Excellent rifles. Probably accurate as any off the shelf AR308. But everything is proprietary. No other uppers will fit their lower and vice/versa.
Magazines are FN-FAL metric type magazine design. They sell polymer mags made by Thermold that work really well, but you ain't gonna stick a Magpul in it and make it work. The entire design was bought from Bushmaster (the old, good Bushmaster company-2nd gen) and they designed it around FN-FAL magazines. I think they grew on trees in the Congo back then. I have one of the Bushmasters.
Barrel nut and handguards are proprietary. Don't know for sure about barrels.
I'm not trying to get you to buy something else --- I think they are good quality guns --- but you need to understand from the get-go that you'll have to buy any upgrades etc from RRA.
Most small internal parts will interchange, like triggers etc. But Bolt carrier groups, buffers, buffer tubes, will not interchange with anybody elses stuff. Heavy Buffers makes a special buffer/spring combo for it which I highly recommend.
If this doesn't bother you, go for it. You'll be buying a good quality weapon from a good company. If you need a little better compatibility with commonly available parts/mags then look elsewhere.
All the above only applies to the LAR8. Their AR15s are interchangeable with any other AR15.
