Upper and Lower Receiver Mating Tolerances (STS)

[Pakin]

Hi everyone,

This my first post, but I just want to say I like how this site is organized and how I can search for information easily. I was on AR15.com, while the site was large, the search function and worth was limited (only searches last 30 days).

I just built my first AR-15, as well as my first personally own firearm. But I'm not completely new to rifles at all.

I used a Charles Daly Lower with a DPMS LPK mated to a Noveske N4 Midlength Upper Assembly.

An issue I ran into after putting the upper and lower together was that they were a little loose, moving mostly side to side. It is nice and tight up and down. It seems the movement is mostly isolated in the front pivot pin. However, the last time I fired an M4, I don't recall this detail.

There are some varying opinions I searched from normal to using something called an Accuwedge. I know there are manufacturing tolerance differences between two manufacturers, but I'd just like another opinion. Perhaps how movement/slack is too much?

Thanks!

[spamsammich]

Don't worry about it. Use the accuwedge as a target. Is this Pakin from PNWIC/NASIOC?

[Titleist]

Out of my 4 ARs only one is what I would call tight, i.e my LMT 16" piston gun, and even then you can wiggle the receivers a little bit.

I wouldn't worry about it. Even my high end SR-15 has some play. It functions fine. I was way too concerned about fit and finish at first myself, but even tight guns tend to loosen up with use.

[Pakin]

Cool, that is good to hear. Thanks guys!

spamsammich: Yes this is. Are you an NWIC'er as well?

[Stickman]

Hi everyone,

This my first post, but I just want to say I like how this site is organized and how I can search for information easily.

Perhaps how movement/slack is too much?

Thanks!



First and foremost, welcome to the board. It sounds like you made a good selection on your parts, which means your weapon should be both reliable and durable for a very long time.

The issue of upper to lower play is one that is largely a matter of personal preference. It does not effect accuracy, reliability, or any function of the weapon. I've got a carbine that is so loose I could slide a credit card between the receivers. I've got a couple that are so tight that I need to tap the pins out with a punch or something similar.

While working with military, and now withe LE issued weapons, I've found that there is a wide variance as well. None of it is a problem unless you start talking about massive rocking back and forth.

Tight pins are inconvenient, but create a solid feel. Loose pins are easy to take apart, but can bother some people.

[Pakin]

First and foremost, welcome to the board. It sounds like you made a good selection on your parts, which means your weapon should be both reliable and durable for a very long time.

The issue of upper to lower play is one that is largely a matter of personal preference. It does not effect accuracy, reliability, or any function of the weapon. I've got a carbine that is so loose I could slide a credit card between the receivers. I've got a couple that are so tight that I need to tap the pins out with a punch or something similar.


Thanks Stickman!

I actually tried sticking a credit card in between and it's a no-go. So I guess I shouldn't complain. :)

[Titleist]

My LMT/Larue SBR was solid as a rock, but has loosened up after about 400 rounds.

I can move the back of the upper of my SR-15 E3 IWS about the thickness of a fingernail, is it a little annoying? Sure, but when you're out moving and shooting you don't notice it at all, and the guns all cycle like a dream.

It's a trade off, you can have a gun like a FAL that's a ROCK but a nightmare to field strip, or an AR that's not always as solid but comes apart for easy field stripping.

[spamsammich]

spamsammich=supermarkus. Welcome aboard. Shoot the shit outta that gun!

[Fontaine]

Oh noes, another NWICer?

My member # is in the 30Ks, I'm one of the dumb asses that signed up for the forum with their real name.

[Eric]

It would take a substantial amount of play to actually create a problem. However, an Acuwedge will remove the play if you're so inclined. Instead of actually tightening the upper and lower, it forces the two apart. It's in interesting $5 gizmo, but some folks are worried that it will dislodge and end up in the FCG, which could render the weapon non-functional.

[Pakin]

Yeah, I don't think I'm going to touch it any further. It sounds like anything that takes up the slack will eventually wear down anyways. Thanks for all the reassurance.

spamsammish and Fontaine: Small world! I've been looking for an outdoor range (maybe I should have done that before I decided to build a rifle) to try this thing out, but the ones nearest to my area have the load-one-round-at-a-time rule or they are heavy into memberships. I found that there is a Ft. Lewis MWR Range that goes to 300, open to the public, and reasonable, but it's kinda far from me. Was hoping for something close in the Edmonds/Lynnwood area.

Happy 4th and keep a watch on the roof for flames!

[alt154shiver]

Not familiar with the NWIC forum, but I was stationed across the sound from you in Bremerton for a while. There are two ranges over in that area that are open to the public. Ten dollar range fee from what I remember, and good people too. Check out paulsbo sportsmans club and the Kitsap Rifle and Revolver club (I beleive gunsafety.org)

[spamsammich]

Yeah, I don't think I'm going to touch it any further. It sounds like anything that takes up the slack will eventually wear down anyways. Thanks for all the reassurance.

spamsammish and Fontaine: Small world! I've been looking for an outdoor range (maybe I should have done that before I decided to build a rifle) to try this thing out, but the ones nearest to my area have the load-one-round-at-a-time rule or they are heavy into memberships. I found that there is a Ft. Lewis MWR Range that goes to 300, open to the public, and reasonable, but it's kinda far from me. Was hoping for something close in the Edmonds/Lynnwood area.

Happy 4th and keep a watch on the roof for flames!

I've shot at Kenmore before, the only good thing is you get a good long function check when you shoot there. At least I know my bolt locks back every time i run dry. I still haven't found a good place close to Edmonds. I'm looking into several options. For now I get my rifles on paper at Sam's, then confirm anywhere I can find a longer range.