tight fit or too lose what we are talking is the spec we are talking tolerances and tolerance stacking.Uppers and lowers are made plus or minus within the spec so sometimes you get two parts at say the high end of the spec and there too tight...it happens inspec and out of spec and mil spec are used and misused so much it makes my head spin.

That's beauty of it. We make our AR's so that WE like the way they feel to OURSELVES.

Does it really matter if your buddy approves or not? I like my gun tight. I use an o-ring on the lug. Problem solved.

Yup, the orange barrel style for me.

about a thousand rounds later and probably 20-25 on and off for upper changes and when i go shooting i separate because i haven't had room in my rifle case(the 10/22 and ak ride in there).   the paint trick is still locked solid.

Or they make shims for the slop. Takes it right out of the upper/lower fit

AR15 manufacturers hate him for telling shooters this one weird trick to remove sloppy fit ...

 Interesting.  This is a bit off topic, but I get the impression the US Army is more enlightened these days about maintaining accuracy after initial zero.  When I went through BCT at Ft Ord in the Fall of 1961, we were issued beater M1 Garands.  After every day at the range, a total of about a week, we had to clean our rifles with hot soapy water, running segmented cleaning rods back and forth from the muzzle.  

In those days, qualification was via a modified National Match course, known distances with spotters in the pits and maximum range being prone slow fire at 550 meters.  I barely qualified marksman.  I was so ashamed I never wore the metal.  Later in my permanent unit, 2nd BG, 28th Infantry, we got brand new M14s from Springfield Armory (the one in Massachusetts).  I qualified expert on pop up targets at unknown distances ranging to about 350 meters.  I believe that same or similar qualification course is still used by Army troopers. - CW

i just thought i would offer an update because so many said my trick wouldnt work or wouldnt last. both my uppers i have built are flattop blems. one was sloppy beyond practical use. the problem i see with an accuwedge is the shipping will cost more than the product. And I had flat paint laying around.

Because $4.45 shipped for 3 of them is so much money. It almost costs as much as a can of paint. Here

Which is a GOOD thing.

 
Tight fit between upper and lower is not desireable.

Franklin Armory mills the lower to have a set screw where the Accu wedge would drop it.  Seemed like a cool addition they mill into the lowers they sell.

http://www.franklinarmory.com/PRODUCTS_Stripped-Lower.html

I am using this lower on my build.  They are local to me and I wanted to stimulate the local economy.

Do what you want.

Those who think the upper loses accuracy have yet to explain it, tho. If the sights are on the upper - ok Barrel moves, sights move, sight alignment hasn't changed. The hammer to firing pin alignment did, tho. So how does a minute change in the hammer face striking the back of the firing pin change accuracy? That is the ONLY change -

I will tighten up my new AR pistol build for one reason - it's for hunting, and any noise in the field out of the ordinary could spook a deer in close proximity. I did carry a GM Hydramatic that did that in basic, but with all of the other gear and 30 other guys, one rifle making a ticking noise irregularly isn't a big deal. 60 stomping boots kicking thru the forest floor is. With me still hunting slowly, the potential noisemaking ability of a loose fit might ruin an opportunity. Applying that concept goes even further - free floats ringing like little dinner bells every time a branch hits them isn't good either. So, no free float. I made that mistake on my 6.8 - it's a constant hassle stalking in dense cover.

But worrying about a loose fit hampering accuracy? Depends on the barrel first. If it's milspec, it's a 2MOA gun, no grounds to complain. If it's a .5 MOA gun with handloads, whatever. Do consider, tho, that slinging up will pressure that accuwedge and the upper will move in relationship to the lower. It's NOT a metal to metal fit, it's metal on polymer, and exerting pressure means it will deform, and the upper will change relationship to the lower.

That darn hammer is going to move to one side of the firing pin and mess up your group anyway.

Seems odd that some would get their shorts in a wad over an issue like this.  Since the consensus seems to be that there's no critical need to "tighten up" the clearance between the upper/lower, it also seems to be the consensus that there's no problem with snugging up that clearance with an appropriate method.  Which begs the question...can't each side of this argument just move on to the "what motor oil is best" argument?

Most AR / Mil. Spec. take down pins mic. at or near .248" to .2485" Dia.,  Armalite  had a one time made National Match pins that were right at .250", The .001" to .002" thousands in size will take most of the play / looseness out of a quality receiver set. (can't do much for the ones machined way out of tolerance) I keep a few sets in my parts bins at all times and when things get loose I switch to a large pin. Armalite front pin number is ENM001 rear pin ENM002 last order I placed they were $10.00 a piece. They work well to restore and give that solid feel.

I ended up with an Armalite NM pivot pin and a normal takedown pin in my first build. Prior to that I had picked up a few uppers and tried to it and match other pins and upper/lower combos to get a great fit.
My noveske gen2 build was much simpler. Just add vltor.
Yes, I probably but too much thought into this. My builds do feel quite solid and I'm fine with that.

Here's my take on the value of tightening up the lower to upper fit:


Think about what you do when aiming the rifle... you do use your pistol grip and stock as part of your aiming, especially so if shooting off of a bipod.  So if your upper to lower fit is very loose then the translation of your pistol grip hand movements to the position of the upper, and of course where the barrel is aiming, will not be a 1 to 1 translation.  It's like driving a car with old worn out bushings in the steering/suspension system, you turn the wheel but the car reaction is a bit sloppy and delayed compared to the motion of the steering wheel.  Of course this is a very minor effect, but slight movements of the weapon are amplified at longer ranges.  It's true that all the accuracy comes from the components of the upper, but the ability to align the upper using the parts connected to the lower without having to compensate for a sloppy fit between them has some value in my opinion.  If fitment really bothers you get a matched billet upper lower set with a built-in fitment adjustment screw, like a Spikes Tactical Billet Lower Gen 2, or a Mega Arms Billet set.  

While it's probably not necessary to be tight, I agree with those that if you're into precision shooting, you may find it will help if it is tight.  

But beyond that, I've seen ones be so bad it's annoying.  Like you could fit a sammich through the opening.  OK, maybe not that bad but it can be distracting and irritating.  While you shoulder it you can move the upper back and forth a bit.  That's just dumb.  


I've also had some be so tight they won't go together.  I've had friends that have had that problem too.  And one time I have an upper that like was off centered on the lower that it was hanging over one side a little too much.  I just played musical lowers to find a better fit.  


I think trying to get a good fit is a good thing.  I think too loose or too tight could potentially cause some problems.  Possibly.  Sometimes too tight could mean your mag might just be a hair too tight on the bcg and maybe slow some things down.  Or too loose could possibly affect accuracy and if bad enough maybe affect feeding also.  Not sure if there's ever been any that bad.


Anyways.....