A book on rebarreling Mauser actions had sectioned original barrels that showed amazingly long freebore sections. This doesn't seem to have made such bores inaccurate , but I suppose it could have an effect noticable where maximum accuracy of benchrest competition is concerned.
Long ago I had considered buying one of the first of the Remington 600 rifles to come out in .308. Of course I often wish that I had nowdays whether I'd ever shot it or not, but the store owner went into fits when I mentioned using 7.62 NATO surplus ammo. He told me that there had been 600 models damaged by using 7.62 NATO due to much of the military ammo using bullets that were designed for the long throats of military chambers, and that he would have to ask for a signed statement from any buyer that only commercial .308 ammo would be used to avoid possible liabilty suits. The owner apparently had been hounded by lawyers before over other matters and I'd noticed he was very leery about selling any milsurp rifles, though his father when living had built the business on milsurp rifles and had one of the largest collections of rare WW2 and WW1 rifles in the US prominently displayed on the upper walls of the shop.
I heard much the same when I bought my Remington 788 rifle, I'd been looking for a .308 but the only store carrying the 788 chose to handle only the .243 and smaller calibers, the salesman there also said they'd received warnings against using Military 7.62 ammo in Remington Chambers due to a difference in the throat.
The More modern .308 Remingtons, especially those with the 5R rifling may have become standardized on a throat size that will accept all the military bullets. The Remington being the standard US Miltary 7.62 Sniper Rifle these days and probably their bread and butter gun.
I had recently been examining some post WW2 manufacture Belgian FN Manufacture Machinegun ammo in .303.
The bullets of these differ greatly from any of the British bullets I've seen, and besides its unusual boat tail taper the front portion of the bullet has a much fatter appearance, the curvature of the Ogive being more rounded.
This ammo was intended for maximum range and accuracy from a machinegun bore and I have my doubts about using it in even the generous throat of my Enfield barrels.
I suspect that reported problems of 7.62 NATO surplus in .308 rifles may in large part be due to some of the military long range ammo being given a bullet shape intended to minimize the effect of Freebore and oversized or eroded throats of machinegun barrels.
The Remington Military Sniper rifles are optimized for the M118 Long Range Special Ball, which is a fairly high intensity load using a 175 grain bullet, so its throat may be on the long side for the much more common 150-155 grain loads. Then theres the extra heavy bullet long range and heavy game loads to consider, bullets of up to 220 grains often with chamber pressures very near the SAAMI maximum safe limits.
A touch more room at the throat is likely intended as a safety factor, in part because sporting ammunition manufactured in Europe may have bullet profiles better suited for the Mauser style freebore.
I did find that seating 150 grain Hornady bullets further out than the crimping groove indicated greatly improved accuracy when used in my WW2 era Savage No.4 rifle, the original bullet type having been a very long 174 grain bullet closer in size to a 200+ grain bullet due to the lightweight nose insert of the MkVII bullet, and the throats of rifles optimized for the MkVII bullet while having a tighter throat than those optimized for the earlier 220 grain Round Nosed MkVI bullet probably mintained enough clearance to allow safe use of MkVI ammunition when necessary since both were often in use at the same time in far flung outposts and shortages could require substitutions in an emergency.
