It's the way the stock fit on bolts compared to minis, on the mini they are secured by the trigger group and pulled against the stock. The bolt gun is usually fitted by 3 screws and floated off the action with not much to secure the forearm of the stock. The gas block also helps secure the mini stock from movement. Wood is best for bolts because it's ridged. The mating areas of the mini help the stock to be ridged.