Hello gang,
Thought I would share my lessons learned from my first 308 build. I have to give 100% credit to this forum for making all my mistakes come to relatively happy repairs / changes. YOU GUYS ARE TRULY AWESOME. Remember, a lot of this I found from your site, was found AFTER being well under way to making mistakes. Like a lot of us learn the phrase "I don't know what I don't know"
So truth be told, I am an Engineer of many years, and am fortunate to believe in SOPWAMTOS, so the pole barn over the years has become nothing short of an antiquated but fully functional machine shop. I love the journey / process of building as much as the feeling of sending lead down range at sub MOA.
Part #1 - The 80% lower
Aw heck it can't be any harder than an AR-15 lower right...Boy did I learn the fun there! You have to scour the web, and do your homework, and look closely, as some of the models and drawings out there just plain don't add up! - nothing like the AR-15 drawings and CAD models floating around!!! - You guys knew that! - I looked, listened, and learned,
I made the jig, no different in design intent from an AR-15 lower. Sound approach, until I got a little cocky and over cut the front of the FCG well and broke out into the mag release spring pocket. My OCD is not happy with me, but my head says a 100 rounds later, it is still fine...Note to self, do the math and watch the dims from that mag release centerline to the front of the FCG pocket. You need that meat there. Turns out my model, was a good .157 too far forward. Rev B on those prints and models for the jig!
Part #2 Building the lower out
The lower was as some do, an 80% lower with a CMMG parts kit. Felt comfortable with them, as I have heard good reviews here and have had good luck in prior AR-15 projects. At this point I had NO CLUE what I was building when it came to that carbine buffer system out back 🙂 But everything went together like butter, and the hammer was positioned in the sweet spot as I was doing math to the BCA 308 upper I had in hand.
Part#3 Sending lead down range
Just to test function, I sent a few down range. Not happy, Failure to feed was random, and 100% no locking of the bolt, regardless of the mag I used. Remember I never bothered to look at the SHORT gas tube timing (15-3/16 gas tube), never bothered to look at the buffer length and weight (3-1/4 in - 3.8oz), never bothered to understand the spring they were using, never bothered to look at the undersized (.081 diameter) gas port drilling in the barrel. YEP thanks to you guys, as I started to send lead down range, hating the kick, and recognizing all the above...She got an overhaul YOUR ADVICE got me putting a rifle length buffer system, a new 15-1/2 gas tube, adjustable gas block, and opening up that barrel port!
Not perfectly happy with that port timing, as it is a bit long, but I have about .080 to bottoming out in the gas key. I have some 3/16 304 stainless, seamless tube that will be a project and post for another day. Not sure where BCA drilled that port at, but again, a learning for another day.
Part #4 The optics
I happen to have a Athlon Argos scope lying around from a bolt gun build, so I threw it on using a set of Vortex rings, 30mm up from the rail, on she went. Then the fun began when I learned all about "well would ya lookie there?", how do you grab the rear charging handle with the objective so far back? Not used to such a BIG LONG scope on an AR project...Hmmm... Then I start to realize that...wait I can't move it forward without the front ring being out on the hand guard...To the newbies out there...DON'T DO THIS:
Get a cantilever mount, and do it right!
So today I finally got out, and sent a good 100 rounds down range, after a little adjusting of the gas block, she is ejecting nicely and I am starting to zero her in!
Thank you to all on the forum, you ALL contribute to to our hobby / addictions / 2A rights!!!
