After 300 rounds, I'm noticing that the trigger has quite a long creep, a second very short creep, and then it is ready to fire. While it is consistent/predictable, this is not a great thing. Is it a common occurrence and if so - what are some effective corrections?
As noted, a fairly long first stage "take up" (not really creep) is normal for this gun. The second stage of this two stage trigger design has some challenges that will produce the characteristics you note.
Pulling the trigger pushes the trigger bar (TB) rearward. After travelling a certain distance without any engagement (a safety feature; first stage of a typical two stage combat trigger) the TB engages two different items:
1. The
sear, which will release the striker, and
2. The
striker block(SB), which blocks the striker from moving until the striker block is pushed upward. It is an additional internal safety.
The engagement surfaces of the stamped metal TB are rough. Until they are polished, you will get a gritty feel.
As well, the sear and striker block are not highly polished. The resulting engagement of these four surfaces is grittiness and extra pull weight because of friction.
This tends to dissipate somewhat after many many hundreds of trigger pulls (dry and live firing) as the parts slowly polish themselves from contact/friction. The trigger pull may actually lighten just a little as it gets somewhat smoother. This is a very slow, and for me frustrating process. I'm not very patient. I want my trigger to work right, right away.
The TB moves horizontally. The SB and the sear have to move vertically. Transforming horizontal movement to the vertical requires the surfaces to slide against each other for some (small) distance. If the four surfaces are not highly polished and at the optimum angles, you get a gritty, heavier trigger pull.
While S&W claims its standard M&P triggers are supposed to be ~6.5 (stage two, sear release), many seem to be coming through in the 8+ lb. range, and they are often gritty.
Apex makes replacement sears and striker blocks that are highly polished and have different dimensions and angles to greatly improve the M&P trigger system. However, polishing the TB engagement surfaces is still necessary, done by you. These changes will smooth out trigger pull sooner and better than waiting for the "firing polish". To lighten the pull lower than ~6.5 lbs. and/or change the trigger system engagement points (e.g., shorter first stage pull distance) requires different springs or other special parts (Apex).
If the Apex parts are not an option, you can achieve a vastly improved trigger feel by polishing all the mating surfaces, ensuring that the TB engages both the SB and the sear at the same time, and by enlarging and slightly rounding the SB engagement surface.
Here is a good guide to such work, although if you feel this is too challenging, a gunsmith should be able to do this quickly and not too expensively using just the parts in the gun.
http://www.burwellguns.com/misc/M&Ptriggerjob.pdf
Good luck. Congrats on your purchase of a very fine handgun.