Hey all. I was reading on here that 168gr bullets are not good for longer distances than 800m. Some one commented that they aren't good for the long range for the same reason they are good for 100m.
Can anyone explain to me how come? If this truly is the case.
Thanks.
While I can't explain other people's comments, one of the key issues regarding bullets and their suitability for long-range shooting is their ballistic coefficient (BC) relative to other choices. All other factors being equal (muzzle velocity, acceptable barrel twist rate, bullet shape, etc.), longer, heavier, pointier bullets will have higher higher BCs than others. BC is a measure of drag that a bullet experiences i.e. how much it is slowed by friction with the air and is pushed by cross-winds. This translates into less drop and windage for higher BC bullets. Also, some bullets will become unstable as they become slower than the speed-of-sound and undergo erratic changes in flight-path resulting in unpredictable POI.
In a 308, 168 grain bullets have a modest BC as compared to heavier 308 bullets such as the 190 Sierra Match King (168gr Amax (.475 BC) vs. 190gr SMKs (.533 BC)). So bullets with a higher BC than a 168 tend to be better at longer ranges.
For a 100m bullet one might consider flat-base bullets which can be more "accurate" (i.e. exhibit more precision) than the lower BC boat-tail bullets. Flat base bullets are still a favourite of many bench-rest shooters. The reason is that flat-bases tend to be easier to manufacture and thus are more likely to be consistent than boat-tail bullets. Also, the boat-tail is more affected by lack of concentricity in the bullet-base and/or in the barrel due to the flow of muzzle gases past and around the bullet when it exits the muzzle.
At longer ranges, the lower BC of boat tails overshadows the benefits of flat base bullets.
See below a quotation attributed to Gale McMillan of McMillan barrels:
“If you consider the way a boat tail bullet is made you will understand that it is an impossibility for the tail of the bullet to be inline with the body. If the tail is formed in the upper punch it will always be off by half the amount of the clearance between the punch and die. If it is made in the lower punch it will be a wider tolerance since there is more clearance in the lower punch. With the tail of the bullet being off center by at least 1/2 a ten thousandth of an inch, this keeps the bullet from flying true.”
“That is the reason you don't see them used in competition (Bench Rest, that is). We will hear a loud cry from long range shooters and all I can say is the ability to lay on ones belly and shoot 1/10 moa is an impossibility so they can get away with using them since the error factor is still smaller than the shooters ability. There was a remark made above about a flat base shooting better in a factory barrel and I will change that and say any barrel! My favorite saying is the records speak for its self. Show me a national benchrest record shot with a boat tail bullet. One thing that clouds the issue is that no high power match bullets are made with a flat base so they can only be compared with custom match bullets made with flat bases of which there are few.”
“I will say that the small amount of loss of accuracy is off set by the ability to overcome conditions due to decreased flight time at ranges of 600 and beyond.”
