>>64158823
Anon is correct. Building M14s is pretty straightforward on paper but the devil is very much in the details. Things have to align correctly and tolerance stacking is an absolute bitch, this is true of any Grand derived design because the whole system is somewhat like stepping stone between bolt actions being converted to self loaders and modern automatic rifles. It does work, and it can work very well indeed, but an absolutely inordinate degree of care must be taken to do it right and to do so consistently across serial production is a nightmare task. This is very unlike an AR-15 where tolerance stacking can happen, but the design is fundamentally better to where you can get away with lots of small mistakes without messing up the final product too much.
For instance if you have upper/lower play on an AR you can just shim it. Even if you don't fix it all the accuracy is determined by the upper so most shooters won't notice, and there's enough leeway with hammer drop/magazine alignment/buffer tube to upper fitment that it'll work fine.
If the stock on an M14 is loose you absolutely have to fix it or you'll get shotgun patterning. Changing out a trigger group can affect fitment and therefore accuracy. Things on an AR are more compartmentalized and modular.
>>64158891
They didn't do it perfectly. They were notorious for soft bolts, horrible fitment, crappy barrels and awful chu wood stocks that are worthless on an M14. The two redeeming features are the price point and hammer forged steel receivers. Even then, some of their forged receivers were done wrong and ended up too brittle.
M14 builders typically buy polytech rifles and strip them down to the receiver, using either custom or USGI parts for everything else.
