By the numbers,

Pull charging handle all the way back, and make sure face of bolt is forward of the ejection port back window edge by 1/16"~1/4", and lst inch of pull is no harder than middle of pull.

Look the mag ejection button, and is the end of the catch thread section, flush with the face of the button.


If no, then push button all the way in with pencil eraser, and thread catch one more wind in.  If catch threaded section is either a wind in, or wind out, then unthread mag catch from button, rotate button in recess 1/2 turn, and reinstall the catch.

Pull B/C from rifle, add CLP around the base of the key to top of carrier, hold the bolt in, and then use air compress to pressurized front of key 100lbs, and make sure not leaks between bottom of carrier key, to top of carrier.

Now with a piece of tubing on the end of the gas tube, CLP at the end of tube to FSB, and around front and back of FSB to barrel, same with 100lbs of air down the gas tube, to verify no leaks of these three areas.  Also, should have a good flow of air out the gas port to barrel bore, so listen for this as well, just in case gas block to barrel gas port is blocked, or the roll pin is missing that should be holding in the gas tube to FSB.

Now pull bolt off carrier, and dry fit the carrier to the upper, and when the front of carrier is about 1"off back of barrel extension, gas tube should be entering the carrier key cleaning, not causing the tube to bind when it enters key.  If tube is binding, then will need to pull front hard guards off barrel, so you can tweak the gas tube over the center of the barrel.

When putting the clean B/C back together, make sure to use CLP to lube the carrier inside and out.
Also, if mags have had some time to them, then pull then apart to CLP clean them inside and out.

As for barrel, CLP with chamber brush to scrub the chamber to remove any storage grease that may still be in the bore, then run dry patches from the chamber to muzzle, to get out all the fouled CLP.  Us Q-tip to clean the barrel extension area/lugs, and only lube the upper bearing surfices with CLP.

Not, do not use Hoppes gun solvent to clean the bore, since leaves behind a protective coating, that just turns into a gooey mess with it mixes with CLP.  So something like Sweets copper solvent to clean the bore with bore brush first, run patches until they no longer come out green, then CLP and chamber brush to clean chamber next, with the dry patched again from chamber to muzzle, to get the fouled CLP out.  Also, sweets leaves no protective coating behind, but even with you think you have the bore and chamber dry, enough CLP left on both for short term protective coating.

Simply, mag catch tight with threaded part to face of button, should hold the mags in well correctly to solve any low feed problems, and the rest is make sure rest of parts are clean/correct, and no gas leaks to cause short stroking problems.

If you still have problems, then get S&W on the phone, to look at the rig under warrenty.  Hence case being dented on loading, is caused by bolt over problems, with either the bolt not coming back far enough, or mag not recovering fast enough instead.

As for cases being dented on ejection buy the upper receiver deflector, kind of normal, but velcro on defector will solve that denting problems.

And again, face of bolt should not retract behind back of ejection window on full charging  handle pull, since if it is, then spent cases will ding off inside lip of rear ejection window, which can cause spent case to be pivoted back into action.

If you post a photo of the case dents, will tell of lot of how they are happening.

Is the gas key loose?

Is the buffer tube vent hole clear?

Bolt over rim jams, with either bolt not stroking back far enough to get behind rim,
Mag held low in the mag well, or mag not recovering fast enough to get top round tight against feed lips before bolt starts to move back forward,
Or wrong barrel extension type in play for upper receiver type, that is allowing the round to be correctly stripped out of the mag with the bolt behind the rim of the case, but nose of the bullet binding on entry instead.

Need to see actual jam conditions, and if bolt face is behind rim, or if bolt is under case in front of rim, or bolt on top of case past rim isntead.


Here we have bolt on top of case past rim,


Here we have bolt on bottom of case past the rim,


Here we have low feed into chamber, with bolt behind rim.

But case bent, and not allowing the bolt to fully lock up?

If yes, and not using the mag as either a by pod off the bench, or hand hold to cant the hell out of the mag in the well, then low feed out of the rig.

Remove the mag catch from the rig, strip the problem child mag down to just mag body, and with bolt closed, insert the mag into the well until you have the body feed lips tight against the bottom of the carrier, then look at the bolt catch channel on the non ejection side, to see where the mags slot for the bolt catch is against the bottom slot of the receiver catch channel.

Simply, mag locked in play, should have the mag lips about 1/8" below touching the mag, and if the mag is retained lower than this in the well, then going to have feed problem out of the mag with it sitting too low (or being able to rock too much fore and aft in the well during recoil).

It could be a problem with either the lower receiver with mag catch slot too low, or could be a problem with the upper receiver, with the B/C channel in it too high, but if you have another rig, then swap the mag catches between the two, to see if the problem is following the mag catch with it too loose in the catch slot/ it top ledge too low to retain the mag high enough.

Also, does not hurt to check a few mag slots against them selves, since on plastic mags, the top of slot for the catch to retain it, can peen over time.