How does the grip pressure affect ejection?
Frame stability (against movement), as well as slide velocity and travel during the recoil cycle.
Is this common with other auto's?
Yes, but it generally seems to be more often encountered when folks are using polymer-framed pistols.
Folks with less experience shooting semiauto pistols, or at least shooting polymer-framed pistols, seem to report this sort of thing more often than more accomplished, experienced pistol shooters, upon occasion.
It's not an uncommon thing for an instructor or armorer to check for when such functioning problems are experienced by shooters.
The M&P armorer manual, for example, discussing a Failure to Eject (including Stove Pipes) problem has as one of the probable causes listed "shooter induced". The recommendation is to evaluate and correct, but in the class it's recommended to check the shooter's technique for grip/wrist issues.
In the Sig armorer manual, under Stoppages, Malfunctions and Their Corrections, it lists "Shooter error/Keep wrist locked and maintain a firm grip when firing the pistol" as one of the potential corrections to the following problems:
Slide does not close completely
Double Feed
Inconsistent ejection (including trapping brass in ejection port)
In the Glock armorer manual, "Shooting with an unlocked wrist" is listed as one of the probable causes of the following problems:
Failure to extract
Failure to eject or erratic ejection (incl stove pipes)
Failure to feed
Slide fails to lock open on last round
Failure to fire
I could go on, but you get the point.
I haven't heard of any recent issues involving gun-related extraction problems since the Pro model was released. I heard of some very early production slide & extraction issues of a limited nature back when the M&P was first released.
Since the M&P extractor is technically considered a fitted part I suppose an occasional, odd extractor might have been fitted a bit too loose or too tight, or an extractor spring might be slightly out-of-spec (we ask a lot of rather inexpensive, small mass produced springs, you know). Although not heard of often in new guns, it's also possible for an occasional part to be defective or damaged (extractor).
This is where S&W's lifetime warranty and free round-trip insured shipping is something to be appreciated.
FWIW, ammunition produced on the low-power end of the normal range can affect functioning at times. Take into consideration the normal deviation to be expected when ammunition, especially low-cost ammunition, is selected for use, too.
Also, it's not exactly uncommon to hear someone report that budget/low cost 115gr 9mm ammunition has been connected with some occasional complaints of feeding, extraction & ejection in some new pistols. I can make a G26 exhibit erratic ejection issues much more easily when shooting standard 115gr 'training/practice' loads than when shooting 147gr 'training/practice' loads because of the recoil impulse ... in my hands, using my G26.
I can't get the same G26 to exhibit the same ejection issues at all when using +P/+P+ loads.
Just my thoughts.
Why not call back and ask to speak to a customer service person at S&W about your experience and concern?
