Loose AR Receivers? JP Enterprises Fixed Them with MicroFit Pins

To me, the only major and glaring design issue behind the AR-15 and similar two-receiver designs is the interface between the two receivers. By using only two pins and having variable tolerance between them for mass-manufacturing inevitably leads to excessive slop. This is compounded by the choices in materials as steel rubs on aluminum receivers (but that is another issue entirely).

Various “solutions” to the issues have cropped up over the years to various degrees of success. The most prominent of them are the “wedge” and “screw” style tightening systems which put upward pressure on the rear lug. This works, but it does have its own set of issues and in extreme cases after wear, the weapon malfunctions as the alignment of the carrier to buffer is off.

In to provide a more neutral positioning solution is JP Enterprises. Rather than relying on various tensioning methods, JP has opted for a precision method with their new MicroFit pins. Basically, they are standard pins controlled to a tightly ground OD offered in various sizes to allow one to fit the pin to their gun. JP currently offers three sizes. Standard, under, and over, which are .001″ smaller and larger, respectively.

Knowing the fitment will be tighter, a recess is added to make it easy to get the pin out with a punch or bullet tip. All are polished and QPQ Nitride finished.

Pin sets are available for $28 or individual pins at $15, each. They can be purchased directly through JP Enterprises of JP’s dealer network. MicroFit pins are available for both the AR-15 and LR-308 platforms.





Nathan S.

One of TFB’s resident Jarheads, Nathan now works within the firearms industry. A consecutive Marine rifle and pistol expert, he enjoys local 3-gun, NFA, gunsmithing, MSR’s, & high-speed gear. Nathan has traveled to over 30 countries working with US DoD & foreign MoDs.

Nathan can be reached at Nathan.S@TheFirearmBlog.com

The above post is my opinion and does not reflect the views of any company or organization.


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  • Rick O’Shay

    So what do you do when your upper has a slightly smaller hole than the lower? Or a slightly larger hole? This seems to operate on the assumption that both upper and lower have the same size hole, and that it’s the pin that’s the issue. Unless I’m missing something here.

    • Gary Kirk

      Since the lower is the “firearm” you buy uppers that are <close in tolerance, then lap them out to fit precisely.. Never hand fit an AR, have you?

      • Gary Kirk

        K… Don’t know what’s up with my post?? Did not type it that way

        • BaconLovingInfidel

          Digital Tourette’s. Drink a shot of bourbon and spank your keyboard firmly once.

          All will be well.

          • Gary Kirk

            On phone.. Drank bourbon, chucked phone across room.. Will see if it works..

    • Kyle

      I don’t think these are made under that assumption. In a MIL-SPEC receiver set the pin holes are a minimum of .2500″ after anodizing. MIL-SPEC pins are .2482″, so at .001″ larger per the article, these pins will fit in any receiver set that is to MIL-SPEC standards.

    • Don

      Demon Tacticals Quick Pin

      • BaconLovingInfidel

        That’s pretty cool!

      • Greg Anderson

        Good luck finding the quick pin anywhere.

    • Bad Penguin

      Assuming hat both are not from the same manufacturer. Take your weapon to a competent gunsmith to drill out the small holes.

      • Rick O’Shay

        So get special pins, AND take it to a gunsmith to drill it out even more to make the holes match exactly? Eh. I can live with an accu-wedge.

        • Bad Penguin

          Whatever works you is good.

  • Andrew

    I certainly haven’t had much luck with the Aero Precision set screw in the lower method. For starters, you have to take the pistol grip off to adjust it which is annoying but then once you do, either it’s so tight that it’s really hard to get the pin to even move, or it’s so loose that it doesn’t make contact. Even if you do manage to get it to the sweet spot, it either walks its way out or wears down and you have to start all over.

    • CS

      Sig Sauer’s spring plunger “Accu-tensioner” has to be the best tensioning solution yet for the AR 15 platform. Alternatively, it would be nice to see a set of pistol like rails machined in to the upper and lower, so they slide apart like you’d disassemble your 9mm semi-auto.

      • Don

        Most of the high end AR manufactures have been using that tensioning screw for years, way before Sig even thought about making an AR style rifle. They also have added a tensioning screw in the lower that enables you to tighten up the stock trigger.

        • CS

          Actually, its not a screw. It’s a spring loaded detent, similar to the one found near the buffer tube.

      • BaconLovingInfidel

        That would be cool. I kind of assumed that was how they worked until I got my first AR.

  • Vhyrus

    Or.. you could not worry about the .005° of play in your AR since it has absolutely zero effect on your shooting…

    Just sayin.

    • Gary Kirk

      Barrel, sights, optic, and upper receiver.. All one unit together.. Funny how that works..

    • Dakota Raduenz

      I completely get where you are coming from, but when I see things designed to reduce wear- I think of our brothers and sisters behind the lines in California, Maryland, CT.

      They can’t buy a $50 lower to replace the old one like most of us can.

      • Christian Hedegaard-Schou

        Uh, yes we can.

        • Dakota Raduenz

          A. Which state (or Commonwealth, if you like)?
          B. For how long, and are you sure? My father didn’t realize the ammunition background check passed because in Cali so much gets buried..

          • Christian Hedegaard-Schou

            Californians can absolutely buy AR15 lower receivers and due to legal precedent, they cannot ban the sale of them in the future. They already did, and got knocked down by the court.

            They can pass whatever weird bans on features they want, but they cannot ban the sale of the receivers.

            They are currently on sale in close-to every gun shop in CA.

          • Dakota Raduenz

            This is good to know. But I did list 3 states.
            I may be wrong on all, and do stand corrected on California.

            But ease of business- I don’t have to worry about DROS, background checks (hello Armslist!), or anything else. Better to NOT have a ruined lower and not deal with stupid laws that shouldn’t exist.

            I know you guys catch a lot of flak for being in ban states, I wasn’t trying to go down that road- was just happy to see something that potentially makes life easier for you guys.

          • Bad Penguin

            I live in MD and the laws have gotten insane to try and stop the violence in Baltimore and the burbs of DC. Funny thing is most of the weapons banned or restricted aren’t ones the gang bangers use and murders are still sky high.

    • Klaus Von Schmitto

      Except when your trigger pins walks out of the hole.

      • Taylor Hardin

        which doesn’t happen on a correctly assembled firearm.

      • Bad Penguin

        Assuming you put a drop in trigger and didn’t tighten the set screws in the bottom. You could also buy trigger pins that have screws on the ends to prevent walk out.

    • The Brigadier

      No but stopping rattle is highly desirable. Springfield’s new Saint uses a nylon tightener that puts pressure on the rear lug, and it must be removed before you can do a complete field strip of your weapon. It absolutely makes the rifle quiet stopping the dangerous rattle and with a rattle free stock also, you can move through your landscapes like a ghost. If all you do is range shoot then don’t worry about it and rattle away. These oversize pins are another worthy solution to a very real problem. Rattles can get you killed and if the SHTF you want to be very quiet indeed.

    • Bad Penguin

      I have honestly had people claim it made no difference and they loved how easily the takedown pin and pivot pin would come out. Had to remind myself of some advice mom gave me as a kid “Don’t argue with stupid people.”

  • Mike N.

    The undersized pins would be useful for when the standard size ones are too tight. I have upper/lower combinations that require a Delrin punch to push out. The larger pins seem to be a solution in search of a problem.

  • Scott Wagner

    JP’s solution to tolerance stacking problems? MORE STACKING!

    • Kyle

      Standard MIL-SPEC tolerances allow for a minimum of a .003″ gap to a max of a .010″ gap between upper and lower. These pins actually reduce tolerance stacking as they remove a variable.

  • brutal

    A solution in search of a problem. Using a 90 cent Accu-Wedge is the cheapest, easiest, quickest reliable fix if you want to take any slop out of the upper to lower fitment and isn’t going to cause BCG buffer tube misalignment or wear issues. The Accu-Wedge is easier to assemble for a snug fit than an oversize pin and still allows tool-less disassembly.

  • Don

    This is a problem that has two perfect solutions that most people seem to ignore. Demon Tactical makes an adjustable pin called the Quick Pin that replaces the rear take down pin. There is zero movement when you use this pin. Then triggershims dot com has various thickness stainless steel shims that you use at the front take down pin. Again, another solution that offers zero movement between the upper and lower.

    • bobby_b

      Any idea where it’s available? I haven’t seen one for sale for a long time.

    • Wzrd

      Just a tip on shims- on one of my builds I put a shim on right side of upper pivot pin lug & it didn’t do much. Wasn’t room for one on each side. Moved it to left side & it completely eliminated the slop. So if using them try different combos & placement. Again, will work for some, not all.

  • mazkact

    The US Army Markmanship unit beds their rifles at the fit between the upper and lower. To seperate them one must pull both pins and remove the upper straight upwards. I’ve done some like this for Service rifle and it does make a difference. Belzona metal epoxy on the upper and lots of grease on the lower for a release agent.

    • Wow!

      I think it is placebo. The lower has no mechanical influence on POI POA relationship since the barrel and optic are mounted to the same upper receiver. Bedding only was needed in lock stock and barrel firearms, the last of which is the M24

      • mazkact

        Makes me shoot better scores. If it is a mind trick it worked.

        • Wow!

          Maczkact- I’m not discounting placebo. Shooting is mostly a mental game since firearms are inherently far more accurate than we are capable of matching. Its just that I feel like a lot of new shooters think they need it, when it is like a vertical grip, it is for comfort.

          Theother- That is a shooter error then. Every shot we fire should be tracked by your eye. If the POA moves as the shot is being made, we either don’t have a good stance or are flinching.

          One thing that has to be recognized is that when you hold a rifle and push it against your shoulder, you already take out all the slop in the rifle. Additionally, high speed photography has shown us that the bullet exits the barrel long before the recoil start moving the barrel.

      • TheOtherOtherMike

        It’s not about POI/POA, it’s about what happens to POA when stuff starts moving prior to bullet exit.

  • valorius

    I use an o-ring. A $.01 rock solid solution.

    • TheOtherOtherMike

      I use an O-ring as well, set vertically behind the front lug between it and the front of the magwell, the upper half gets smashed down by the front wall of the upper forming a something like a fat bottomed T out of the O-ring so to speak, this seems to provide some neutral centralization as well as forward and upward tension on the ass end of the upper and virtually eliminates slop, I also insert a washer-like shim on the right side of the rear lug when I close the action, though it’s a bit tricky to keep it aligned while closing the upper and getting the pin inserted. The idea of a rail system someone mentioned is pretty clever. I wouldn’t be surprised if that pops up from some company at some point.

      • valorius

        I go o-ring front and accuwedge rear. No slop whatsoever.

  • The_Champ

    When the Canadian forces upgraded their rifles to the C7A2, they included a little rubber wedge to snug up the fit. I have never personally seen them cause issues as the author claims.

  • Sking

    I have a S&W M&P 15, which doesn’t readily accept the accu wedge. So I used a hot glue gun, put a dab of glue onto the bottom of the upper, waited for it to cool enough, then closed them. It solved the slop.

    • The_Champ

      But $15 pin!

    • Wzrd

      You guys saying accu-wedges don’t fit do realize you trim them to fit, right? I’m not claiming they’re a miracle cure or that they’ll fix the slop on every gun, as I have used them- trimmed to fit -& they lessen the slop but don’t eliminate it. I just wanted to make sure you were aware of the trimming. Not trying to be a smart-ass.
      I do have one that was super thin to get it to fit. Almost nothing left. But I think it might’ve been my Mutant, so not milspec. & I guess they don’t inherently take care of lateral slop.
      Anyway I’m rambling. From my experience I can’t recommend them. Didn’t do much for me. Might fix problem for some but def not all.

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    • raz-0

      I’ve got a couple of mildly wobbly ars. None of them will fit an accuwedge.

      I’m not sure the JP fix will work either, but the accuwedge isn’t an answer for a lot of people.

      The accuwedge also won’t do jack to ease up the couple of REALLY tight upper lower combos I have.

  • Treyh007

    So what if you have an upper/lower that The rear pin won’t go all the way in……..

    • Christian Hedegaard-Schou

      Then your receiver extension is probably threaded in one thread too far.

  • Pilot

    Um. I just sprayed some Cerakote extra thick in the areas of the upper lug and in the lower where those lugs go. I covered the holes so the pins still slide in and out easy. But, with that extra bit of Cerakote, I have zero slop. It’s actually a little tight when I open my AR up. It was free since I was Cerakoting the gun anyway.

  • pun&gun

    Grammar nitpick: a “fitment” is a part or component. “Fit” is the word that describes how tightly parts are assembled together, hence “fit and finish” rather than “fitment and finish.” The two receivers and the takedown pins are fitments, the tightness of their assembly is the fit.

  • mazkact

    A cut and shaped piece Closed cell foam such as is found in a cheap flip-flop makes a nice “accuwedge”. I use them to create standoff when bedding an upper to a lower.

  • Amplified Heat

    Wouldn’t a pair of oversized pins and a reamer be a much better solution? I think this is a clever way for JP to offload their factory seconds at twice the price…

    • Kyle

      Factory seconds?