Re: FREEBORE ON WEATHERBYS
Hello Light em up
There are two surfaces in the bore that contribute to the length of freebore.
The first being the freebore area, and the second being the throat. The throat area is a variable because of different Ogive’s. Depending on the ogive radius and throat angle this will determine where the bullet will actually touch the lands and must be added to the overall length of the freebore also.
Usually the length of the freebore is somewhere in the neighborhood of .5 through to 2 times the diameter of caliber (most factory rifles), however Weatherby rifles are much more than that somewhere around maybe 3 to 5 times the caliber diameter.
Some say the radius venturi design of his cartridges are one of the reason they have such a long freebore length, and the other being a much more influential reason for freebore, throat erosion. His cases and his loads found in a about every manual are higher than other comparable cartridges. The pressure spike is a lot different when you have a lot of freebore and are not placing the bullets near the lands. You will see an increase of velocity because of this, the bullet hasn’t hit the lands and the pressure spike hasn’t jumped much until your bullet contacts the lands.
Usually the freebore diameter is between .0005 (benchrest) and .002 (factory) bigger than the actual bullet. When using jacketed bullets the pressure behind the bullet will actually deform it a small amount and seal this gap. You wont lose any measurable difference of velocity where this gap is concerned. It happens in milliseconds and the length of the freebore, well you do the math and see if you can come up with any number that doesn’t have 13 decimal places after the decimal.
Accuracy of rifles with long freebore lengths generally is not as good as ones with little or no freebore. Like most of the manuals say, (Weatherby rifles) “load the bullet so that it fits into your magazine this should net you the best accuracy” minus about .035 thou to keep your noses from being smashed.
One way around all of this if your looking for paper punching is using VLD style bullets and loading them so that only the boatail of the bullet protrudes into the case past the shoulder intersection.
This will also allow you to utilize a greater case capacity. Longer bullets will get you close to the lands and possibly even touch the lands if you’re lucky.
Well good luck with your rifle and shooting.