AR-15 Lower Receiver which Eliminates the Receiver Slack

The presence of slack between upper and lower receivers of AR-15 pattern rifles is sometimes considered a flaw of the design. Some people insist that it does affect the accuracy, others just find it annoying. In order to solve this problem, different manufacturers came up with various solutions. Perhaps the most known are the tensioning pins by JP Enterprises, but there are a couple of other products too (tensioning screws etc.).

A company called F&D Defense has a different approach in eliminating the wobbling of upper and lower receivers. They make a lower receiver which has a special contour (sort of a raised bump) which puts the required amount of tension to any upper receiver mounted on it. This system is called SHUT, which stands for Solid Hinge Upper Tensioning. Watch the video below to have a better idea of how that works:

Although it looks to solve the problem, the obvious drawback is that you have to buy a new lower receiver. In the case of tensioning pins, you just drop them in and you are good to go. Perhaps for a new precision rifle build it would be a good choice to get this receiver, because it seems to be a more solid way of removing the receiver slack problem. The question is … is it a problem at all?

The MSRP of F&D Defense AR-15 receiver with SHUT feature is $119.99.


F&D Defense HQ
Address: 201 W Oak, Seminole, Oklahoma 74868
Phone: 405-303-2403

Hrachya H

I was born and currently live in Armenia, where I work in a family business of leather goods manufacturing. Being a retired sergeant of my country’s armed forces and a lifelong firearms enthusiast, I always enjoy studying firearms design, technology and history. Also my knowledge of Russian allows me to translate and make Russian/Soviet/Combloc small arms related information available for the English speaking audience.
Should you need to contact me, feel free to shoot me a message at


  • France

    Step 1: Buy an AK
    Step 2: problem solved

    • noob

      and mount a wobbly rail on the top cover because soviet side rails are “weird”?

    • Elvis

      Step 3: Inherit unsolvable structural problems

  • Juggernaut

    I just use a few of the little black rubber bands from my kids’ Rainbow Loom and it snugs the upper and lower up pretty nicely

  • Step 1: Demand Mil-Spec then complain that your receiver has some play in it!
    Step 2: Redesign the lower receiver so that it does not wobble and is not Mil-Spec and might or might not fit your upper receiver.
    Step 3: Complain your new receiver does not fit Mil-Spec uppers and is too tight to push out the take down pins without a hammer.
    Step:4 Go to step 1.

    • TheNotoriousIUD

      Dont call me Shirley.

    • pun&gun

      I think a lot of people view “mil-spec” as a minimum, not necessarily a goal.

      • Well no AR15 receiver is mil spec to start with since they do not have the capability to accept M16 trigger groups. That aside, the specification is there to insure that parts can be swapped and will still fit without having to be modified. It is a specification and in this case sets a range of dimensions, aka tolerances, that need to be met to insure this. Having been involved in setting up manufacturing for AR15 receivers, I know that even if you hold minimum specifications to tighten up the receivers parts as much as possible there is still a little “wobble” in the connection.Manufacturers that sell matched sets that are tight together are not selling mil spec if they are tight.You can either have universal fitability with other mil spec parts or you can have custom fitted when interchangeability may be given up without fitting.

  • RickH

    Brilliant! How simple to make the lower receiver a bit too large so it binds and you have to squeeze the upper and lower together. I like oversized pins also, where I have to use a mallet to drive them in…..

  • TheNotoriousIUD

    Making something too big doesnt mean that it “fits”.

    • noob

      That’s what she said!

  • Sunshine_Shooter

    There is a third group of people you failed to mention in the first paragraph: The people who don’t care about the little bit of play between the receivers and find such complaints childish and nit-picky.

    • Porty1119

      Seriously, this. The entire sighting system is contained in the upper. Upper-lower play doesn’t affect accuracy on any meaningful level- nobody uses an AR as a technical benchrest gun.

      • Quest

        Uhm ive seen it in the 1000yard milkjug challenge. Even hitting with crap ammo (= the accuracy diffrence of the ammo is dozend times larger than this receiver thingy)

  • Christian Hedegaard-Schou

    “Perhaps the most known are the tensioning pins by JP Enterprises”

    If those are the most known, Accu-Wedge would like to have a word with you.

    • Scott Wagner

      Accu-wedge probably didn’t want to bid on the ad space.

  • Rick O’Shay

    Play between the upper and lower? And HOW, pray tell, does that affect accuracy? It certainly doesn’t affect accuracy to any degree that 99.9999% of us opr8rs will ever notice.
    It strikes me as complaining for the sake of complaining.

    • Tacticool

      0p3r8rs you casual

    • TheNotoriousIUD

      In Cali they just weld them together.

    • thedarkknightreturns

      A little play isn’t a huge issue, however a gap between the upper and lower right in front of the receiver extension is a problem. If the fit isn’t proper there the gun will recoil on the take-down pins.

      • Rick O’Shay

        Okay, but that still isn’t telling me how that affects accuracy.

  • Daniel

    Great to hear of another possibly great product from F&D. Just don’t mention them over on Snipers Hide…..

    • Drew

      LMT has been doing this for years. They put the bump on the upper and i think only ont the large frame.

  • Midwest Marco

    Sig has a nice spring loaded pin called an “Accu-Tensioner” in their AR pattern rifles. The M400, Sig 516 and 716 have ’em. No wobble between the upper and lower

    • CS

      I agree, sig’s solution is probably one of the best.

  • Jim Page

    Sure wish something like that was made for the FAL.

  • MrBrassporkchop

    Just do what I do and smash a taco between the upper and lower.

    Does wonders.

    • LGonDISQUS

      I thought a weekend of smashing tacos is what you do on a weekend of shore leave, when you take a trip to Tijuana?

  • To Tin Fung

    calm down guys lol. i think this is just looking at the problem from a machine design point of view. some machinist picked up the gun and said: i think i can reduce the clearance and did that.

  • I’m a fan of Aero Precision’s nylon tensioning screw on the grip mounting block; completely hidden and fully adjustable so it’s 100% universal for any upper.

  • anonymous

    “The presence of slack between upper and lower receivers of AR-15 pattern rifles is sometimes considered a flaw of the design.”

    If the fit between an AR-15 upper receiver and lower receiver needed to
    be tighter, John Browning would have designed it that way…

    • Major Tom

      John Moses Browning did not design the AR-15 family.

      • 22winmag

        I think that was meant to be tongue-in-cheek humor.

        The OPs statement “John Browning would have designed it that way” was not a conclusive statement that John was in fact, the original designer.

      • ActionPhysicalMan

        It was a joke.

  • noob

    Which marketing goon made the slogan “mil-spec ar-15 lowers with the tightest fit of any build” and not “If it ain’t SHUT, it ain’t another-four-letter-word-beginning-with-S”?

    • Major Tom


  • noob

    They say that if you hear noises in your house at night, just rattling the upper receiver against the lower receiver of your AR will scare the thieves away.

  • Bradley

    Whether it’s a problem or not, in my opinion, depends on the severity. Yes some just barely wiggle if you intentionally grab them and put force on them each way, but some are just ridiculous. I have a rifle with mismatched brand upper and lower that just has a slight amount of movement. I’ve seen some colt, and other factory rifles, that flopped around with the slightest movement.

  • Bob Barkertor


  • 22winmag

    Why not just a few strips of electrical tape?

  • valorius

    O rings- $.02 cents, problem solved.

    • Sunshine_Shooter

      $ .02 cents? Is it dollars, or cents?

      • valorius


  • USMC03Vet

    I hear switching to aftermarket trigger guards reduces moa by 1 too.

    • LGonDISQUS

      I thought upgraded trigger guards were like Charlie and the a Chocolate Factory Golden Tickets nto SOF training positions?

  • Or, you could just buy a receiver like the Aero Precision one that’s much, much cheaper and uses a set screw to tension the upper.

  • Tom

    All these solutions push the receives apart.. Instead of squeezing them together..

  • TC

    ‘Tension’ refers to a pulling force. The proper term for these methods of eliminating the play in an AR receiver would be ‘compression’. These actually push the upper receiver away from the lower.

    • 22winmag

      Never spoil a good story with proper word usage, good grammar, or the facts.

    • Laserbait

      Actually, it’s compression between the upper receiver and the humps that produces tension on the pins.