I have noticed on my polymer framed guns my M&P 9 and the .40 I had the front rail section actually bent downward.. now that I got myself another Glock I noticed that my G19 front rail cups upward into the slide.. my p320 is pretty straight....anyone ever have issues with accuracy or anything?  I mean I don't use one but a laser mounted would be way off... I guess with a light it wouldnt matter as much... thoughts?

you are over thinking it, choot it.

What he said.

^ Ditto to what they said.

I've never noticed any bowing or bending on my polymer framed handguns.  Nor have I noticed it on my all metal ones.  Which is probably because ALL of them have Metal Top Slides.

Not an issue......

Thanks...
this is what I'm talking about... the glock front curves upward and contacts the slide, my M&P curves down in the front.. I got both used and they came that way...

I have OCD and I have just learned to ignore it. It affects nothing.

All my Glocks do that. Won't affect accuracy at all. Accuracy has more to do with the barrel lock up to the slide.

It may well have been molded and shipped straight. What can cause it to shift? It's polymer - take the slide off and you can see how it's easily moved up and down. Fiberglass filled nylon is not rigid, and it will bend. Can it take a set if constantly pressured one way or another? Some claim it's impossible, however,  it's glass filled nylon, not plastisteel composite. Two examples of note, when makers started molding pickup tool boxes from it, within months you could find them getting propped up in the middle with a concrete block to keep them from sagging under the weight. Owners report they could take them off and leave them empty in the driveway, they would take weeks of sitting in the hot august sun on concrete and wouldn't straighten out completely.

Next example, the Spyderco knives of the 90's, where even the clip was integrally molded. You can't buy those anymore, they changed to metal liners and steel clips. Why? Because, like mine, shoving them into a tight jeans pocket made the liners collapse onto the blade holding it in place with extra friction which made it doubly difficult to deploy. That is is the knife stayed in the pocket, as the clip would bow out and lose tension, causing the knife to drift up and fall out.

Polymer will bend and take a set. Holsters are the first and foremost cause of the dust covers bending and moving out of place, and yes, it would cause a laser to shift over time requiring repeated sighting in. A rail would beef it up but the attached light in a closely fitted holster could cause it to shift and over time remain out of alignment.

You want light inexpensive molded parts you get the negatives, too. For long term duty use I would attach nothing to a poly rail. In the day many questioned adding one to the 1911, and the maker of the most popular also sold a metal rail S&W riveted onto the 3 Gen TSW models. People criticized it, too - but now we have even weaker mounts cast into the plastic frames. If you can grab the mount and see the change in point of aim then expect that over time it will.

Rails with lights also prevent having closely fitted trigger guards as the light unit has to pass thru them, too, when unholstered. That means you don't get the same retention and some other method has to be used. Your choice, but all the follow on problems then keep getting more changes and the additive result is that you could install laser grips and and a red dot using a standard holster, of which there are far more choices.

Food for thought.

Excellent dissertation!

I have several Glocks and have noticed the curvature, or not, on the muzzle end of the frame. However, and although I do not have any scientific evidence to present, I believe the bend or curvature we see in the Glock polymer fame was caused at birth due to the injection molding process at the factory. On my Glock 19s the bend or curvature on the end is not all the same; some are curved more upward toward the slide and others are almost perfectly straight, with little or no bend/curvature. And, I believe the rigidity of the polymer frames are much tougher than you describe. I could be wrong, but I don't think the bend or curvature changes over time, although it may well flex a little with manipulation.

If you take you fingers and press the frame against the slide, there is enough play between the two so that they touch each other so as not to cause undue stress on the end of the polymer frame. Also, laser sights and, or light accessories attached to the end rail of the polymer frame may well shift and move over time with holstering and use, but the same would apply to metal frames with rails... at least in my opinion.

Just my unscientific .02.    

On GLOCKs it's called "pig nose". Absolutely does not matter.

Watch slow mo vids of poly handguns firing. The frames flex more than you think. Barrel to slide lockup is more critical anyways. 

FWIW my gen 3 G34 and my gen 4 G40 both do this, curve upwards slightly towards the front.

It did bug me at first, never noticed any upwards curve with my gen 4 G19. But every NIB Glock long slide I've looked at is the same. So I have to think it's on purpose.

I don't disagree that metal dust covers will also flex or even bend to a new angle. S&W was aware of it and added more material on the TSW models when they saw they needed it. It also created demand for a more rigid mount and within a few years both pistols came with integral rails machined in by their makers. The add on rails are now a rarity.

Anybody needs another example, just block up your big marine cooler on both ends and sit on it in the middle. It's instantly a trampoline. Poly isn't rigid - unlike metal - which can be good when you want it to delay the initial recoil over a longer time period, it makes a gun a softer shooter. Hang a large and heavy optic on that dust cover tho and it's going to bounce around. There is also the long term affect of that metal optic being clamped onto soft polymer and how it deforms the rail. Even the aluminum ones were noted for losing their finish - that's a few thousandths - and then some would tend to chatter into the material. I suspect that a laser/light clamped on tightly enough would leave teeth marks in it and need periodic tightening.

Those were big heavy inefficient units then, they are getting much smaller now, and eventually it will likely be of no concern. It's whether your gun and light combo in your holster has an issue - there are so many variations on that there is no one all encompassing answer. If you find you have a problem - then you do. May not even affect your buddy's gun.