These ABC/R are BLEM, The lower paddle's "butterfly" horizontal extensions are of different thickness. This doesn't affect most lowers, but on some, the left extension may need to be thinned/sanded down by 0.01.
ABC/R (Augmented Bolt Catch/Release) with its angled and larger top paddle and lower paddle with increased surface area, is purpose designed for use with AR15/M16 receivers equipped with ambidextrous magazine releases. Specifically, it is designed to address the difficulty with accessing the factory bolt catch's lower paddle with an ambidextrous magazine catch, such as Norgon's Ambi-Catch, on the receiver. Many of the ambidextrous mag release's lower paddle is on the same vertical plane as the factory bolt catch lower paddle, making identification difficult by feel, especially with a gloved hand. The ABC/R's chief effort is focused on that single issue. The lower paddle protrudes further, and is angled at 10 degree to give it even more surface area. These measures put the lower paddle and Ambi-Catch's paddle on different vertical planes. That done, we worked on the top paddle. While we don't use it ourselves, preferring to pull back on the charging handle instead to load and reload, we do recognize far more users use it, so the ABC/R's top paddle is made larger, and given a 5 degree angle at the lower 50%, and 10 degree angle at the upper 50% cant. The angled paddle makes it easier for the palm or thumb to access. The notch immediately above the ABC/R’s lower paddle isn’t there by accident. As you run your finger down the bolt catch towards the lower paddle, the notch is meant to provide tactile feedback to indicate the beginning of the lower paddle. It is important be able to differentiate one control surface from another, all without diverting one's gaze to it.
For 2020 ABC/R version 3 consists of the following changes:
* Ledge on top of the upper paddle, and bottom of the lower paddle to increase traction.
* Upper paddle options: FB (forward biased), standard (centered upper paddle), RB (rearward biased). * "Butterfly" lower paddle with increased surface area, while maintaining a healthy standoff distance from an ambidextrous magazine catch's lever. * Slightly lengthened magazine follower trip. Do note that the longer magazine follower trip is designed to make the bolt hold open after the last shot more reliable with more magazine varieties, but not meant to be a fix for out of spec receivers. We can lengthen it to a degree before running into unintended consequences by making the trip too long. ABC/R v3 FB (forward biased) and AA (dimpled) versions ETA: June of 2020. ABC/R v3 upper paddle options accommodate individual user's reloading technique. Upper paddle options include FB (forward biased), standard (centered, non-biased), and RB (rearward biased). FB (forward biased) is for right hand users that wrap their left hand around the magazine well, and use their left thumb to press the bolt catch's upper paddle. The FB version has the upper paddle shifted to the muzzle end to facilitate this reloading method. Standard (non-biased) upper paddle remains the same position as v1 and v2 ABC/R, its upper paddle isn't biased towards the front or rear. RB (rearward biased) is for left hand users that use their extended left index finger to access the bolt catch paddles. The RB version has the upper paddle shifted to the butt stock end to make the upper paddle more accessible. The "butterfly" lower paddle's horizontal extension increases the lower paddle's surface area, but stops short of reaching the bottom of the bolt catch in order to create a stand off distance between the extension and an ambidextrous magazine catch's lever. It is our opinion and observation that close proximity of two control surfaces is best avoided. The butterfly lower paddle has increased surface area, and doesn't interfere with an ambi mag catch's lever. Machined from billet 8620 alloy steel and heat treated with black nitrided finish. The ABC/R v3 is proudly designed and made in the USA. Starting from June 15, 2018, bolt catch roll pin, plunger and spring are included. Starting from June 15, 2018, bolt catch roll pin, plunger and spring are included. Please note the ABC/R are not designed for use on 9mm receivers that use Colt 9mm magazines which require a Colt 9mm bolt catch, or Armalite AR10B receivers.