Just some background: I’ve been dealing with AR-10s/SR-25s and copies for the better part of the past 20 years, in addition to AR-15s since the 1980s.
Reliability is really the top priority and pretty difficult to get dialed-in if you build. Heck, most manufacturers still have regular problems. Some of the best manufacturers had a lot of hiccups and road blocks along the way, especially the pioneers.
Jim Sullivan, who did the draft work scaling down the AR-15 from the AR-10 at ArmaLite in the late 1950s, said for some reasons they
could never figure out, the AR-10 was never as reliable as the AR-15, even though the daddy had a head start on the baby of several years.
After working on these things, competing with them, troubleshooting them, and trying to keep track of all the variations along the way of living through the new wave of large frame guns (that launched with the SR-25 in the late 1980s), I’ve taken quite a few notes on what seems to work and what doesn’t.
A general rule you might want to consider when taking the builder’s approach (the most prone to reliability and accuracy issues), is to source as many parts from a reputable company that has been building them and standing by them for a long time.
If you get a drop-in barrel from Company A, a BCG from Co. R, receivers from Co. D, gas tube from the usual sources, gas block from Amazon, buffer from here, spring from there, a 6061 RET, an LPK meant for AR-15s, etc. etc., it’s going to be a constant project just getting the parts replaced with ones that will function.
Since there is no TDP and industry standard for large frame guns, critical parts have been known to not fit so well together, and you get:
* Bolt lugs smashing into or shearing against extension teeth.
* Carrier rails smashing into RET boss threads in the lower, even when the correct buffer length, RET, and action spring are used.
* Gas rings that get shredded in poorly-machined bolt bores in the carrier
* Charge handles that don’t fit properly.
* Gas ports drilled too large
* Gas blocks too large for the journal for a loose slip-fit and insufficient gas seal
* Nitrided carrier keys that eat gas tube flanges
* YFS gas key fasteners
* Incorrect firing pin materials and hardness (tips break, cups form, primers get blanked or pierced)
* Incorrect gas system lengths (ArmaLite RLGS vs AR-15 RLGS with mismatched tubes)
* Bolt catches that break, especially when suppressed or with heavy buffers and large gas ports
* LPKs with AR-15 mag catches without enough threaded shaft for the mag release button
I could go on. Anyway, I really like to use as many parts from under the same roof from a great company.
The easy answer for a build is to go with the
LaRue large frame kit and keep as many of the parts homogenous as possible for your likes.
If you want another route for a super lightweight build, I would look at the 2A Xanthos receiver sets and work outwards from there.
For BCG designs and QC, I really like the ArmaLite BCG with the firing pin spring that prevents slam-fires, as well as the balanced lugs. I would look at that barrel extension match with maybe a Proof barrel. The chamber needs to be correct for a gas gun (more slop) with ideal leade location for magazine COL-limitations.
Find a quality steel gas block that won’t fit on without press-fit or thermo-fit, or very tight slip fit at the least. You really need to get the gas block alignment correct. Reputable manufacturers do this with different approaches, usually with set-up jigs with a press and a QC process to ensure alignment of the ports. Then the gas tube needs to be aligned as well with the stripped carrier in-position of rest in battery (inverted upper receiver does this).
I really like my feed ramps de-edged, blended, and polished.
I like my bolt worked over to remove sharp edges, chamfered and polished ejector(s), tuned extractor without sharp vampire corners, clean ejector channel, reduced length ejector spring, small diameter firing pin aperture (often call “high pressure” bolts, I think they’re closer to .068” vs .080” off the top of my head), and a carrier that doesn’t leak gas in the bolt tail hole.
The JP SCS recoil system is nice, and conventional set-ups require some knowledge about the differences with the large frame guns. You can have:
1. AR-15 Rifle RET, AR-10 rifle buffer (shorter than AR-15 rifle buffer), AR-10 rifle spring (longer, heavier weight than AR-15 rifle spring)
2. A5 or ArmaLite Mid-length RET, standard-length AR-15 carbine buffer (preferably heavier), AR-10 carbine spring (heavier weight)
3. AR-15 carbine RET, tiny little DPMS AP4 buffer, AR-10 carbine spring
You need to know what pivot pin and takedown pin diameters and lengths are needed for your particular receiver set. Again, same company who supplies their own LPKs is recommended (LaRue provides all of this with the UU kits.)
You’ll see a lot of people who slapped parts together, took some photos, shot some groups that are cherry-picked, with very low round counts from franked-10s, but things usually start to fall apart once you put a round count on them.
Just look at the threads with people who own some high-end AR-10s that are having issues, and then ask yourself, “Can I really do better than that when they have far more experience and specific tooling for this?"
If you like to tinker and learn, have at it.
If you need the rifle to work every time on your hog hunts, it might be prudent to get something factory or as much factory as possible.
I’ve seen plenty of guns that ran well for the first few hundred rounds, then just stopped. That’s pretty common in AR-10s.