Looking at images at various resellers, it appears that the buffer and spring are shorter.  Will it work on a non-carbine rifle?  I guess part of the confusion is what constitutes a carbine?  Is it the 16 inch barrel and carbine length gas tube?  If I have an 18 inch barrel and a mid-length gas tube, will a carbine stock work?  Some explanation to further my understanding would sure be great.

Thanks.

Think of the upper group and the lower group as two separate things.

You can have a rifle length gas system  and 18 or 20 inch barrel upper and put it on a lower with a carbine stock.
Or you can have a carbine length gas system wit a 16 or  14.5 or 10 inch barrel upper on a lower with a rifle stock.

In general, the standard configurations are:
a rifle gas 20 inch barrel on a lower with a rifle stock.
Or
A carbine gas 14.5 inch barrel on a lower with a carbine stock.


The stocks have completely different receiver extensions, springs and buffers among other parts.  
And the carbine stocks/ sized buffers have different weights for different configurations.

Do a bit of searching and reading and it will become clear quickly.

carbine stock would be the adjustable ones (shorter receiver extension than the A1/A2 fixed rifle stocks), they have a shorter, stiffer spring, and a shorter buffer. The standard weight buffer is a bit lighter than the rifle buffers as well.

ETA: too slow