Loose AR15 Receivers, How to tighten AR15 upper.
AR15AccuShim.com
A15 wobble, How to tighten upper lower receivers

Questions and Answers...
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When should a shim be installed?
When receiver play/wobble is noticeable it's time to install a shim or while the price is right and the getting is good have a kit on hand for days ahead. Solid mounted free float handguards, barrel weight, scope weight and fixed stocks can make receiver play more noticeable. Lightweight rifles with two piece handguards and adjustable stocks can make receiver play less noticeable. Various thickness automotive feeler gauges can be used to determine exact play.
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What is the difference between the AccuShim and NM Shim?
The only difference is one is stamped AS and the other NM.
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How much is too much receiver play?
Generally if an AR15AccuShim cannot tighten receivers there is too much play for installing expensive barrels, triggers, etc. The shim is designed not to tighten receivers with excessive wear or with machining issues such as too much recess/sear relief depth, incorrect pin bore locations, etc. Since play between quality competition matched receivers is zero the play between average interchangeable commercial receivers has a competitive limit.
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Can  the shim be purchased separately, etc? 
The shim is available only in a kit complete with hardware and installation instructions. Due to postage cost the quantity dropdown menu is limited to 3 Kits. We also offer a Gun Store 9 Pack that includes USPS Priority Shipping.
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How long does it take to install the shim?
Surfacing time varies according to receiver play. Average first time installation time for a rifle is 30-45 minutes. Generally installation time for a second rifle will be considerably less.
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What about an AccuWedge, etc?
If you have an unloaded rifle with an AccuWedge installed hold the upper receiver and lower receiver and twist. If the receivers have side to side movement along the seams means the receivers are not tight and right. A pliable AccuWedge pushes up against the takedown pin lug and acts as a pivot point. To tighten receivers requires precise pin bore size and locations like those found on quality Matched Receivers. To tighten most interchangeable commercial receivers the space between the receiver sides has to be filled which allows the takedown pin to pull the halves together. An AR15AccuShim aligns the receivers and provides rock solid side to side support without altering the original takedown pin configuration. O-rings, epoxy, tape, ear plugs, inserting a loaded mag to remove play and other such remedies are not recommended however some are better than doing nothing. Before purchasing a rifle equipped with an AccuWedge remove the AccuWedge and gauge receiver play.
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What can be done if the recess/sear relief measures too deep?
This usually happens with unknown brand receivers or blems that were not machined mil-spec in the area of the sear relief. The only remedy is to gauge or inquire about the relief depth before purchasing an unknown brand or purchase a known brand receiver such as Aero Precision, Anderson, Spikes, etc. There is less chance of purchasing a lemon when receivers are in sealed factory packaging. 
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Will the shim tighten .308 upper receivers?
The shim does tighten .308 receivers that have the AR15 upper receiver recess/sear relief dimensions shown on the Installation Basics Page.
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What can be done if the receivers and shim loosen, etc? 
If the receivers loosen over time first measure the pins. If pin diameter is under .248" try replacing it. There are also oversize pins available from JPRifles.com. If pins and bores check use End Nipper Pliers to carefully pinch the center of the shim leg lengthwise along the side. Squeezing the straight side portion thickens the shim leg a few thousandths, check progress with a caliper. Any tool that can compress the legs evenly can be used. 
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Is the Shim for an Assault Rifle?
A question connected to "Assault Rifle" is most probably the result of gun control propaganda. People who wave the gun control flag assume they are doing something honorable. What they don't know is the Roots Of Gun Control are in racism, genocide, etc. The history of Gun Control isn't pretty. With media help certain Gun Control Fanatics who have 24/7 Armed Guard Protection intentionally misuse "Assault Rifle" to demonize millions of responsible citizens and to drum up support for gun bans, restrictions, etc.  The AR in AR15 does not mean Assault Rifle or Automatic Rifle, AR means, "Armalite Rifle." Our shim occupies the sear relief and would prevent a Pentagon Defined Assault Rifle from firing, etc. The question is, Where will Gun Control Fanatics be to help should you and yours be cornered by a criminal? The answer is where Gun Control Fanatics always are...Nowhere.

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Can an Accuwedge be installed with the shim?
Yes it can, we've used both together.
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How does the shim work?
The shim aligns and stabilizes the receivers much like cardboard works beneath a table leg to prevent wobbling. To tighten receivers there are factors to consider such as the takedown pin lug bore in most upper receivers may appear round however it is slightly elongated to form a slot. Because the upper receiver takedown pin bore is a slot there is no significant front and back contact with the takedown pin. Also there is no significant up or down force during recoil at the caboose end of the receivers. Basically all the takedown pin has to do is prevent the two halves from opening. Because the upper and lower receiver pivot pin bores are round they work the hardest and receive most of the abuse. Abuse increases when the receivers are loose and misaligned, abuse decreases when the receivers are in alignment between shots.
When the receivers are closed the curve portion of the shim is suspended above the opening in the lower receiver. The important opening in the lower receiver allows the shim legs to work independently. The opening between the machined sear relief in the upper receiver must remain open due to dropping the charge handle nose into the opening during quick removal, etc. The shim had to be enclosed and made from a material that is compatible with Aluminum. The material could not lose tension or break when twisted and bent numerous times, etc. Getting the shim to work without permanently interfering with the design of Eugene Stoner et al was also a factor.
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What tools are needed to assemble a rifle?
The tool to start with is a single or dual scale Dial Caliper. When properly assembling these rifles everything gets checked, measured, gauged, fitted, aligned, etc. Assembly tools are available from Brownells, Fulton Armory, eBay sellers, etc. Videos showing tools and assembly are available. Visiting a Gunsmith who specializes in the AR Platform may be the best source for a tool list and for what to do and what not to do. For the same model general purpose calipers we've used for years enter 332568970700 in eBay Search.
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