warf73, There are several rifles that use a tapered throat. This acts much like a forcing cone in a revolver. Yes, some Weatherbys and all Sakos and Tikkas have this. Many European military guns such as Mausers also have a tapered throat. In these guns, long bullets are used so it's more important to get the bullet started straight in the bore than what happens when the base is flush with the case mouth. Most guns with tapered throats are very accurate and not fussy. Sako and Tikka guarantee 1 MOA right out of the box. The down side to a tapered throat is barrel life. Assuming the same ammo and the same metal in the barrel, a tapered throat will erode much faster than a conventional throat. Throat erosion will distort the bullet and result in poor accuracy. Sako and Weatherby use some mighty fine metal in their barrels so erosion is minimized. As for your rude comment, you are looking at a sample rate of one vs the hundreds I have tested. You also happened to note one of the rifles that are an exception to normal.
As for most US made barrels, the bulk of them use a 2 degree taper, compared to an 11 -18 degree taper in Sakos. The almost square 2 degree taper is not really enough to matter. Some of the new Savage rifles now use a tapered throat too. I suspect we will see other US made guns going to the taper concept some day.
Tycer, Bullet upset is usually caused by exceeding the velocity for the twist rate, badly fouled barrel, or a bad crown. I could see a bullet keyholeing well down range because of short brass and bullet distortion.
beemanbeme, In your example, the bullet would be well started into the bore but there is about 50,000 psi on the bullet base that will do some weird stuff. Think of a 25 ton punch press pushing a relatively soft bullet into a hard undersized hole. It will deform it if the bullet is the slightest bit off center with the bore. This is why many bench rest shooter turn the necks on their brass. When extreme pressure is applied from firing, the soft brass case will puff up to the chamber dimensions. Should the brass be a tad thicker or thinner in one area, the bullet will not see a perfect round hole and can get started into the bore a fraction of a degree off center. Now the extreme pressure pushes on the bullet base and distorts the shape of the bullet slightly. The bore will iron out some of the distortion but will leave the bullet slightly out of balance with the axis. Once the bullet gets in flight, the off axis distortion will cause the bullet to act almost like a whiffle ball. At ranges of 200 yards or less, you probably won't see much difference except the groups won't be as tight. Further down range, the bullet's spin will decay enough where it will start to yaw and eventually tumble.
When long bullets are used, most of the bullet is well into the bore by the time the base flushes with the case mouth. This may still cause some bullet distortion but not nearly as bad as a .224" short bullet would see.
If you measure the diameter of a spent case neck, you can easily see how some unoccupied free bore (from short brass) would have enough room to allow the extreme pressure to push the bullet off center. Typically, the free bore is about .025" larger than bullet diameter. This assumes a .012 neck thickness and an extra thousandth to ease chambering. That's a lot of free space, more than 10% of the bullet diameter in your example.
Free flight? Don't think so. Just an unoccupied gap that can allow a bullet to get a wee bit off center. "Are you saying during the nanosecond in which the base of the bullet is neither in the neck nor in the rifling will distort the base of the bullet and degrade accuracy??" Yes, that's exactly what happens. The reason the concept is hard to grasp is the pressure element. Put a bullet on an anvil then take a small hammer and give it a light whack. No doubt, the few psi you influenced on the bullet made it distort. Now think about what 50,000 psi would do.
No matter what caliber you shoot, keeping the brass neck as long as possible will minimize bullet distortion, abet less so when long bullets are used. The real key is to get the bullet started straight into the bore, no matter what diameter or length of bullet you use. There are a lot of things we can't see or measure but have an influence none the less. Example: the neck of a brass case is seldom uniform in hardness or thickness. When a round is fired the brass doesn't puff up perfectly uniform. In that fraction of a second when the bullet is released, the non-uniform hardness or thickness can cause the bullet to be released a tiny bit off center. This causes bullet distortion when the ogive hits the bore. There is a simple solution for this. Annealing the brass from shoulder to mouth will virtually eliminate the problem. You really don't have to turn the necks either. The brass is so soft that it puffs and releases the bullet quickly and will iron out imperfections in thickness.
If you want to do just a few simple things, you can make a "problem child" gun into a good shooter. Keep the brass as long as possible and a uniform length, anneal the cases, seat the bullet to the right depth, use quality bullets, and weigh each powder charge.
