Bullet speeds
Chronographs are nortorious for not being accurate......Most at best are only an estimate...And different barrels will shoot same loads at different speeds.Also a good chrono is exspensive.For true bullet speed you need to test a couple of units, and compare/average.....or,send loaded ammo away to a lab.(I believe White Labrotories still does this ) my Ohler 35P (500$unit)...will also vary...BUT not as much as the less exspensive units.
And most importantly............bullet speed is less important data than accuracy tests.
bill larson