Does barrel lenght play a role in your buffer selection?
I am swapping out my standard solid rifle A2 stock for a Magpul ACS on my Bushmaster AR w/ a 20 inch barrel. I understand I need to replace the whole buffer system. Does the size/weight of the actual buffer (part that goes inside the spring, just to be sure I'm not confusing terms) matter based on the size of the barrel?
you'll need a carbine buffer.
never put a rifle buffer in a carbine receiver extension.
there're different carbine buffers available: Standard (~3.0oz), H (3.80oz), H2 (4.60oz), H3 (5.40z), etc.
you should use the heaviest buffer that will still keep your AR reliable.
What he said.
Like the Sig Frens.
Standard should be fine, H would be okay too.