y
I was thinking if fitting parts were necessary like when working on a M1911a1.
Nope, Stoner held specs tightly enough that parts from two different makers 1000 miles apart should fit. Mine do.
There are a few finesse points - makers can and do measure their parts and sort them into batches so compatible assembly with other parts works out with the stack of tolerances in an acceptable range. We don't - we've got just the one part and live with it.
So, the upper and lower might have very tight or loose fits when pinned together. The maker matched them, we can't. Arsenal refits surface with that problem as the uppers and lowers are separated or one even replaced.
Another issues getting the nose of the upper to work with the barrel extension, when tightening the barrel nut to 30 ft lbs, it will likely be necessary to keep turning to get the sprocket teeth to clear the gas tube. Those teeth are there to keep the nut from backing off in use, which would be a bad thing in combat. Do get the tooth past the tube location, a maximum of 85 ft lbs is the top to keep from shearing the aluminum threads with the steel threads of the nut. It's not a complicated issue of a torque wrench or whatever, tho, much as some make out. If you can torque a lug nut you already know what is enough.
Same with some other assembly issues, fancy tools are not necessary, I used channel locks on the nut with the upper clamped in vice jaws - protective inserts were used.
Some absolutely cringe at marking up their firearm, tho, which is a mystery to be when it's a combat rifle to be used dragging it thru mud, bashed on the ground, etc. Drop and roll doesn't make a good environment for safe queens. Your mileage may vary.
As for quality, spending another $100 for a lower isn't all that. Most are forged by half a dozen makers, machined by another dozen shops, who put on the four or five dozen current roll marks. Forged lowers and uppers are a commodity item and paying three times more will not net three times more accuracy or reliability. What it will get you is a roll mark that might resell a bit higher, but used is used. Buy a roll mark you like or at least can tolerate - that seems to be the real criteria once you get past the hype and marketing. Be it known not even Colt drop forges, they machine platters - to control those little fitups on the assembly line.
Spend money on the barrel and bolt, shoot quality ammo, and it's going to be good to go. Pay special attention to matching specs of parts that work together, using the Crane Sopmod parts isn't overkill, and using a heavier buffer is less likely to cause problems than a lighter one. Be careful about the barrel length, gas port location, and size - it's both the "timing" and rpm limiter for the gun and control bolt speed. A slower bolt is preferred to a faster one to prevent bolt bounce and out of battery issues.
Here's the stickies at arfcom on assembly, not the absence of high end tools or their justification. I did eventually purchase the all purpose armorer's wrench for spanner use, you know how hard it is to find spanner wrenches in a hardware or tool store.
http://www.ar15.com/forums/t_3_4/22...__GAS_BLOCK___Step_by_step_instructions_.html
