the same. I ordered 2 Shield slide stops from Midwest. After shipping, one would have cost $17 and change, or 2 for $25.55. Might as well buy 2 so I'll have a spare. Written on the bag I received is 422160000, which I assume is the part number.

I compared some measurements of my original Plus' slide stop and the two that I bought. All were very close, within expected manufacturing variations. They are the same.

I had already bought a couple extra slide stop springs from S&W. Funny that they'll sell the springs directly but not the slide stops. BTW, S&W wouldn't sell me a trigger return spring either. They said all of this stuff is factory installation only. This is ridiculous. These parts from resellers cost more, plus I'd rather buy from S&W directly to be sure I'm getting the correct part. S&W should revise their parts policies.

I got greedy and tried to further lighten my original slide stop spring that I had previously altered. I messed up, then reshaped it too many times in attempts to fix and broke it.

This time I used a homemade spring scale to measure tension required to lift the slide stop into locking position with a new slide stop spring and compared with my original Shield. I bent the new spring as much as I could while still leaving it barely contacting the slide stop when the stop was bottomed within the locking block. This reduced the tension a little and brought it on par with my original Shield. I deburred the rough edges of the new slide stop (didn't touch the part that engages the slide). I lubed the slide stop and where it rides in the locking block with Hornady One Shot Cleaner and Lube before reassembling.

Last week I test fired by firing a single round in each of my 4 magazines, repeating this. Out of 49 single rounds fired this way, the slide locked open 47 times, and the 2 failures were definitely my fault. In trying various grips I let my thumb ride too far forward a couple times. 20 or so of those slide locks were single-handed firing with a deliberately softish wrist and arm, so the locking is now quite positive. Today I again fired to slide lock 12 more times without trouble.

The problem seems to be solved with the new slide stop (knock on wood). I doubt the new spring made any difference because the original that I had altered was a little lighter than I got after bending the new one. I should have just left the original spring alone after the first reworking instead of attempting to reduce it further.

I don't know what the problem was with the original slide stop, but I suspect it may have been minor variations of the angle or shape of the part that engages the slide. These stamped parts are coarse on the edges, and perhaps the orginal was out of whack just enough to cause problems. Or there may have been a dimensional issue not readily detectable by caliper measurements.

 

[Kenroycon]

I think it is the assembly of the base of the mag that causes the issue. The metal piece that goes over the spring, pops out from the frame. I think it happens when loading rounds or reassembling the mag(sliding the last piece on makes the metal piece move) I took mine apart then reassembled it, making sure to keep it from sliding toward the front out from under the frame. The slide locks back now
and all 13 rounds still fit.

 

[crosseyedshooter]

Wow, what an ordeal! I have two Shield Plus, one regular and the other Optic Ready, that have gone through multiple pistol classes without issue. I like them so much that I bought a third for back-up in case one has to go in for service.

You really have a lot of patience to go through all of that troubleshooting and experimentation. Thank you for sharing your knowledge and experience.

 

[flyingbrass]

I think it is the assembly of the base of the mag that causes the issue. The metal piece that goes over the spring, pops out from the frame. I think it happens when loading rounds or reassembling the mag(sliding the last piece on makes the metal piece move) I took mine apart then reassembled it, making sure to keep it from sliding toward the front out from under the frame. The slide locks back now
and all 13 rounds still fit.

I don't understand exactly what you mean, but the spring's upward pressure on the follower with an empty magazine is so little in these magazines that anything affecting spring tension could easily cause the slide stop to not be pressed up enough.

In my case though, 4 factory magazines that hadn't been disassembled acted the same.

 

[flyingbrass]

Wow, what an ordeal! I have two Shield Plus, one regular and the other Optic Ready, that have gone through multiple pistol classes without issue. I like them so much that I bought a third for back-up in case one has to go in for service.

You really have a lot of patience to go through all of that troubleshooting and experimentation. Thank you for sharing your knowledge and experience.

Yeah, not very fun for a new pistol. I'm not impressed with S&W's lack of quality control, at least not at the prices they are charging. Out of the box mine had a dead front night sight, a poorly fit optic cover, and the slide locking issue. The thumb safety also has a bit of a hitch when moving it up to engage, which I will address when I remove the action block to extend the thumb safety lever.

How hard do you have to press the slide stop to drop the slides from lock on your Plus pistols? Even with my new slide stop, it is quite easy. Usually, the M&P pistols are relatively difficult.

 

[flyingbrass]

An update now that I know a bit more:

The issue with the slide dropping too easily when locked open turned out to be the shape of the slide stop notch in the slide. I suspected this may have been an issue early on, but I was reluctant to do anything to the slide. See the attached picture for comparison of my 1.0 Shield and the Plus slide stop notches. There was more chamfer on the Plus.

This is all very touchy and sensitive. The replacement slide stop I used in the Plus happened to work a little better than the original, but it didn't completely solve the problem. The slide was still somewhat reluctant to lock open and dropped easily when pressing on the slide stop.

I used a small triangular needle file to slightly reshape the slide stop notch. I didn't take off much material. This made a world of difference, and now the Plus' slide is holding open as solidly as my 1.0. I can't make the slide drop using my right thumb with as much pressure as I can muster, when before just a slight touch would do so. I can force the slide to drop on both pistols by pressing the slide stop quite hard with my left thumb, and both pistols require similar pressure.

Very small differences in the slot affect the effort required to drop the slide by depressing the slide stop. With this in mind, tune to your preference. I prefer a pistol like this to be biased toward positively locking open when empty even if that means not being able to use thumb pressure to release the slide. I'm fine with racking manually to reload.

I am disappointed that I've been left to sort this out myself. Seems like the troubleshooters or "gunsmiths" at S&W should be familiar with the feel of slide stops and be able to deal with this kind of thing when a customer sends in a pistol with reported weak slide locking. Apparently not.

Now I need to address the erratic ejection I've been having with this pistol. A few out of every 50 cases with 115 grain practice ammo have ejected over my head. When I tried some hot defensive ammo, cases ejected all over the place. There is a brass mark inside the ejection port where case mouths are hitting. Cases are ejecting at too low of an angle and hitting the slide, which then throws them in varying directions. My 1.0 Shield doesn't do this. Nor do any of my other pistols.

This page shows what I'm getting, but the small ejector face on the 9mm Shield isn't amenable to much tuning: Pistol Ejector Tuning Tips | An NRA Shooting Sports Journal

I haven't had any malfunctions yet from this, but it's a matter of time and isn't right or trustworthy. When test firing defensive loads I had a case hit me in my chest and land in my shirt pocket. Good thing it didn't decide to go for my eye.

The ejectors in my 1.0 and this Plus look and measure the same as best as I can measure. The extractor spring in the Plus feels much weaker than my 1.0, which I suspect is the root of the problem, though the extractor itself could also have some issues. I'll call S&W to ask if they'll sell me an extractor spring and extractor. If they are "factory installation only" parts like the slide stop was, I'll have to again pay scalper prices elsewhere.

This sure has been a lot of fuss to get a pistol running correctly, and it isn't there yet. Two trips back to the factory, plus buying parts and working on things myself. I was impressed with my 1.0 Shield, which is why I ended up with the Plus. After experiencing the lack of quality control in so many aspects, and the failure of S&W to make it right, I'll probably pass on buying other S&W pistols. If you happen to get a decent one, you're good. If you don't, you'd better be a gunsmith or willing to learn.