Not M39, but Lee Enfield - WWII instructions to armourers is available - I think they wanted 0.030" clearance around the barrel (so from main stock AND from hand guard) except where front of receiver is solid to main stock and several pounds "up pressure" at forearm tip. I believe target shooters improved on the basic military bedding, AFTER the War. I think with "mid-bedding" and "packing", the complete "free floating" of the barrel went away. One of my more accurate 243 Win was epoxy bedded solidly from rear receiver tang to front of forearm (a Remington 788). Many very accurate rifles have "smoked and scraped" fitment of stock to barrel - so "free floating" is only one way to get a very accurate set-up - but "free float" is probably the quickest and the least manual labour involved. But that "solidly bedded" also relies on the stock wood not taking on or giving off water - shooter does not want that stock to warp - "bedding went sour" - from the days when GrandPa cut down the tree; Dad dried it, GrandSon carved it into a stock - so "decades" of prep for a rifle stock