I am wanting a rifle that will be well suited for 400-750 yards. So, if you tell us what you intend to do with your build, we can lay out the pros and cons of each choice and help you select the proper pros and minimize the cons. In other words, there is no need to spin a bullet faster than it needs unless you have no choice. It will of course, stabilize any bullet shorter than my selected ones, but a slower twist would have sufficed for that and I am a big proponent of using the slowest twist needed to statically stabilize the bullet you want to shoot. 308 rifle for one single purpose F-TR at Long Range (800/900/1000yards.) The rifle is NOT suited for anything else (well, it will do fine at shorter ranges, but it is almost overkill.) It has a very long heavy barrel and its twist was selected to properly stabilize a narrow range of bullets, I am not talking this rifle hunting. When you have decided what the answer is to that question, you build the rifle so that it will be at its best for most of its use. It comes down to one simple question: What do you want to do with your rifle? Srv656s and koolnhard, thank you for the kind words.Ġ3psd, yes it is an interesting subject and it is easy to let it get complicated but let me boil it down for you. Finally, launching a 200gr bullet with a high BC, will require a minimum MV so that the recoil might be more than you want to deal with. In other words, substance is somewhat more important than style, but you still need style.Īnd for the long distance, you still need a certain muzzle velocity to have the BC work for you. This tells you that streamlining or increased SD can take you further by increasing the BC, but a combination of streamlining and especially an increased SD will do a better job over the longer distance. The 175SMK has a BC about the same at the top end as the 155 Palma, but as the velocity reduces, it has a higher BC value, because its sectional density is higher that the 155gr Palma. 221, which is pretty good but its shape was not very aerodynamic. Remember what I said earlier, the BC is a function of the SD and the shape. 308 front, the 155gr bullet is making use of its very aerodynamic shape to increase its BC value. This is such a big increase that even though my 80gr start out almost 400FPS slower than the 55gr bullets, by the time they get to 500 yards, my 80gr bullet has overtaken the 55gr bullet, which is now falling on the ground as it goes subsonic, my bullet will stay supersonic past 1000 yards. If you use an 80 grain bullet, the SD for that bullet will jump from. So we make the bullets longer.īack to our. The point is that we are currently stuck with jacketed lead, unless you have access to materials that mere mortals do not. Consult you nearest periodic table and alloy manufacturer. Depleted uranium works well for that, as does gold, platinum, carbide, tungsten, etc. In order to increase the sectional density of a bullet, you can make it heavier (and if it's in the same caliber, it will be longer) or you can use materials than have a higher specific gravity (density) than jacketed lead.

Sectional density is a function of the weight of the bullet in a specific caliber. The ballistic coeeficient is a function of sectional density and shape of the bullet. So, you try to increase the ballistic coefficient of the bullet such that it will retain more of its initial velocity longer. you can try to push a bullet as fast as you can, but if the bullet has a low BC, it simply sheds this extra velocity faster. When people started wanting to shoot longer distances, the low ballistic coefficient of these original bullets was working against them. 308 Winchester was originally loaded with a 147gr bullet (I forget the length) and it did well for its intended use, up to mid-range (600 yards and under). These bullets are fine for the original intent which was short range, 300 yards and under. Some years later, the bullet weight grew to 62 grains but since it had a steel penetrator, the bullet was longer because of the lower density of the steel. 75 inch 55 grain bullet with originaly a 1:14 twist then a 1:12 twist. Let's take 2 calibers that are well represented here.

Definition of subsonic bullet