Weapon construction is a modification that only applies to the rifle category of guns in Sniper Elite 5.
It is different from the cosmetic mod which can be unlocked for all weapons. But what does it do, and is there any point in bothering with it?
What does Construction do to weapons in Sniper Elite 5?
As you can probably at least guess, most guns are made of a combination of wood and metal. When it comes to a larger weapon such as a rifle, at least from this time period, the stock is generally made of wood. Now different kinds of wood have different properties as you know.
Some are tougher than others and some are much denser, therefore heavier.
Changing the construction on your rifle will affect how it handles. A Lightweight Elm construction will nake the weapon much lighter to carry, and the benefits of that are perhaps not as obvious as you might think - a lighter rifle increases your sprint speed for example, as you are not carrying as much weight.
Laminated Beech on the other hand has a more grippy texture which improves weapon handling.
Some rifles have different construction options than others. You can deck out the M1A Carbine for example in Heavy Walnut, which makes the gun slower to equip, but the added weight improves spread accuracy of your shot.
Once again, each individual modification you make to your weapon may not make a noticable difference on its own, but as the sum of all parts with everything else you do to it can make a dramatic difference to how it handles.