So you have been thinking about building an AR and you keep hearing horror stories about how hard it is. Maybe even heard an ominous reference about a buffer retainer, before the story teller started sobbing hysterically, leaving you fearful of the day you would meet this fabled part. Well, my fellow freedom lovers, fear no more. For within the article you have begun lies the most common (and most easily avoidable) mistakes of the first time (or 3rd and 4th in the case of the slow learner) armorer.
You may have heard a story or two of a buffer retainer pin and/or spring going on a space-walk. As it turns out, this short little spring packs quite the punch and rightfully so. You see, the job of this spring is to keep enough upward pressure on the retainer pin that the buffer itself does not escape the confines of its tube. And if you’ve ever wondered just how much force the buffer spring exerts; just try locking the bolt to the rear, inserting your finger into the ejection port, and releasing the bolt. DISCLAIMER: please don’t actually do that. The good news is, the fix is simple and odds are that if you are building your own AR-15, you already have the correct tool. Drumroll please… a front sight tool (or any small socket driver that does not cover the entire buffer retainer pin. Simply place the tool over the pin while installing or removing the buffer tube and it will ensure that our escape artist of a pin stays put.
Drilling out large pilot holes in your lower is a great way to increase the life of your end mill, saving you both time and money in the long run. One issue that presents itself while using this technique is the rather common mistake of drilling all the way through your lower. An age old practice for machinists it to tape a bit at the proper stop depth. This trick isn’t all that great for repeated use as extremely sharp metal ribbons tend to cut away at it. A stop collar is an extremely economic and much more reliable alternative. Just be certain to recheck depth after every pilot hole to ensure that the stop collar hasn’t shifted.
Rushing; great for football, not so much for machining. Most tools that spin things at high rpm’s work best when you don’t use excessive force. Trying to hurry the process by forcing your tips through the lower is the number one source of premature failure in both the bits and the tools themselves. Going slow and using minimal force allows your tools and bits to function as they were intended and significantly adds to their longevity. Longer life = less money. Pretty simple math there.
All this talk about wear and tear on tools and bits brings us promptly to our next point. Using worn bits is the quickest way to ruin your day and your lower. You will end up with excessive flashing, tool tips will walk and result in misaligned cuts, and catastrophic failure can result in your bits and leave you with tiny shards of hot metal zipping through your tender flesh and into your eyes. So do us all, and yourself, a favor and start all your builds with sharp drill bits and examine your end mill for any chips or fractures in the flutes.
Conveniently enough, all three of our tool related issues are covered by the same answer: the Easy Jig tool kit for the 80% Arms Easy Jig. It contains all three drill bits recommended for use with the easy jig, an endmill custom made for the easy jig, and a stop collar for your material removal drill bit.
As for the last common issue, this one is purely a personal preference. Damaging the anodized finish. If you aren’t going to (Cerakote, Durakote, rattle can, dip) your lower and you paid extra to have it anodized, marring the finish during the build can be a peeve for those that like to admire their craftsmanship. For those of you that tie your gear to your bumper and drag it home along the scenic route, feel free to skip this. Lucky for we the few that like to keep our hardest working tools looking like they’ve never seen the outside of a safe, the fix here is simple and already sitting on your workbench. Masking tape goes a long way for reducing imprinting when you place your jig in a vise and tool marks during final assembly.
So, now that you’ve had the monsters evicted from your closet, get building.