Re: Accuracy Int'l AE 308 questions.
I believe to better advise you a couple of things I would consider:
1. primary application: if you are going to the range, benching or competitive shooting, I would recommend the 24" barrel over the 20" any day of the week. If you are planning on tactical training, 600m range shooting and less or require compact system, the 20" would be my choice. There are many reasons to go with either one up front, but remember, you can always purchase the other later for installation to afford you the other opportunities as well, so not a real issue.
2. Suppressor usage, 20" more desirable for obvious reasons on overall length.
As for the muzzle brake, that is a personal choice there. The AI standard muzzle brake is ok, not my favorite for sound, signature and reduction. The AI magnum brake is much better in all aspects in comparison to the standard, but is more expensive. The new SAS QD brake we offer on the Bartlein barrels is truthfully my favorite for all around usage as a muzzle brake in comparison. The AI brakes are installed with a M18x1.5 and can be easily removed and reinstalled. The SAS QD is a timed and not recommended to be removed for suppressor installation. Hope this helps.