This is a thread which has asked more quaestions than have been answered. The intial question was something along the lines of, "Why spend a whole bunch of money for a 308 which shoots about the same as the one I have?" Well, if performance on the target is your primary criteria, there may well be no reason to spend more. The truth is, there is indeed a limit to what you can do with a 308 regardless of the amount of money you throw at it. Having said that, I will confess to being impressed by the accuracy shown by some of the better tactical customs. They are still 1/2 minute rifles but they are very consistent half minute rifles. Still, a less expensive rifle which shoots as well, shoots as well and that's all there is to it. The shooter just has to be content with being able to brag about the targets he produces rather than the amount of money he spends.
I may have had one 308 which was a near-quarter minute rifle. This was a 10 1/2 pound 308 with which I once fired an aggregate of around .27. I recall the fifth group had one shot out which opened that group up to over 1/2 inch (fatigue). Plainly, the other groups were small. The best group was a .128 and there were two others under 1/4 inch. That was the best agg I ever fired with a 308 and I never came close again. At the time time, I was shooting a lot of BR and was doing fairly well at it. Anyway, that was a good 308. I have had a bunch which were honest sub-half minute rifles and my current 300 meter "F" class rifle may be a 1/4 minute rifle but it's not what I would call a "practical" rifle. The practical 308s are probably shooting at the 1/2 minute level when I have to contend with witnesses. Considerably better than that when I'm alone!
Barring insufficient twist or an ammunition deficiency, a rifle which shoots well at close range will shoot well at long. The action will have little effect.
The exception to this is, of course, the #4 which was well known for it's ability to compensate for velocity variations. A good Lee Enfield might shoot quite poorly at 300 but would really shine at 800.
I think it is fairly easy to produce a real 3/8 minute 308 but it is very difficult to truly shoot it to that level.
By the way, are motorcycles in Europe not governed? I can recall German riders complaining about being limited to 100 horsepower and having to come over here to ride the real stuff. Really a moot point in my case. At this stage in my life, slowing reflexes and shriveled testicles govern my speed! Regards, Bill