Density of the wood can vary greatly in the woods. I have seen such a difference to over a pound on duplicated rifles, but one soft maple & one very hard dense maple.
However, if you tell us what you are wanting to build & the barrel length, caliber & Class of barrel (A,B,C,D wgt) of swamped or size across the flats on a straight barrel, type of wood, some of us may have built one similar & know a weight close. :m2c: