Barrel length, in and of itself, has little to no effect on accuracy. Barrel quality does. Barrel length effects velocity. More barrel, more room to accelerate = more velocity.
Heavier barrels have a tendency to move around less during firing, and to change point of impact less when they heat up, than lighter barrels, so, all else being equal, a heavy barrel is considered more accurate. If you're firing occasional shots, i.e. the barrel cools down between shots, the issue of heat response is moot. My kid's lightweight Ruger M77 sporter shoots sub MOA when slow-fired.
A recessed crown is protected from inadvertent dings, and therefore protects the crown from deformation should you be so careless as to bump the muzzle against a hard surface. A target crown is produced with special care and provides an extremely square and true release point for the bullet, therefore allowing the bullet to fly straighter from shot to shot, or so is the current wisdom.
The only HUGE differences will be from a damaged crown, a damaged or worn-out barrel, poor ammo or, most importantly, the difference from one marksman to another. Almost all firearms shoot better than their owners.
HUGE is of course a matter of opinion. Some people would consider a 1/2 MOA difference to be HUGE, while others would never notice.
Update: I'll ad that a flash supressor makes for a superior "recessed crown" in that the entire muzzle end of the barrel is protected. I refer to a flash supressor (or a brake) as a "muzzle protector" first and foremost.
Update#2: Since you mention military barrels; our military has specifications that must be met before a shipment of rifles is accepted. I don't know what they are today, but during military production of the M-14 the "rack grade" rifles had to be capable of placing 5 rounds withing an area a little over 6 inches in diameter at 100 yards using standard military ammo. This would be considered dismal accuracy by today's standards, but it was good enough to take a communist out of a fight. Understand that many of these same rifles would be capable of much better accuracy-- this was simply the minimum performance standard. And since you mention barrel weight; the military "Match" grade M-14 had all the same dimentions as the standard, rack-grade M-14 (same barrel weight and profile). The difference was that the tolerances (the acceptable dimensional variations) were cut in half. It was simply made to higher standards.
The bottom line is that it is not the particular features that matter so much in the end, but rather it is the quality. Sometimes even then it takes a deal of experimentation to find the right combination of rifle and ammo, and shooter, to get the best performance.