Why Does My Upper Receiver Wiggle and Is This Common?
One of the great things about AR-15’s is that there exists a standard specification for the parts that allow interchangeability between hundreds of different manufactures. Each part that is Mil-spec is designed and built to a certain standard ensuring a proper fit between components.
In order for this to happen a certain allowable tolerance range exists and parts can fit on the tight side, loose side and everything in between.
The fact that your upper and lower receiver wobbles a bit does not mean anything is wrong with your rifle, it is in fact very normal and common for the AR style rifle.
Tips to Reduce Loose Fitting Receivers That Rattle
The AR-15 O-Ring Trick
One of the most popular methods to reduce a sloppy fit is to take a small o-ring and stretch it over the pivot/takedown lugs. This acts as a poor man’s shim and produces a tighter fit that will snug things up noticeably.
Although very cheap to do, you have to replace the o-rings nearly every time you remove your upper receiver. This is easy to do and worth a shot if you just cant stand a sloppy fit, I recommend these orings.
With that said this is not my preferred method as it feels a little too “redneck” for me, and can cause issues with rifle cycling properly. If this occurs you must remove the o-rings and try another method.
The Accu-Wedge
Many people love the Accu-Wedge since they last longer than the o-ring trick and do not cost a lot cash. It is a wedged piece of rubber that sits in the back on your lower receiver where the rear lug of your upper receiver sits.
This pushes the upper receiver up and forward to reduce or even eliminate any wiggle or wobble.
I know some people have to slightly trim the wedge in order for the takedown pin to be installed, although the fit should be tight to produce the best results.
There are knock-offs that do not last as long so be sure to get the higher quality versions like Brownell’s Accu-Wedge available for roughly $5. If you need to trim it start at the bottom rather than the top.
AR-15 Ear Plug Trick
This has been a preferred method to eliminate the wobble and rattle associated with loose upper and lower receivers. This is partly because it is effective and partly because most people have some ear plugs laying around. It is similar to the Accu-Wedge in that it works in the same way and is installed the same way.
All you have to do is position a spongy rubber ear plug in the back of your lower receiver where the upper receiver takedown lug sits. This puts your upper and lower receiver in tension making the fit tight which reduces or eliminates all wobble.
MicroFit Pins
Some of the previous solutions rely on applying pressure between your receivers, this does work well but can have some drawbacks. In some cases the gap between the upper and lower receiver (caused from the upward pressure of an o-ring for example) can cause the rifle to malfunction due to misalignment between the carrier to buffer.
JP Enterprises addresses the loose fit issue with some precision machined pins called MicroFit Pins. These replace your standard takedown pin to provide a tight tolerance fit between your receivers. There are three pin sizes available: undersized, standard, and oversized. To gauge the pin fit for your receivers, you can use standard takedown pin or use some gauge pins.
For the AR-15, Mil-spec pins are roughly equivalent to a .248″ gauge pin. Oversized and undersized MicroFit pins are offset slightly over .001″ larger or smaller. Oversized pins will remove much if not all of the slack in a loose receiver set while undersized pins will help with easier takedown of overly tight receivers with excess finish buildup.
Just know that the oversized pin will likely take the slop and wiggle out of your receivers it will also likely be more difficult to remove. Take a look at their website for more details.
Shimming Your AR-15 Receivers
This might be the best all around solution for your loose and wobbly receivers. Tempered stainless steel shims reduce play between the receiver halves for a tighter, smoother-functioning rifle without putting the two parts in upward compression like the orings/Accu-wedge/earplug tricks.
Upper and lower receiver shims fit on the pivot pin to reduce side-to-side play without making the removal of the takedown pin more difficult. If the wiggle in your AR-15 is causing your OCD to kick in high gear then the use of these shims are the best solution in my opinion.
Options to Consider Before Purchasing
If you are looking to buy or build an AR-15 you might want to select a manufacturer that offers a tight tolerance matching upper and lower receiver set that will fit perfectly with very little to no wobble.
Some manufactures like Aero Precision provide a tension set screw in the Gen2 lower receiver that allows you to adjust the fit to the upper receiver which means you do not need any o-rings or Accu-Wedges.
Most AR-15 owners just embrace the fact that some play between the receivers is normal however if you know this will bug you consider the options above before purchasing.
Is Accuracy Affected by a Wobbly Receiver Fit?
It is possible that a little bit of wiggle does not bother you, but maybe you are concerned that the wiggle is sacrificing some of your rifle’s accuracy. It is a valid concern. There is an intuitive belief that a tight fit between the upper and lower receivers is essential for accuracy and that a loose fit is bad. Many people have added their two cents to the topic both to why it does or does not affect your rifles accuracy. The good news is we do not have to rely on “bro-science” since there have been actual studies conducted on this topic may years ago.
The formal testing conducted by Rodman Laboratories looked at many different accuracy concerns and concluded that the bullet will have exited the muzzle of the rifle long before movement of the receivers produced a measurable effect. With that said, it is possible that the distraction of the wiggle could affect your shooting ability and therefor your ability to shoot accurately, but the wiggle itself will not be the direct cause of poor shots.
Conclusion
Receivers will normally exhibit a certain amount of looseness. This is normal and will not directly affect accuracy. Shooters may reduce the movement by insertion of a small amount of material between the receivers like stated above to improve the feel of the rifle, but it will not improve accuracy. It will however feel more stable and secure which for a lot of people, including myself, removes that little distraction allowing full concentration on your shooting.
Caligunner Copyright © 2024.
All Rights Reserved. Caligunner.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to amazon.com.