If you read some of the old gunsmithing articles it would appear that the degree of action stiffness varied between manufacturers and action to action in the WWII production. This in turn affected the degree of compensation at various ranges. As when the Bisely finals were the decisive matches, the degree of long range compensation was important. That may have some affect on which action would be best for a particular distance given standard No4 service bedding and how true the front sight will be when zeroed.
Supposedly that was one of the Fulton Tricks that made their rifles desirable, though unfortunately when Major Fulton died some years ago all those records were destroyed. I have also read that part of the Fulton tricks were how they set up the bearings on the lugs to compensate for action twist due to asymmetrical support of the bolt, which in turn depended on the action stiffness.
The only difference I have noted in observation is that with Savage No4 MK I* rifles it seems a significant number need the front sight post to be zeroed to the left of center, which might have something to do with the metal heat/treatment. That is with standard service bedding.
In the
Canadian
case, they allowed only the standard front loaded bedding from 1946 until the adoption of the No 4 in 7.62 around 1963. Only one exception was made for an English team that came over around 1955/56 that had some center-bedded rifles that were allowed. The Canadian had pretty good luck with Longbranch rifles, their scores at Connaught seem to be very good, though I note that most of the winning Bisley Canadian shooters pre 1962 seem to have a match tuned No1 MK III for the Bisley finals when they came over as a team to the
UK
.
Not a real answer, but it might explain why some folks though the WWII actions were better for target work in some way.
It might also relate to the barrels and bore size, as I recall talking to an old time shooter at Connaught two decades ago about this and he said back in the day a lot of the issues folks had with accuracy had to do with the fouling characteristics of different lots and the relationship to bore size. I do not really recall the details well enough to say anything definitive, but I seem to recall him saying the post war BSA barrels were very fine barrels.