Re: why do some sf snipers prefer 45acp?
The SF soldiers as far as I know are the only soldiers in the Army who have a choice. The rest get M9's as far as I know and there may be a few carrying glock unofficially because that is what we issue to Iraqi police and probably afghan police as well.
The 1911 has a better trigger than the M9 by a long shot, and that alone might have serious appeal. If the guns are well customized they can be very accurate, but I've seen some sloppy 1911's in need of serious repairs.
Loose sights, poorly fit barrels, magazines that are worn out and unreliable, finishes totally gone to the extent the guns rust without constant care- these issues stand in the way of the 1911 being really competitive in the Army circles where the guns are 50+ years old and may have seen 5-6 wars.
So really it depends on which group, who's armorer is worth a crap, and what work has been done, as the SF 1911 can be anything from a silk purse to a sows ear.
The marines are a whole different story- they've always taken their 1911's seriously, with custom Springfields, Caspian refit MEU pistols, and new Kimber pistols in supply. The Army is working with older pistols, less parts support, and less experienced armorers IMO.