Barrel length has little to do with accuracy, nor does barrel thickness.
I could design a 1" heavy barrel bolt gun that shoots worse than a hot mini-14 or a Romanian AK. Just give it terrible rifling, a nasty crown, or a sloppy big chamber. Then use ammo that has 200fps spread in velocity.
Accuracy has more to do with other factors, like the quality of the barrel. Quality handloads, quality barrel, a simple, tight, true action (like a bolt), bedding and free floating all come before having a fat barrel or longer barrel. Heavy barrel comes after those factors.
Heavy barrels are thought of as accurate because of being heavy, but in reality, their weight is one component of a "system" of features that increase accuracy. Almost all heavy barrels are also tight chambered, have quality cut rifling, and good crowns.
Thus said, any military pattern rifle aren't going to be super accurate. That's because feeding is more important than making a 1" group @ 100 yards. So the chambers are bigger due to being auto-loaders. Ammo isn't match grade. Velocity trumps accuracy for military use. Their action isn't the most ideal, they are designed to fire over and over quickly, not be accurate down to the tenth of an inch at 100 yards.
Target guns shoot MOA or less. Military pattern guns shoot MOM (minute of man) at the worst. If you get better, that is just icing on the cake. Most get better.
The SOCOM does what is was designed to do. IMO, it's too much money for what you get. Especially with Springfield being in bed with the Brazilians and their MIM processes.
A poor man's alternative to the SOCOM 16 would be a Saiga 308 16". AK actioned 308. Just as accurate, and leaves you about $1400 left over to spend $150 of which on a gunsmith to convert it to accept G3 mags. Looking at modern M1A's leaves me not impressed. I'd argue the commie rifle is more durable, more reliable and tough.