My friend has a Win. Model 70 in .308. He used some surplus I gave him and said One round was louder and kicked more which he attribute to a small hair-line crack in the fore-end. Without causeing any other damage to bolt or barrel and wth no blown case, how could he be right? Isn't it more likely the gun was bedded wrong or there was improper contact and recoil and vibration found a weakness already in the wood. Any thoughts, Please!

Was the "surplus" US military surplus, foreign military surplus, handload?

Was the inside of the stock and the area of the recoil shoulder examined for signs of the crack all the way through?

Was headspace checked to ensure no bolt setback?

The crack could have been caused by an overly hot load, poor bedding, or, more likely, a combination of the two. Could have been there, unnoticed, already. Not something that can be determined without examining the rifle.

But, the important thing, for your friend's safety, is to make sure the gun is safe to fire.
A check by a good gunsmith is in order.