Go / No-Go Gauges for USGI Magazines

Many of the weapon designers I have come to know well have very strong opinions on magazines. Outside of the suitability of one type (straight drop vs rocker) or staggered vs. single feed, they all universally agree that the weapon system is only as good as its magazines. It does not matter how well toleranced, machined, or timed a modern weapon is without good magazines that retain and present rounds to the action at the correct height, angle and pressure.

The AR-15/M-16 is no exception to this rule. While modern materials sciences have solved many issues for long-term storage, the military is well behind in the adoption of these materials (except the USMC, which went with the PMAG Gen 3 just a few weeks ago). Still, the military is notorious for using magazines well past their prime, either damaged from extended storage, misuse, and/or abuse. The old USGI magazines are typically beat to the dickens and back.
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Until just after 2010, there was not really much of a test to determine if the feed lips were unserviceable. But, back in 2011, the US Army created and fielded USGI Go/No-Go Gauges for measuring feed lip spread. These tools have become especially critical with the fielding of steel tipped M855A1, which spread feed lips can cause major damage to the firearm with rounds feeding incorrectly.

These can be picked up through Brownells for those interested from home. Retail is $59.99

Per the 82nd Airborne Division Small Arms Master Gunner:

NOTE: The NSN listed previously was the NSN for the magazine. The actual NSN for the feed lips tool is: NSN 5120-01-574-0036

Some people had questions from the feed lips tool post as to how much of a difference there was between a go and nogo. I’ve got one of the prototype tools present to give you an example of its use.

If you look in picture one, you will see the tool on the back side of a tan follower USGI magazine.

As you can see, the nogo side is the top side, if it stops before reaching the nogo side, the feed lips are within tolerance. There is a considerable difference between go and nogo.





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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  • Some Dude

    48 DOLLARS and 13 CENTS!!! No thanks.

    • Ron

      Only reason I bought one for my armory at work was it was on the government’s dime and I could justify it since I was buying something that would make sure the Marines’ weapons worked.

      • Audie Bakerson

        As an armorer I could maybe justify the cost, but as a user I might as well just replace 7 mags with brand new ones instead of testing them.

    • Tiru Maru

      Plus shipping….. 🙁

    • It was $60 when Soldier Systems made a post ?a few weeks? ago.

      • Some Dude

        The price in the picture is $48.13. Buy some glasses. Derp, derp, derp to you.

        • I was noting my error/laziness in a(n attempted) humorous manner.

          Hope it wasn’t taken as me being a jerk to others.

  • datimes

    I’d really like to have one of these designed to check out my MP-40 mags.

    • EdgyTrumpet

      Nice humble brag.

  • This device looks really nice and practical, but someone should let Brownell’s know their ad has a misprint on it. The price should read $4.81 each, but someone typed $48.13!

    Maybe that’s the government price so does anyone know what it really costs?

    • Sam

      NSN price is $53.27.

      • Drew Coleman

        How???

        • CNC machined from a quality steel, and then heat treated. Since it is a gauge I would bet that each one is checked for precision.

          This isn’t something that is cast, of MIMed.

          • Drew Coleman

            Still though, 50 dollars?

          • Don’t buy it. If you think $50 is expensive for a gauge then you aren’t in this product’s market segment.

            Go through Brownells or Midway gauge’s aren’t cheap. Because people expect them to be accurate.

          • some other joe

            How much is a good micrometer? There’s your other option.
            By way of comparison, how much is a M2 go/nogo gauge?

          • Sam

            NSN price $232.00. I know a lot of GM’s who used them as key rings.

          • some other joe

            It was a rhetorical question, but you make the point. Precision machined gauges hardened to keep their tolerances are more expensive than general purpose and tools. It is inherent in their standard of production.

          • Will

            I’m not sure the NSN price but it’s seems to be about $200. Plus they have to calibrated. I don’t know if this magazine tool would have to be as well.

          • darkdrifter

            GOOD Micrometer?? LOL! This thing is used to measure sheet metal feed lips. The go is .454″. No-go is .476″. That is a .022″ gap. A cheap set of calipers can do that with no issue. If you wanted a dedicated gage then you could buy a .454″ precision ground steel pin gage for $3. Then a .476″ one for $3 (Zz class pin gages are ground to within .0002″ of the nominal. Two ten-thousandths of an inch.. THREE BUCKS)… and a double end pin vise or Red/Green pin gage holder to hold them in if you want to be fancy. You still be $40 below Brownell’s price. With a round pin you could even engage any area of the feed lips you liked, or swipe the entire thing.

        • Sam

          NSN item is made at Picatinny Arsenal. Probably contracted through the army to a local shop. Add to the description of cost how much the shop time is to get precision work done.
          I don’t know who Brownell’s gets them from but I’d guess it’s the same contractor.
          In terms of cost, I have more than that in magazines but it is hard to justify a $50 gauge for a $10 mag. I’ve had problems from followers not lips.

      • I get it, I was just joking at the price. I know it is a gauge, and apparently well made, but the price is a bit much in my opinion.
        This doesn’t measure head space, bullet seating, cartridge length, or powder weight – things very important to the safe discharge of the round. It is simply showing whether the feed lips have bent too far out for the magazine to properly feed ammo. That’s important of course, but it would seem an accurate gauge could be built for much less. Perhaps instead of machined steel, use a hardened polymer. Just saying.

        • I don’t think there is a large enough market to go through the expense of injection molding a design such as this. And a CNC polymer gauge would probably cost much more than people are willing to pay. And then there are service life issues with polymer rubbing against metals.

          These are suitable for a particular user set, armorers that need to manage large amounts of magazines. Normal users, and gun smiths can probably get away with a set of digital calipers and accomplish the same task. Sure it takes longer, but they don’t need to measure magazine feed lips all that often.

          • I was debating on buying one, measuring then twisting and manipulating a stripper clip to do a similar task.

          • .45

            Maybe this is me being weird, but don’t most “normal” users, I.E. civilians, just keep on using mags until they are clearly damaged or start malfunctioning? I mean, my life does not depend on my mags working flawlessly, I can afford to find out on the range. The odds of ever having more than points riding on my mags are so low that the likelihood of a mag failure at that time is next to nonexistent.

  • .45

    $50? Hah! I has AK. I’ll use the feed lips to pry and smash things and AK won’t care! (I am referring to heavy duty metal ones. Screw those plastic things.)

    • anon

      nice meme

      • .45

        In truth though, the feed lips on a metal AK mag are considerably more durable than the mags shown above. I guess that’s what happens when you go Russian, instead of trying to go with disposable mags…

        TL;DR: Hah! AK is only!

        • PsL

          Steel Mags exist for the AR as well.
          Aluminum ones are cheaper for the military to buy and use than steel, weigh less, and last a considerably long time even with the abuse of training in different countries’ terrains – Portugal, Jordan, Kuwait, and Djibouti in my personal experience. The only mags I ever had issues with were old green follower mags from way before my time.

          • int19h

            It’s not just that AK mags are steel, it’s that they’re thick steel.

            Most AR steel mags have the same thickness as aluminum ones. HK and E-Landers are the only ones that I know that are noticeably thicker.

        • n0truscotsman

          Thats a fact. steel Warpac mags are near indestructable. I think the inherent design of AR mags keeps such a magazine design from being fielded. It really doesn’t matter now since polymer magazines and new generation of aluminums.

  • The magic of 3d printing, even if it only worked 100 checks would be insanely cheaper. That or machine one out of delrin.

    • Or just use a set of digital calipers, which IMO any gun owners with enough magazines to worry about this should own.

      • Tom Currie

        Which brings to obvious question: What are the width of the GO and NO-GO portions of this “not-a-gage” gage.

    • Will

      The problem is the material of 3D printing can be worn away with heavy use. By this being metal it means the life span of this equipment is greatly extended

  • Gus Butts

    I wish I had this in the military. Inspecting thousands of magazines in vaults would take seconds and not centuries.

  • jerry young

    $60 bucks is a lot of money when you can buy new 30 round mags for about $10 each, I try to keep a good supply on hand but does the average weekend shooter really need this? it’s not like most people are out there firing thousands of rounds off daily like the military, If you stick with metal mags and the feed lips become that worn you can tweak them a little to bring them back into specks, I buy only steel mags for my AR’s I find the difference in weight saved doesn’t outweigh the fact that no matter what plastic mags are made of plastic cracks and wears easier than metal, we have shooting classes and most of any feed problems I see are either a dirty gun or a plastic mag that has developed cracks

    • Jalen Byon

      This tool is designed for people who would have to choose between repurchasing hundreds or thousands of dollars worth of magazines every so often, or simply $48 once to drastically reduce how much they would have to replace.

      • jerry young

        Basically that’s what I said places like the military and ranges where they use lots of magazines but for the average guy it’s not a necessity but rather a wanted toy, it’s like go no go gauges for chambers unless you’re changing the bolt or barrel in say your AR there is no need

        • Jalen Byon

          You need to think this through. This gauge is made for groups that have hundreds or thousands of magazines to service and replace, not for the average shooter with a couple of magazines. Complaining that a tool for a completely different audience isn’t a good purchase is ridiculous. That’s like being annoyed that walk in commercial freezers are too large and expensive for a studio apartment.

          • jerry young

            Not complaining it was just a comment, if you want one there is no reason you can’t have one

  • Gary Kirk

    G.I. aluminum mag go no go gauge??

    Use mag till it starts to cause problems.
    Throw mag away
    Get new mag..