I'm planning on picking up an AR time in the near to very near future and am coming for some help. Here is what basically I have planned for the rifle: a plinker will be its #1 chore and most realistic, SHTF would be a second. I have no prejudice towards any manufacturer but kinda like the looks of Cavalry's polymer lower. So on with the questions. Most of these have been beat to death but the search feature and me sometimes go round and round.
1: What is the preformance difference between the 16" barrel and the 20". Velocity loss? Less expansion?
2: How do the different uppers work? I have a Cetme in 308 and would love a FAL or M1A but if I could just slap a 308 upper on my lower that would be great. I know the Cavalry lowers take GG mags for .45. Do they take a FAL/G3/M1A mag for 308? What other lowers can take pistol and 308 mags?
3. This one is very subjective. What would your ultimate rifle be? I'm looking at this as possibly be the last EBR I can get and want to make it as good as I can.
Thanks for bearing with me.
To answer number 2, no you can't put a .308 upper on an AR15. Only calibers with an overal length the same as or shorter than the 5.56 can be used. The magazine would never fit in the mag well. The ARs that you see in .308 are AR10s and are larger than AR15s.
Edited to add:
With the exception of single shot uppers like .50bmg that just use the lower as a trigger group.