You have heard the old saying, "The weakest link in the chain". Well, 400 and 500 yard shots are nothing to take casually. If you are set up with the right gear and an accurate rifle you know well, these are relatively easy shots.
But, not all rifles are 400-500 yard rifles by any stretch of the imagination.
Other things to consider is the consistancy of the rifle. Talk with any other rifle maker on this board or anyone that has gotten a rifle from one of the top smiths on this board and most will say how consistant their rifles are from load to load and that the endless search for that mystical load that shoots great is not all that difficult to find and that in fact, most loads shoot extremely well in their custom rifles
The reason is because the rifles are sound in their foundation, receivers are true and square, bolt lugs have full and square contact to the receiver, Recoil lugs are surface ground and true on both sides. Receiver threads are recut on perfect axial alignment with the axis of the receiver, Barrel threads are on the same axis and true and cut to a very high quality thread fit to the receiver, barrel shoulders are square, chambers are cut properly so they are perfectly aligned to the bore and crowns are cut perfectly concentric to the bore as well.
Stock bedding is even and stress free and generally the receiver is riding on an aluminum block or on metal pillars and barrels are free of any contact from the stock.
All this adds up to most custom rifles shooting most loads extremely well.
In many cases with a factory rifle or a rifle that is not properly built, you get that finick personality with the rifle. You can also see the occasional fliers that you have no explination for. Generally, these issues are due to machining flaws in the rifle system. Small ones add up and result in these issues.
Simply put, if you want the rifle to perform up to its ability the very first step you should do is accurize the receiver.
Remember though, there are different ideas on what is a properly accurized receiver. In my opinion, unless the receiver is machined using the tooling from Greg Tannel and using his techniques or those similiar to his using the same basic ideas, a receiver will not be properly trued.
Just my opinion,