Would their be a big difference in accuracy at 100-200 meters if I were shooting with OPEN SIGHTS of these STOCK rifles:

-M14 (STOCK, no trigger job, no unitizing, NM FH, just stock)
-Stock PTR-91
-Stock FAL

JIM762

Your going to get a lot of different opinions on this.

As an HK fan and PTR owner ,I have to say,the
M1A is the most accurate stock ,open sights,
no mods and a relaxed firing speed.
Simply put ,the M1A has a huge advantage with a much
longer sight radius.
Usually ,a longer sight radius means slower repeat shots.

The PTR is second and the FAL last.
IMHO FAL stock sights suck.
Heated up with extremely fast shooting ,
PTR 1st ,M1A second ,and FAL far behind.
The FALs I've seen heat up and their groups spread
out quickly.
The fluted barrels on HK style rifles help them maintain
more of their accuracy at higher rates of fire.

Now ,a stock M1A with good parts is going to probably start at $1,200
and rise quickly.
A PTR starts at $700 and you can get about all you want (excluding pricy glass)
well before reaching that $1,200 price.

Just a thought .

how they shoot is up to you.

ammo is a big factor too Vasilli