So, I tend to really notice the differences in my guns. Primary hunting rifle is a Rem. 700. 30-06. Noticed over the years, it loads and unloads like a dream. Great break on the trigger.
My newest rifle, Howa 1500 .243. Good trigger. Loads like Russian Dog. You gotta line up the rounds carefully, and they are hard to stuff in. (My fingers aren't fat, so don't get any ideas..... But it shoots flat; dang flat. I am not whining; I leave that to the coyotes.

Now, I have worked with AR's previously. They were always Colts, gov't issue. They each had their own quirk; the carbine was klunky, it had slop in it. The A2 was too damn heavy. Like carrying an underpowered m14 if you ask me.
So now, I have a relatively new S&W M&P 15 sport. Good rifle. The thing I notice?? The bolt slams home with some serious force. Like the buffer spring is hell bent on loading the round, no matter what. With no FA, I rather like it. Makes me pretty certain it is going to keep feeding ammo even if it got a bit dirty. The rifle feeds and ejects fine, so no issue. And, it feels fairly tight in the right places; does not feel like it's gonna come unhinged.
I was looking at a DPMS yesterday (There is a spot in the cabinet, so why not??) The bolt felt lighter than the M&P, for sure. Does not slam home with much authority. And, it felt a little sloppy in the hinge. Reminded me of the carbine I used to carry from time to time. In fact, it felt just like it, so I am bouncing it around in my mind. I will have dreams of patrolling a harbor at 2am looking for kooks jumping fences, trying to steal stuff from the small craft like anchors/ rope, radios, GPS, etc.

Do you notice certain things on your rifles, or do you just concentrate on the trigger, and let the rest go unnoticed?

My M&P 15 is almost 6 months old, has never had one glitch in its operation. What I notice most is when the mag is empty and it's time to reload..

I mostly notice how accurate my Sport is and that it has never malfunctioned. I also notice that it has a little play in the hinge, but probably less hinge play than a DPMS that I used to own. I don't consider it a problem. I've handled ARs in stores that have no wiggle between the upper and lower and some that rattle like crazy.

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JT

When I fired my M&P15 for the first time I was extremely pleased with how tight the action felt and sounded. I was used to M16a2s in the Marines that were wore out and rattled, so my M&P15 felt like a fine tuned ferrari. As noted above I to was impressed at the distinction of feel when the magazine was empty and the bolt locked back. Also I noticed how easy the pins holding the upper and receiver together pulled out, I expected it to be tighter and harder to pull out but my rifle seems to be tight with no problems.

I have a 9504 S&W pistol. Love the thing, have had it forever. One thing I notice compared to ALL other autoloaders I have owned???

All the little catch pins/ levers you need to semi-close when putting the slide back on after cleaning. If there was one flaw with this otherwise great pistol.......it's this!