Eric Stecker
Well-Known Member
- Joined
- Jul 27, 2007
- Messages
- 292
I have noticed that the oal of my projectiles varies considerably. Is this normal with bergers or did I get a rough batch?
Lyons7STW,
It will be easier to address your situation with a bit more information. Which bullets do you have and what is the lot number? What OAL measurements are you finding in this lot? Have you shot these bullets to see how they perform?
It is normal for the bullet OAL to vary as much as .025. We work to minimize this result but OAL variation of this amount is not uncommon and within tolerances.
It is important to keep in mind that OAL is not as critical a dimension as others. For example, the variation on the distance from the base of the bullet to the end of the bearing surface (or where the bullet engages the rifling) will vary less than .003 and in many lots will vary only .001. Greater variation in this dimension can negatively impact performance.
The only way the bullet OAL variation will affect performance is if you also notice considerable differences in the OD of the meplat (tip). If the meplats are different diameters then the drag on these bullets will vary causing vertical dispersion.
NOTE: Some meplats will look as if they vary due to how the tip formed. It is important to mention that the critical dimension of the meplat is the distance from the outside edge to the other outside edge. Even if the inside of the hole looks different it won't matter if the diameter of the outside edge is the same.
The way we overcome this result even though we can't eliminate the bullet OAL variation of up to .025 is to slightly over point the bullets. This gets a bit complicated but I'll try to make this clear with an example.
If a bullet with an OAL of say 1.150 has an outside meplat diameter of .062 and another bullet with an OAL of say 1.125 has an outside meplat diameter of .080 then there is a problem.
However if the bullet that is 1.150 long is slightly over pointed then the excessive material is forward of the meplat but has no influence on the size of the meplat (it doesn't make it smaller or bigger) so it will not affect drag. This means that the drag or BC of this bullet is precisely the same as the drag of the bullet that has an OAL of 1.125 since the meplat's outside diameters are the same.
NOTE: Over pointing occurs when the bullet tip reaches the end of the ogive portion of the die. Some refer to the appearance of an over point as a "flare". At this point the material no longer makes a smaller meplat but rather makes a meplat of the same size by the material moving forward rather than inward. A meplat can only be as small as the hole in the die that allows the ejection pin to pass through the die to eject the bullet. So as long as the shortest bullet reaches this point on the die the bullets will perform just fine.
Eliminating OAL variation is extremely difficult and in many lots impossible. We set up each run to over point the longer bullets deliberately so that we significantly minimize or eliminate the affects of OAL variation on performance.
Regards,
Eric