I am considering a FAL carbine build and am wondering if it is truly practical to have a rifle in .308 with only a 17 inch barrel. My liking of this caliber stems from the fact that it is powerful and performs at distance. At the moment I have a 21 inch version as it fulfills this role perfectly.

What kind of performance loss in terms of point of impact, velocity, and fragmentation (if that even happens at 21 inches) occurs with a 17 inch barrel versus a standard 21? Also, would an M4 be better suited for a carbine role in any case?

You will lose some velocity, but you will still have a long range. I know that many, many people have short barreled .308s and they seem to work fine. For a defensive weapon the M4 would be much better, especially if your collection already has an FAL.

Quoted: I am considering a FAL carbine build and am wondering if it is truly practical to have a rifle in .308 with only a 17 inch barrel. My liking of this caliber stems from the fact that it is powerful and performs at distance. At the moment I have a 21 inch version as it fulfills this role perfectly. What kind of performance loss in terms of point of impact, velocity, and fragmentation (if that even happens at 21 inches) occurs with a 17 inch barrel versus a standard 21? Also, would an M4 be better suited for a carbine role in any case?

I chrono'd my BH 168 gn .308 at 2550 fps at 10  ft from my 16" AR10.  The BH factory specs say 2650 fps which I presume is from a 24" barrel.  So not much velocity loss IMO.

DRD

.308 gets almost all of its velocity, at least with 168gr loadings, in the first 20 inches of barrel.

Quoted: I am considering a FAL carbine build and am wondering if it is truly practical to have a rifle in .308 with only a 17 inch barrel. My liking of this caliber stems from the fact that it is powerful and performs at distance. At the moment I have a 21 inch version as it fulfills this role perfectly. What kind of performance loss in terms of point of impact, velocity, and fragmentation (if that even happens at 21 inches) occurs with a 17 inch barrel versus a standard 21? Also, would an M4 be better suited for a carbine role in any case?

Probably 99.9% of all the G3s ever made had 17.75" (450mm) barrels.

Never heard any complaints about their performance.