LMC (Low profile, duty, Magazine Catch) is a non-ambidextrous magazine catch for AR15/M16.
Note: LMC was not designed for large-frame ARs, do not use LMC on 308 ARs. The shorter shaft feature is designed with AR15/M16 width lower receivers in mind. The winterizing feature similarly only works on AR15/M16 lower receivers.
How much thought can one put into an AR15/M16 non-ambi mag catch? A lot.
LMC is based on the development of FCD’s EMR-A (Enhanced Magazine Release, Ambidextrous), and is centered around mitigating accidental/unintended magazine drops.
- 0.01″ longer catch (LMC’s 0.06″ vs. TDP’s 0.05″ length) that engages the magazine’s catch cutout window.
- Shorter (by 1 full turn of the magazine catch) shaft that lowers the installed height of TDP spec magazine release button on the right side of the lower.
- Winterized design to mitigate water pooling in wet and freezing temperatures.
- Billet machined in 4140, heat treated, black nitride coated.
- Proudly designed and made in the USA.
In 2018, FCD developed the LP (low profile) shaft option for EMR-A, which became standard on all EMR-A in late 2019. FCD also lengthened the EMR-A plate’s “ramp” section (the part that engages the magazine’s mag catch cutout/indentation). The LP shaft is designed to lower the installed height of the magazine release button (on the right side) so its top can sit slightly below the fence, while the longer ramp on the plate is designed to lengthen the magazine catch’s travel before a magazine is dropped. Both features are meant to mitigate accidental/unintentional magazine drops.
The “ramp” of the plate length is only 0.05″, a magazine catch only needs to travel over 0.05″ before a magazine is dropped. TDP spec M16 lower receivers, and semi-auto AR15 forged receivers based on TDP dimensions have a magazine release fence to prevent accidental/unintentional magazine drops. With a TDP spec magazine shaft and magazine release button, the top of the button is usually flush with the fence, FCD prefers the top of the button be lower than the fence. LPD plate’s ramp is 0.06″, the slightly lengthened ramp requires a longer mag catch travel before the magazine is dropped.
The very incremental increase of the catch’s length from 0.05 to 0.06 might beg the question, why not 0.07, 0.08, or 0.09? It’s important to maintain the balance in any system, it’s easy to reach the point of diminished or no return and cause unintended consequences. 0.01 increase is what FCD deems sufficient to do the job better without causing tolerance stacking with aftermarket magazines.
LPD shaft is one full turn of the mag catch, when a TDP spec magazine release button is fully and correctly installed (8 revolutions of the mag catch), the top of the mag release button is slightly below the fence.
FCD does not recommend blind hole magazine release buttons for defense and duty 5.56mm AR15s and M16s, or any extended magazine release with an even taller profile and over-the-fence protrusion. LMC is designed to work with, and lower TDP spec magazine release buttons (through hole), but is not made to address the flaws of other products. FCD has always had warning language for our blind hole magazine release button (EMR-HC), EMR-HC is perfect for thicker 308 lowers that require a longer magazine release button, but has a 0.08 protrusion over the magazine release fence on AR15 spec receivers. We moved EMR-HC to the 308 AR section to discourage 5.56mm AR customers from buying and using them on 5.56mm ARs.
LMC is a simple design, due to manufacturing delays, FCD has only been able to bring it to market in 2023. Between 2019 and 2023, they incorporated a new feature, LMC is now winterized. In freezing weather, TDP spec magazine catch can allow water to pool and freeze inside the cavity created by the magazine catch plate on the lower receiver, FCD made the plate thicker (the plate is now below the receiver, but protrudes slightly) which serves to reduce the area in which water can pool and freeze. It may not be a feature everyone needs, it is one of the ways we improved a near perfect TDP spec magazine catch.
Do note that water pooling patterns vary a great deal. LMC’s winterizing effort is focused on reduction, it’s not possible to entirely eliminate water pooling, the taller profile of the LMC.
LMC is shipped with a 10.9 inch/lb magazine catch spring. The 10.9in/lb magazine catch spring was first introduced in 2017, we had stiffer springs custom-made for our EMR-A (ambidextrous magazine catch). The 10.9 in/lb spring’s role is to offset the mechanical advantage afforded by EMR-A’s lever, it also has the direct result of making the right side magazine release button harder to press, which we view as a positive.
Note: LMC is designed for TDP spec M16s and AR15s. None of LMC’s features are beneficial on large frame AR style lower receivers. 308 AR spec mag catch shaft is longer, LMC’s is shorter than TDP spec in order to lower the magazine release button’s installed height. The winterized feature is wildly inconsistent on 308 ARs to the point of that feature being useless. The longer catch on the plate is lengthened from TDP spec, and doesn’t apply to 308 ARs. In short, do not use LMC on large frame, or 308 ARs.