Avedis

From what I understand, there has been three. Blank (no stamp), S stamped near trigger return spring hole, and H, also stamped near trigger return spring hole. The H is the latest variation that I know of, The sear engagement loop or "candy cane" as people call it, has a more aggressive loop angle and subtle length changes. It engages sear sooner. It has slightly modified geometry so that contacts the slide stop for a more tactile "click" during reset. Here is a link to another thread with more info on the subject. If you take your slide off, you'll easily be able to see the stamp on the trigger bar. You can go on Brownells or G&R Tactical and order the correct one. If you can't find what you need, shoot me a message, and i'll see if I have an extra I can sell you.

The CAEK are a solid upgrade in that they remove almost all most of the grit in the trigger pull and clean up the break. The CAEK will have little affect on the pretravel, and you'd have to purchase an additional part (Action Enhancement Trigger body) to get rid of the factory hinged trigger design. To answer your question, which will improve it the most, the FSS is a pretty clear cut choice. It will do all the same things as the CAEK in that it will smooth/crisp the trigger up AND it will reduce almost all of the pretravel. Flat and curved are both great, they have the same internals. Apex is correct (of course), they are mutually exclusive. People were installing CAEK, DCAEK, AEK kits then months later trying to add the forward set sear trigger bodies to the kit. The issue is the FSS trigger bodies have different geometry, and wont work with the sear included in the AEK kits. It became such an issue that Apex had to stop selling the FSS trigger bodies as a stand alone product. https://www.twobrostactical.com/collections/m-p/products/m-p-forward-set-sear-flat-faced-trigger-kit-aluminum https://www.twobrostactical.com/collections/m-p/products/m-p-trigger-forward-set-sear-polymer-trigger-kit

Depending on the cleaner you're using in the ultrasonic, it may dry out the polymer frame. A few uses really wont damage much, but I can't see how it would be good to do it repeatedly. Everyone I have shown contact cleaner to has fully converted. Spray gun cleaner on frame, scrub with various brushes, spray clean with contact cleaner, lubricate as necessary.

One of the main M&P forums is MP-Pistol. That said, there isn't really anything on there that you couldn't learn here. There are a few guys on the mp-pistol forum that are pretty knowledgeable, but as a whole, Brian Enos Forum definitely tends to have more knowledgeable and experienced shooters.

The standard Apex sear that is included in the CAEK, DCAEK, ETC kits will not work in conjunction with the Flat Faced Trigger. This is because the lobe on the sear is not long enough. The flat faced trigger and forward set sear were made to work together. This compatibility issue has become so common that Apex has disabled the online checkout for this product (flat trigger only) on their website. You must call to order it. They are no longer selling it to their wholesale customers either. Full kit available here: https://www.twobrostactical.com/products/m-p-forward-set-sear-flat-faced-trigger-kit-aluminum

Speed Shooters / Springer Precision is the same magwell (springer manufacturers for them) I've seen both the ESP and Limited magwells out there https://www.twobrostactical.com/collections/m-p/products/m-p-esp-magwell https://www.twobrostactical.com/collections/m-p/products/m-p-limited-magwell

Springers have worked 100% for me https://www.twobrostactical.com/collections/m-p/products/m-p-140mm-extended-base-pad-6-select-color

5.11 Traverse are easily the lightest and most comfortable. Stretchy as well.

Trigger discipline is everything. I'm comfortable with 2.5lb, others may be 5.5lb. The good thing is, the springs that come with your gun, and the springs that come with your kit can be interchanged to make just about any desired trigger pull https://www.twobrostactical.com/collections/m-p/products/m-p-m2-0-forward-set-sear-flat-faced-trigger-kit-aluminum-fss

Apex trigger and your choice of sights: https://www.twobrostactical.com/collections/m-p/m-p-shield

LF Arms and 21st Century are no longer being made. Springer Precision is the only one currently being made (that I know of) https://www.twobrostactical.com/collections/m-p/products/extended-magazine-release-1 (free shipping)

.180 x 100, .180 x .110, .180 x .125, choose the width, but a 5" 2011 is pretty standard at .180 high. https://dawsonprecision.com/sti-fiber-optic-front-sights/ I believe the factory width is .125

I have both, The LF Arms is more slanted (gets bigger as it goes towards the muzzle) The Springer is more squared off, so the rear (chamber side) sticks out about the same as the front (muzzle side)

disregard

Production, no. Limited, yes. I haven't seen anyone do it though. Why not keep your factory slides as is and pick up one of the new performance center slide kits. https://www.twobrostactical.com/collections/m-p/products/m-p-performance-center-slide-kit-9mm

performance center slide kits in stock here: https://www.twobrostactical.com/collections/m-p/products/m-p-performance-center-slide-kit-9mm

If anyone is still looking for them, Two Brothers Tactical has 2 x 4.25" and 2 x 5" slide kits in stock. Free shipping as well. https://www.twobrostactical.com/collections/m-p/products/m-p-performance-center-slide-kit-9mm

Apex AEK is what you want. Fully polish everything and your'e good to go: https://www.twobrostactical.com/collections/m-p/products/m-p-competition-action-enhancement-caek

Apex AEK is what you want. Fully polish everything and your'e good to go: https://www.twobrostactical.com/collections/m-p/products/m-p-competition-action-enhancement-caek

As MPOM said, it is likely a timing issue. The gap on your trigger bar loop (candy cane) is opened too far. This allows the striker to be released prior to the striker block clearing. This robs the striker of a significant amount of energy, resulting in light primer strikers. To fix it, reduce the size of the gap on the trigger bar loop. This will fix your timing issue and allow the striker block to fully clear before the striker is released. If you have another M&P, that you know works fine, go dry fire it. It will make a crisp clicking/snapping when dry fired. A gun with incorrect timing will make more of a dull thud noise when dry fired (depending on how off the timing is). Essentially, you are doing the OPPOSITE of this:

What exactly did you install? FSS kit? CAEK? gotta be more specific so we can help diagnose the issue

Fairly easy to do with the right tools. If you don't feel comfortable doing it yourself, send it over to Two Brothers https://www.twobrostactical.com/collections/gunsmithing-services/products/sight-install

Can't go wrong with Dawson. Many prefer the blacked out rear w/ fiber optic front. Warren Tactical also has a great/similar set up.

10/17 or 10/15 will run fine